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<h1 class="type-name">
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<span class="kind">module</span> DB::QueryMethods(Stmt)
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</h1>
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<h2>
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Overview
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</h2>
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<p>Methods to allow querying a database.
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All methods accepts a <code>query : String</code> and a set arguments.</p>
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<p>Three kind of statements can be performed:</p>
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<ol><li><code><a href="../DB/QueryMethods.html#exec(query,*args_,args:Array?=nil)-instance-method">#exec</a></code> waits no record response from the database. An <code><a href="../DB/ExecResult.html">ExecResult</a></code> is returned.</li><li><code><a href="../DB/QueryMethods.html#scalar(query,*args_,args:Array?=nil)-instance-method">#scalar</a></code> reads a single value of the response. A union of possible values is returned.</li><li><code><a href="../DB/QueryMethods.html#query(query,*args_,args:Array?=nil)-instance-method">#query</a></code> returns a <code><a href="../DB/ResultSet.html">ResultSet</a></code> that allows iteration over the rows in the response and column information.</li></ol>
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<p>Arguments can be passed by position or as an array.</p>
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<pre><code class="language-crystal">db.query(<span class="s">"SELECT name FROM ... WHERE age > ?"</span>, age)
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db.query(<span class="s">"SELECT name FROM ... WHERE age > ?"</span>, args: [age])</code></pre>
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<p>Convention of mapping how arguments are mapped to the query depends on each driver.</p>
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<p>Including <code><a href="../DB/QueryMethods.html">QueryMethods</a></code> requires a <code>build(query) : <a href="../DB/Statement.html">Statement</a></code> method that is not expected
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to be called directly.</p>
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<h2>
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<a id="direct-including-types" class="anchor" href="#direct-including-types">
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<svg class="octicon-link" aria-hidden="true">
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<use href="#octicon-link"/>
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</a>
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Direct including types
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</h2>
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<ul class="other-types-list">
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<li class="other-type"><a href="../DB/SessionMethods.html">DB::SessionMethods(Session, Stmt)</a></li>
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<li class="other-type"><a href="../DB/SessionMethods/PreparedQuery.html">DB::SessionMethods::PreparedQuery(Session, Stmt)</a></li>
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<li class="other-type"><a href="../DB/SessionMethods/UnpreparedQuery.html">DB::SessionMethods::UnpreparedQuery(Session, Stmt)</a></li>
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</ul>
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<h2>
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<a id="defined-in" class="anchor" href="#defined-in">
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<use href="#octicon-link"/>
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</a>
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Defined in:
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</h2>
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<a href="https://github.com/crystal-lang/crystal-db/blob/v0.10.1/src/db/query_methods.cr#L21" target="_blank">
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db/query_methods.cr
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</a>
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<br/>
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<h2>
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<a id="instance-method-summary" class="anchor" href="#instance-method-summary">
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<use href="#octicon-link"/>
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</svg>
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</a>
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Instance Method Summary
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</h2>
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<ul class="list-summary">
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<li class="entry-summary">
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<a href="#exec(query,*args_,args:Array?=nil)-instance-method" class="signature"><strong>#exec</strong>(query, *args_, args : Array? = <span class="n">nil</span>)</a>
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<div class="summary"><p>Performs the <code><a href="../DB/QueryMethods.html#query(query,*args_,args:Array?=nil)-instance-method">#query</a></code> and returns an <code><a href="../DB/ExecResult.html">ExecResult</a></code></p></div>
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</li>
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<li class="entry-summary">
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<a href="#query(query,*args_,args:Array?=nil)-instance-method" class="signature"><strong>#query</strong>(query, *args_, args : Array? = <span class="n">nil</span>)</a>
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<div class="summary"><p>Executes a <em>query</em> and returns a <code><a href="../DB/ResultSet.html">ResultSet</a></code> with the results.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query(query,*args_,args:Array?=nil,&)-instance-method" class="signature"><strong>#query</strong>(query, *args_, args : Array? = <span class="n">nil</span>, &)</a>
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<div class="summary"><p>Executes a <em>query</em> and yields a <code><a href="../DB/ResultSet.html">ResultSet</a></code> with the results.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_all(query,*args_,args:Array?=nil,astype:Class)-instance-method" class="signature"><strong>#query_all</strong>(query, *args_, args : Array? = <span class="n">nil</span>, as type : Class)</a>
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<div class="summary"><p>Executes a <em>query</em> and returns an array where the value of each row is read as the given <em>type</em>.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_all(query,*args_,args:Array?=nil,astypes:NamedTuple)-instance-method" class="signature"><strong>#query_all</strong>(query, *args_, args : Array? = <span class="n">nil</span>, as types : NamedTuple)</a>
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<div class="summary"><p>Executes a <em>query</em> and returns an array where each row is read as a named tuple of the given <em>types</em> (the keys of the named tuple are not necessarily the column names).</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_all(query,*args_,args:Array?=nil,&block:ResultSet-%3EU):Array(U)forallU-instance-method" class="signature"><strong>#query_all</strong>(query, *args_, args : Array? = <span class="n">nil</span>, &block : ResultSet -> U) : Array(U) forall U</a>
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<div class="summary"><p>Executes a <em>query</em> and yield a <code><a href="../DB/ResultSet.html">ResultSet</a></code> positioned at the beginning of each row, returning an array of the values of the blocks.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_all(query,*args_,args:Array?=nil,astypes:Tuple)-instance-method" class="signature"><strong>#query_all</strong>(query, *args_, args : Array? = <span class="n">nil</span>, as types : Tuple)</a>
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<div class="summary"><p>Executes a <em>query</em> and returns an array where each row is read as a tuple of the given <em>types</em>.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_each(query,*args_,args:Array?=nil,&)-instance-method" class="signature"><strong>#query_each</strong>(query, *args_, args : Array? = <span class="n">nil</span>, &)</a>
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<div class="summary"><p>Executes a <em>query</em> and yields the <code><a href="../DB/ResultSet.html">ResultSet</a></code> once per each row.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_one(query,*args_,args:Array?=nil,&block:ResultSet-%3EU):UforallU-instance-method" class="signature"><strong>#query_one</strong>(query, *args_, args : Array? = <span class="n">nil</span>, &block : ResultSet -> U) : U forall U</a>
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<div class="summary"><p>Executes a <em>query</em> that expects a single row and yields a <code><a href="../DB/ResultSet.html">ResultSet</a></code> positioned at that first row.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_one(query,*args_,args:Array?=nil,astypes:Tuple)-instance-method" class="signature"><strong>#query_one</strong>(query, *args_, args : Array? = <span class="n">nil</span>, as types : Tuple)</a>
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<div class="summary"><p>Executes a <em>query</em> that expects a single row and returns it as a tuple of the given <em>types</em>.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_one(query,*args_,args:Array?=nil,astypes:NamedTuple)-instance-method" class="signature"><strong>#query_one</strong>(query, *args_, args : Array? = <span class="n">nil</span>, as types : NamedTuple)</a>
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<div class="summary"><p>Executes a <em>query</em> that expects a single row and returns it as a named tuple of the given <em>types</em> (the keys of the named tuple are not necessarily the column names).</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_one(query,*args_,args:Array?=nil,astype:Class)-instance-method" class="signature"><strong>#query_one</strong>(query, *args_, args : Array? = <span class="n">nil</span>, as type : Class)</a>
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<div class="summary"><p>Executes a <em>query</em> that expects a single row and returns the first column's value as the given <em>type</em>.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_one?(query,*args_,args:Array?=nil,astype:Class)-instance-method" class="signature"><strong>#query_one?</strong>(query, *args_, args : Array? = <span class="n">nil</span>, as type : Class)</a>
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<div class="summary"><p>Executes a <em>query</em> that expects a single row and returns the first column's value as the given <em>type</em>.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_one?(query,*args_,args:Array?=nil,astypes:NamedTuple)-instance-method" class="signature"><strong>#query_one?</strong>(query, *args_, args : Array? = <span class="n">nil</span>, as types : NamedTuple)</a>
|
|
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<div class="summary"><p>Executes a <em>query</em> that expects a single row and returns it as a named tuple of the given <em>types</em> (the keys of the named tuple are not necessarily the column names).</p></div>
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</li>
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<li class="entry-summary">
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<a href="#query_one?(query,*args_,args:Array?=nil,astypes:Tuple)-instance-method" class="signature"><strong>#query_one?</strong>(query, *args_, args : Array? = <span class="n">nil</span>, as types : Tuple)</a>
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<div class="summary"><p>Executes a <em>query</em> that expects a single row and returns it as a tuple of the given <em>types</em>.</p></div>
|
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</li>
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<li class="entry-summary">
|
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<a href="#query_one?(query,*args_,args:Array?=nil,&block:ResultSet-%3EU):U?forallU-instance-method" class="signature"><strong>#query_one?</strong>(query, *args_, args : Array? = <span class="n">nil</span>, &block : ResultSet -> U) : U? forall U</a>
|
|
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<div class="summary"><p>Executes a <em>query</em> that expects at most a single row and yields a <code><a href="../DB/ResultSet.html">ResultSet</a></code> positioned at that first row.</p></div>
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</li>
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<li class="entry-summary">
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<a href="#scalar(query,*args_,args:Array?=nil)-instance-method" class="signature"><strong>#scalar</strong>(query, *args_, args : Array? = <span class="n">nil</span>)</a>
|
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|
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<div class="summary"><p>Performs the <code><a href="../DB/QueryMethods.html#query(query,*args_,args:Array?=nil)-instance-method">#query</a></code> and returns a single scalar value</p></div>
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</li>
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</ul>
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<div class="methods-inherited">
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<h2>
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<a id="instance-method-detail" class="anchor" href="#instance-method-detail">
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<svg class="octicon-link" aria-hidden="true">
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<use href="#octicon-link"/>
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</svg>
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</a>
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Instance Method Detail
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</h2>
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<div class="entry-detail" id="exec(query,*args_,args:Array?=nil)-instance-method">
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<div class="signature">
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def <strong>exec</strong>(query, *args_, args : Array? = <span class="n">nil</span>)
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<a class="method-permalink" href="#exec(query,*args_,args:Array?=nil)-instance-method">#</a>
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</div>
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<div class="doc">
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<p>Performs the <code><a href="../DB/QueryMethods.html#query(query,*args_,args:Array?=nil)-instance-method">#query</a></code> and returns an <code><a href="../DB/ExecResult.html">ExecResult</a></code></p>
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</div>
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<br/>
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<div>
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[<a href="https://github.com/crystal-lang/crystal-db/blob/v0.10.1/src/db/query_methods.cr#L274" target="_blank">View source</a>]
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</div>
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</div>
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<div class="entry-detail" id="query(query,*args_,args:Array?=nil)-instance-method">
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<div class="signature">
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def <strong>query</strong>(query, *args_, args : Array? = <span class="n">nil</span>)
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<a class="method-permalink" href="#query(query,*args_,args:Array?=nil)-instance-method">#</a>
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</div>
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<div class="doc">
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<p>Executes a <em>query</em> and returns a <code><a href="../DB/ResultSet.html">ResultSet</a></code> with the results.
|
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The <code><a href="../DB/ResultSet.html">ResultSet</a></code> must be closed manually.</p>
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<pre><code class="language-crystal">result <span class="o">=</span> db.query <span class="s">"select name from contacts where id = ?"</span>, <span class="n">10</span>
|
|
<span class="k">begin</span>
|
|
<span class="k">if</span> result.move_next
|
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id <span class="o">=</span> result.read(<span class="t">Int32</span>)
|
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<span class="k">end</span>
|
|
<span class="k">ensure</span>
|
|
result.close
|
|
<span class="k">end</span></code></pre>
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<p>Note: to use a dynamic list length of arguments use <code>args:</code> keyword argument.</p>
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<pre><code class="language-crystal">result <span class="o">=</span> db.query <span class="s">"select name from contacts where id = ?"</span>, args: [<span class="n">10</span>]</code></pre>
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</div>
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<br/>
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<div>
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[<a href="https://github.com/crystal-lang/crystal-db/blob/v0.10.1/src/db/query_methods.cr#L45" target="_blank">View source</a>]
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</div>
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</div>
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<div class="entry-detail" id="query(query,*args_,args:Array?=nil,&)-instance-method">
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<div class="signature">
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def <strong>query</strong>(query, *args_, args : Array? = <span class="n">nil</span>, &)
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<a class="method-permalink" href="#query(query,*args_,args:Array?=nil,&)-instance-method">#</a>
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</div>
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<div class="doc">
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|
<p>Executes a <em>query</em> and yields a <code><a href="../DB/ResultSet.html">ResultSet</a></code> with the results.
|
|
The <code><a href="../DB/ResultSet.html">ResultSet</a></code> is closed automatically.</p>
|
|
|
|
<pre><code class="language-crystal">db.query(<span class="s">"select name from contacts where age > ?"</span>, <span class="n">18</span>) <span class="k">do</span> <span class="o">|</span>rs<span class="o">|</span>
|
|
rs.each <span class="k">do</span>
|
|
name <span class="o">=</span> rs.read(<span class="t">String</span>)
|
|
<span class="k">end</span>
|
|
<span class="k">end</span></code></pre>
|
|
</div>
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<br/>
|
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<div>
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|
[<a href="https://github.com/crystal-lang/crystal-db/blob/v0.10.1/src/db/query_methods.cr#L59" target="_blank">View source</a>]
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</div>
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</div>
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<div class="entry-detail" id="query_all(query,*args_,args:Array?=nil,astype:Class)-instance-method">
|
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<div class="signature">
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def <strong>query_all</strong>(query, *args_, args : Array? = <span class="n">nil</span>, as type : Class)
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<a class="method-permalink" href="#query_all(query,*args_,args:Array?=nil,astype:Class)-instance-method">#</a>
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</div>
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<div class="doc">
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<p>Executes a <em>query</em> and returns an array where the
|
|
value of each row is read as the given <em>type</em>.</p>
|
|
|
|
<pre><code class="language-crystal">names <span class="o">=</span> db.query_all <span class="s">"select name from contacts"</span>, <span class="k">as</span>: <span class="t">String</span></code></pre>
|
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</div>
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<br/>
|
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<div>
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|
[<a href="https://github.com/crystal-lang/crystal-db/blob/v0.10.1/src/db/query_methods.cr#L251" target="_blank">View source</a>]
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</div>
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</div>
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<div class="entry-detail" id="query_all(query,*args_,args:Array?=nil,astypes:NamedTuple)-instance-method">
|
|
<div class="signature">
|
|
|
|
def <strong>query_all</strong>(query, *args_, args : Array? = <span class="n">nil</span>, as types : NamedTuple)
|
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|
|
<a class="method-permalink" href="#query_all(query,*args_,args:Array?=nil,astypes:NamedTuple)-instance-method">#</a>
|
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</div>
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|
<div class="doc">
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|
|
|
<p>Executes a <em>query</em> and returns an array where each row is
|
|
read as a named tuple of the given <em>types</em> (the keys of the named tuple
|
|
are not necessarily the column names).</p>
|
|
|
|
<pre><code class="language-crystal">contacts <span class="o">=</span> db.query_all <span class="s">"select name, age from contacts"</span>, <span class="k">as</span>: {name: <span class="t">String</span>, age: <span class="t">Int32</span>}</code></pre>
|
|
</div>
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<br/>
|
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<div>
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|
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|
[<a href="https://github.com/crystal-lang/crystal-db/blob/v0.10.1/src/db/query_methods.cr#L239" target="_blank">View source</a>]
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</div>
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</div>
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|
<div class="entry-detail" id="query_all(query,*args_,args:Array?=nil,&block:ResultSet->U):Array(U)forallU-instance-method">
|
|
<div class="signature">
|
|
|
|
def <strong>query_all</strong>(query, *args_, args : Array? = <span class="n">nil</span>, &block : <a href="../DB/ResultSet.html">ResultSet</a> -> U) : Array(U) forall U
|
|
|
|
<a class="method-permalink" href="#query_all(query,*args_,args:Array?=nil,&block:ResultSet-%3EU):Array(U)forallU-instance-method">#</a>
|
|
</div>
|
|
|
|
<div class="doc">
|
|
|
|
<p>Executes a <em>query</em> and yield a <code><a href="../DB/ResultSet.html">ResultSet</a></code> positioned at the beginning
|
|
of each row, returning an array of the values of the blocks.</p>
|
|
|
|
<pre><code class="language-crystal">names <span class="o">=</span> db.query_all <span class="s">"select name from contacts"</span>, <span class="o">&</span>.read(<span class="t">String</span>)</code></pre>
|
|
</div>
|
|
|
|
<br/>
|
|
<div>
|
|
|
|
[<a href="https://github.com/crystal-lang/crystal-db/blob/v0.10.1/src/db/query_methods.cr#L212" target="_blank">View source</a>]
|
|
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|
</div>
|
|
</div>
|
|
|
|
<div class="entry-detail" id="query_all(query,*args_,args:Array?=nil,astypes:Tuple)-instance-method">
|
|
<div class="signature">
|
|
|
|
def <strong>query_all</strong>(query, *args_, args : Array? = <span class="n">nil</span>, as types : Tuple)
|
|
|
|
<a class="method-permalink" href="#query_all(query,*args_,args:Array?=nil,astypes:Tuple)-instance-method">#</a>
|
|
</div>
|
|
|
|
<div class="doc">
|
|
|
|
<p>Executes a <em>query</em> and returns an array where each row is
|
|
read as a tuple of the given <em>types</em>.</p>
|
|
|
|
<pre><code class="language-crystal">contacts <span class="o">=</span> db.query_all <span class="s">"select name, age from contacts"</span>, <span class="k">as</span>: {<span class="t">String</span>, <span class="t">Int32</span>}</code></pre>
|
|
</div>
|
|
|
|
<br/>
|
|
<div>
|
|
|
|
[<a href="https://github.com/crystal-lang/crystal-db/blob/v0.10.1/src/db/query_methods.cr#L226" target="_blank">View source</a>]
|
|
|
|
</div>
|
|
</div>
|
|
|
|
<div class="entry-detail" id="query_each(query,*args_,args:Array?=nil,&)-instance-method">
|
|
<div class="signature">
|
|
|
|
def <strong>query_each</strong>(query, *args_, args : Array? = <span class="n">nil</span>, &)
|
|
|
|
<a class="method-permalink" href="#query_each(query,*args_,args:Array?=nil,&)-instance-method">#</a>
|
|
</div>
|
|
|
|
<div class="doc">
|
|
|
|
<p>Executes a <em>query</em> and yields the <code><a href="../DB/ResultSet.html">ResultSet</a></code> once per each row.
|
|
The <code><a href="../DB/ResultSet.html">ResultSet</a></code> is closed automatically.</p>
|
|
|
|
<pre><code class="language-crystal">db.query_each <span class="s">"select name from contacts"</span> <span class="k">do</span> <span class="o">|</span>rs<span class="o">|</span>
|
|
puts rs.read(<span class="t">String</span>)
|
|
<span class="k">end</span></code></pre>
|
|
</div>
|
|
|
|
<br/>
|
|
<div>
|
|
|
|
[<a href="https://github.com/crystal-lang/crystal-db/blob/v0.10.1/src/db/query_methods.cr#L265" target="_blank">View source</a>]
|
|
|
|
</div>
|
|
</div>
|
|
|
|
<div class="entry-detail" id="query_one(query,*args_,args:Array?=nil,&block:ResultSet->U):UforallU-instance-method">
|
|
<div class="signature">
|
|
|
|
def <strong>query_one</strong>(query, *args_, args : Array? = <span class="n">nil</span>, &block : <a href="../DB/ResultSet.html">ResultSet</a> -> U) : U forall U
|
|
|
|
<a class="method-permalink" href="#query_one(query,*args_,args:Array?=nil,&block:ResultSet-%3EU):UforallU-instance-method">#</a>
|
|
</div>
|
|
|
|
<div class="doc">
|
|
|
|
<p>Executes a <em>query</em> that expects a single row and yields a <code><a href="../DB/ResultSet.html">ResultSet</a></code>
|
|
positioned at that first row.</p>
|
|
|
|
<p>The given block must not invoke <code>move_next</code> on the yielded result set.</p>
|
|
|
|
<p>Raises <code><a href="../DB/NoResultsError.html">DB::NoResultsError</a></code> if there were no rows.
|
|
Raises <code><a href="../DB/Error.html">DB::Error</a></code> if there were more than one row.</p>
|
|
|
|
<pre><code class="language-crystal">name <span class="o">=</span> db.query_one <span class="s">"select name from contacts where id = ?"</span>, <span class="n">18</span>, <span class="o">&</span>.read(<span class="t">String</span>)</code></pre>
|
|
</div>
|
|
|
|
<br/>
|
|
<div>
|
|
|
|
[<a href="https://github.com/crystal-lang/crystal-db/blob/v0.10.1/src/db/query_methods.cr#L76" target="_blank">View source</a>]
|
|
|
|
</div>
|
|
</div>
|
|
|
|
<div class="entry-detail" id="query_one(query,*args_,args:Array?=nil,astypes:Tuple)-instance-method">
|
|
<div class="signature">
|
|
|
|
def <strong>query_one</strong>(query, *args_, args : Array? = <span class="n">nil</span>, as types : Tuple)
|
|
|
|
<a class="method-permalink" href="#query_one(query,*args_,args:Array?=nil,astypes:Tuple)-instance-method">#</a>
|
|
</div>
|
|
|
|
<div class="doc">
|
|
|
|
<p>Executes a <em>query</em> that expects a single row and returns it
|
|
as a tuple of the given <em>types</em>.</p>
|
|
|
|
<p>Raises <code><a href="../DB/NoResultsError.html">DB::NoResultsError</a></code> if there were no rows.
|
|
Raises <code><a href="../DB/Error.html">DB::Error</a></code> if there were more than one row.</p>
|
|
|
|
<pre><code class="language-crystal">db.query_one <span class="s">"select name, age from contacts where id = ?"</span>, <span class="n">1</span>, <span class="k">as</span>: {<span class="t">String</span>, <span class="t">Int32</span>}</code></pre>
|
|
</div>
|
|
|
|
<br/>
|
|
<div>
|
|
|
|
[<a href="https://github.com/crystal-lang/crystal-db/blob/v0.10.1/src/db/query_methods.cr#L95" target="_blank">View source</a>]
|
|
|
|
</div>
|
|
</div>
|
|
|
|
<div class="entry-detail" id="query_one(query,*args_,args:Array?=nil,astypes:NamedTuple)-instance-method">
|
|
<div class="signature">
|
|
|
|
def <strong>query_one</strong>(query, *args_, args : Array? = <span class="n">nil</span>, as types : NamedTuple)
|
|
|
|
<a class="method-permalink" href="#query_one(query,*args_,args:Array?=nil,astypes:NamedTuple)-instance-method">#</a>
|
|
</div>
|
|
|
|
<div class="doc">
|
|
|
|
<p>Executes a <em>query</em> that expects a single row and returns it
|
|
as a named tuple of the given <em>types</em> (the keys of the named tuple
|
|
are not necessarily the column names).</p>
|
|
|
|
<p>Raises <code><a href="../DB/NoResultsError.html">DB::NoResultsError</a></code> if there were no rows.
|
|
Raises <code><a href="../DB/Error.html">DB::Error</a></code> if there were more than one row.</p>
|
|
|
|
<pre><code class="language-crystal">db.query_one <span class="s">"select name, age from contacts where id = ?"</span>, <span class="n">1</span>, <span class="k">as</span>: {name: <span class="t">String</span>, age: <span class="t">Int32</span>}</code></pre>
|
|
</div>
|
|
|
|
<br/>
|
|
<div>
|
|
|
|
[<a href="https://github.com/crystal-lang/crystal-db/blob/v0.10.1/src/db/query_methods.cr#L111" target="_blank">View source</a>]
|
|
|
|
</div>
|
|
</div>
|
|
|
|
<div class="entry-detail" id="query_one(query,*args_,args:Array?=nil,astype:Class)-instance-method">
|
|
<div class="signature">
|
|
|
|
def <strong>query_one</strong>(query, *args_, args : Array? = <span class="n">nil</span>, as type : Class)
|
|
|
|
<a class="method-permalink" href="#query_one(query,*args_,args:Array?=nil,astype:Class)-instance-method">#</a>
|
|
</div>
|
|
|
|
<div class="doc">
|
|
|
|
<p>Executes a <em>query</em> that expects a single row
|
|
and returns the first column's value as the given <em>type</em>.</p>
|
|
|
|
<p>Raises <code><a href="../DB/NoResultsError.html">DB::NoResultsError</a></code> if there were no rows.
|
|
Raises <code><a href="../DB/Error.html">DB::Error</a></code> if there were more than one row.</p>
|
|
|
|
<pre><code class="language-crystal">db.query_one <span class="s">"select name from contacts where id = ?"</span>, <span class="n">1</span>, <span class="k">as</span>: <span class="t">String</span></code></pre>
|
|
</div>
|
|
|
|
<br/>
|
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<div>
|
|
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[<a href="https://github.com/crystal-lang/crystal-db/blob/v0.10.1/src/db/query_methods.cr#L126" target="_blank">View source</a>]
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</div>
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</div>
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<div class="entry-detail" id="query_one?(query,*args_,args:Array?=nil,astype:Class)-instance-method">
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<div class="signature">
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def <strong>query_one?</strong>(query, *args_, args : Array? = <span class="n">nil</span>, as type : Class)
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<a class="method-permalink" href="#query_one?(query,*args_,args:Array?=nil,astype:Class)-instance-method">#</a>
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</div>
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<div class="doc">
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<p>Executes a <em>query</em> that expects a single row
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and returns the first column's value as the given <em>type</em>.</p>
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<p>Returns <code>nil</code> if there were no rows.</p>
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<p>Raises <code><a href="../DB/Error.html">DB::Error</a></code> if there were more than one row.</p>
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<pre><code class="language-crystal">name <span class="o">=</span> db.query_one? <span class="s">"select name from contacts where id = ?"</span>, <span class="n">1</span>, <span class="k">as</span>: <span class="t">String</span>
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<span class="k">typeof</span>(name) <span class="c"># => String?</span></code></pre>
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</div>
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<br/>
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<div>
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[<a href="https://github.com/crystal-lang/crystal-db/blob/v0.10.1/src/db/query_methods.cr#L200" target="_blank">View source</a>]
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</div>
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</div>
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<div class="entry-detail" id="query_one?(query,*args_,args:Array?=nil,astypes:NamedTuple)-instance-method">
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<div class="signature">
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def <strong>query_one?</strong>(query, *args_, args : Array? = <span class="n">nil</span>, as types : NamedTuple)
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<a class="method-permalink" href="#query_one?(query,*args_,args:Array?=nil,astypes:NamedTuple)-instance-method">#</a>
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</div>
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<div class="doc">
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<p>Executes a <em>query</em> that expects a single row and returns it
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as a named tuple of the given <em>types</em> (the keys of the named tuple
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are not necessarily the column names).</p>
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<p>Returns <code>nil</code> if there were no rows.</p>
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<p>Raises <code><a href="../DB/Error.html">DB::Error</a></code> if there were more than one row.</p>
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<pre><code class="language-crystal">result <span class="o">=</span> db.query_one? <span class="s">"select name, age from contacts where id = ?"</span>, <span class="n">1</span>, <span class="k">as</span>: {age: <span class="t">String</span>, name: <span class="t">Int32</span>}
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<span class="k">typeof</span>(result) <span class="c"># => NamedTuple(age: String, name: Int32) | Nil</span></code></pre>
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</div>
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<br/>
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<div>
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[<a href="https://github.com/crystal-lang/crystal-db/blob/v0.10.1/src/db/query_methods.cr#L183" target="_blank">View source</a>]
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</div>
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</div>
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<div class="entry-detail" id="query_one?(query,*args_,args:Array?=nil,astypes:Tuple)-instance-method">
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<div class="signature">
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def <strong>query_one?</strong>(query, *args_, args : Array? = <span class="n">nil</span>, as types : Tuple)
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<a class="method-permalink" href="#query_one?(query,*args_,args:Array?=nil,astypes:Tuple)-instance-method">#</a>
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</div>
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<div class="doc">
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<p>Executes a <em>query</em> that expects a single row and returns it
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as a tuple of the given <em>types</em>.</p>
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<p>Returns <code>nil</code> if there were no rows.</p>
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<p>Raises <code><a href="../DB/Error.html">DB::Error</a></code> if there were more than one row.</p>
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<pre><code class="language-crystal">result <span class="o">=</span> db.query_one? <span class="s">"select name, age from contacts where id = ?"</span>, <span class="n">1</span>, <span class="k">as</span>: {<span class="t">String</span>, <span class="t">Int32</span>}
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<span class="k">typeof</span>(result) <span class="c"># => Tuple(String, Int32) | Nil</span></code></pre>
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</div>
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<br/>
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<div>
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[<a href="https://github.com/crystal-lang/crystal-db/blob/v0.10.1/src/db/query_methods.cr#L165" target="_blank">View source</a>]
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</div>
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</div>
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<div class="entry-detail" id="query_one?(query,*args_,args:Array?=nil,&block:ResultSet->U):U?forallU-instance-method">
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<div class="signature">
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def <strong>query_one?</strong>(query, *args_, args : Array? = <span class="n">nil</span>, &block : <a href="../DB/ResultSet.html">ResultSet</a> -> U) : U? forall U
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<a class="method-permalink" href="#query_one?(query,*args_,args:Array?=nil,&block:ResultSet-%3EU):U?forallU-instance-method">#</a>
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</div>
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<div class="doc">
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<p>Executes a <em>query</em> that expects at most a single row and yields a <code><a href="../DB/ResultSet.html">ResultSet</a></code>
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positioned at that first row.</p>
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<p>Returns <code>nil</code>, not invoking the block, if there were no rows.</p>
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<p>Raises <code><a href="../DB/Error.html">DB::Error</a></code> if there were more than one row
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(this ends up invoking the block once).</p>
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<pre><code class="language-crystal">name <span class="o">=</span> db.query_one? <span class="s">"select name from contacts where id = ?"</span>, <span class="n">18</span>, <span class="o">&</span>.read(<span class="t">String</span>)
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<span class="k">typeof</span>(name) <span class="c"># => String | Nil</span></code></pre>
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</div>
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<br/>
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<div>
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[<a href="https://github.com/crystal-lang/crystal-db/blob/v0.10.1/src/db/query_methods.cr#L144" target="_blank">View source</a>]
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</div>
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</div>
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<div class="entry-detail" id="scalar(query,*args_,args:Array?=nil)-instance-method">
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<div class="signature">
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def <strong>scalar</strong>(query, *args_, args : Array? = <span class="n">nil</span>)
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<a class="method-permalink" href="#scalar(query,*args_,args:Array?=nil)-instance-method">#</a>
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</div>
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<div class="doc">
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<p>Performs the <code><a href="../DB/QueryMethods.html#query(query,*args_,args:Array?=nil)-instance-method">#query</a></code> and returns a single scalar value</p>
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<pre><code class="language-crystal">puts db.scalar(<span class="s">"SELECT MAX(name)"</span>).<span class="k">as</span>(<span class="t">String</span>) <span class="c"># => (a String)</span></code></pre>
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</div>
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<br/>
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<div>
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[<a href="https://github.com/crystal-lang/crystal-db/blob/v0.10.1/src/db/query_methods.cr#L283" target="_blank">View source</a>]
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</div>
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</div>
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