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<h1 class="heading"><a href="../index.html">
<span>Presto 0.184 Documentation</span></a></h1>
<h2 class="heading"><span>6.8. String Functions and Operators</span></h2>
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<div class="section" id="string-functions-and-operators">
<h1>6.8. String Functions and Operators</h1>
<div class="section" id="string-operators">
<h2>String Operators</h2>
<p>The <code class="docutils literal"><span class="pre">||</span></code> operator performs concatenation.</p>
</div>
<div class="section" id="string-functions">
<h2>String Functions</h2>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p>These functions assume that the input strings contain valid UTF-8 encoded
Unicode code points. There are no explicit checks for valid UTF-8 and
the functions may return incorrect results on invalid UTF-8.
Invalid UTF-8 data can be corrected with <a class="reference internal" href="#from_utf8" title="from_utf8"><code class="xref py py-func docutils literal"><span class="pre">from_utf8()</span></code></a>.</p>
<p>Additionally, the functions operate on Unicode code points and not user
visible <em>characters</em> (or <em>grapheme clusters</em>). Some languages combine
multiple code points into a single user-perceived <em>character</em>, the basic
unit of a writing system for a language, but the functions will treat each
code point as a separate unit.</p>
<p class="last">The <a class="reference internal" href="#lower" title="lower"><code class="xref py py-func docutils literal"><span class="pre">lower()</span></code></a> and <a class="reference internal" href="#upper" title="upper"><code class="xref py py-func docutils literal"><span class="pre">upper()</span></code></a> functions do not perform
locale-sensitive, context-sensitive, or one-to-many mappings required for
some languages. Specifically, this will return incorrect results for
Lithuanian, Turkish and Azeri.</p>
</div>
<dl class="function">
<dt id="chr">
<code class="descname">chr</code><span class="sig-paren">(</span><em>n</em><span class="sig-paren">)</span> → varchar</dt>
<dd><p>Returns the Unicode code point <code class="docutils literal"><span class="pre">n</span></code> as a single character string.</p>
</dd></dl>
<dl class="function">
<dt id="codepoint">
<code class="descname">codepoint</code><span class="sig-paren">(</span><em>string</em><span class="sig-paren">)</span> → integer</dt>
<dd><p>Returns the Unicode code point of the only character of <code class="docutils literal"><span class="pre">string</span></code>.</p>
</dd></dl>
<dl class="function">
<dt id="concat">
<code class="descname">concat</code><span class="sig-paren">(</span><em>string1</em>, <em>...</em>, <em>stringN</em><span class="sig-paren">)</span> → varchar</dt>
<dd><p>Returns the concatenation of <code class="docutils literal"><span class="pre">string1</span></code>, <code class="docutils literal"><span class="pre">string2</span></code>, <code class="docutils literal"><span class="pre">...</span></code>, <code class="docutils literal"><span class="pre">stringN</span></code>.
This function provides the same functionality as the
SQL-standard concatenation operator (<code class="docutils literal"><span class="pre">||</span></code>).</p>
</dd></dl>
<dl class="function">
<dt id="hamming_distance">
<code class="descname">hamming_distance</code><span class="sig-paren">(</span><em>string1</em>, <em>string2</em><span class="sig-paren">)</span> → bigint</dt>
<dd><p>Returns the Hamming distance of <code class="docutils literal"><span class="pre">string1</span></code> and <code class="docutils literal"><span class="pre">string2</span></code>,
i.e. the number of positions at which the corresponding characters are different.
Note that the two strings must have the same length.</p>
</dd></dl>
<dl class="function">
<dt id="length">
<code class="descname">length</code><span class="sig-paren">(</span><em>string</em><span class="sig-paren">)</span> → bigint</dt>
<dd><p>Returns the length of <code class="docutils literal"><span class="pre">string</span></code> in characters.</p>
</dd></dl>
<dl class="function">
<dt id="levenshtein_distance">
<code class="descname">levenshtein_distance</code><span class="sig-paren">(</span><em>string1</em>, <em>string2</em><span class="sig-paren">)</span> → bigint</dt>
<dd><p>Returns the Levenshtein edit distance of <code class="docutils literal"><span class="pre">string1</span></code> and <code class="docutils literal"><span class="pre">string2</span></code>,
i.e. the minimum number of single-character edits (insertions,
deletions or substitutions) needed to change <code class="docutils literal"><span class="pre">string1</span></code> into <code class="docutils literal"><span class="pre">string2</span></code>.</p>
</dd></dl>
<dl class="function">
<dt id="lower">
<code class="descname">lower</code><span class="sig-paren">(</span><em>string</em><span class="sig-paren">)</span> → varchar</dt>
<dd><p>Converts <code class="docutils literal"><span class="pre">string</span></code> to lowercase.</p>
</dd></dl>
<dl class="function">
<dt id="lpad">
<code class="descname">lpad</code><span class="sig-paren">(</span><em>string</em>, <em>size</em>, <em>padstring</em><span class="sig-paren">)</span> → varchar</dt>
<dd><p>Left pads <code class="docutils literal"><span class="pre">string</span></code> to <code class="docutils literal"><span class="pre">size</span></code> characters with <code class="docutils literal"><span class="pre">padstring</span></code>.
If <code class="docutils literal"><span class="pre">size</span></code> is less than the length of <code class="docutils literal"><span class="pre">string</span></code>, the result is
truncated to <code class="docutils literal"><span class="pre">size</span></code> characters. <code class="docutils literal"><span class="pre">size</span></code> must not be negative
and <code class="docutils literal"><span class="pre">padstring</span></code> must be non-empty.</p>
</dd></dl>
<dl class="function">
<dt id="ltrim">
<code class="descname">ltrim</code><span class="sig-paren">(</span><em>string</em><span class="sig-paren">)</span> → varchar</dt>
<dd><p>Removes leading whitespace from <code class="docutils literal"><span class="pre">string</span></code>.</p>
</dd></dl>
<dl class="function">
<dt id="replace">
<code class="descname">replace</code><span class="sig-paren">(</span><em>string</em>, <em>search</em><span class="sig-paren">)</span> → varchar</dt>
<dd><p>Removes all instances of <code class="docutils literal"><span class="pre">search</span></code> from <code class="docutils literal"><span class="pre">string</span></code>.</p>
</dd></dl>
<dl class="function">
<dt>
<code class="descname">replace</code><span class="sig-paren">(</span><em>string</em>, <em>search</em>, <em>replace</em><span class="sig-paren">)</span> → varchar</dt>
<dd><p>Replaces all instances of <code class="docutils literal"><span class="pre">search</span></code> with <code class="docutils literal"><span class="pre">replace</span></code> in <code class="docutils literal"><span class="pre">string</span></code>.</p>
</dd></dl>
<dl class="function">
<dt id="reverse">
<code class="descname">reverse</code><span class="sig-paren">(</span><em>string</em><span class="sig-paren">)</span> → varchar</dt>
<dd><p>Returns <code class="docutils literal"><span class="pre">string</span></code> with the characters in reverse order.</p>
</dd></dl>
<dl class="function">
<dt id="rpad">
<code class="descname">rpad</code><span class="sig-paren">(</span><em>string</em>, <em>size</em>, <em>padstring</em><span class="sig-paren">)</span> → varchar</dt>
<dd><p>Right pads <code class="docutils literal"><span class="pre">string</span></code> to <code class="docutils literal"><span class="pre">size</span></code> characters with <code class="docutils literal"><span class="pre">padstring</span></code>.
If <code class="docutils literal"><span class="pre">size</span></code> is less than the length of <code class="docutils literal"><span class="pre">string</span></code>, the result is
truncated to <code class="docutils literal"><span class="pre">size</span></code> characters. <code class="docutils literal"><span class="pre">size</span></code> must not be negative
and <code class="docutils literal"><span class="pre">padstring</span></code> must be non-empty.</p>
</dd></dl>
<dl class="function">
<dt id="rtrim">
<code class="descname">rtrim</code><span class="sig-paren">(</span><em>string</em><span class="sig-paren">)</span> → varchar</dt>
<dd><p>Removes trailing whitespace from <code class="docutils literal"><span class="pre">string</span></code>.</p>
</dd></dl>
<dl class="function">
<dt id="split">
<code class="descname">split</code><span class="sig-paren">(</span><em>string</em>, <em>delimiter</em><span class="sig-paren">)</span> → array<varchar></dt>
<dd><p>Splits <code class="docutils literal"><span class="pre">string</span></code> on <code class="docutils literal"><span class="pre">delimiter</span></code> and returns an array.</p>
</dd></dl>
<dl class="function">
<dt>
<code class="descname">split</code><span class="sig-paren">(</span><em>string</em>, <em>delimiter</em>, <em>limit</em><span class="sig-paren">)</span> → array<varchar></dt>
<dd><p>Splits <code class="docutils literal"><span class="pre">string</span></code> on <code class="docutils literal"><span class="pre">delimiter</span></code> and returns an array of size at most
<code class="docutils literal"><span class="pre">limit</span></code>. The last element in the array always contain everything
left in the <code class="docutils literal"><span class="pre">string</span></code>. <code class="docutils literal"><span class="pre">limit</span></code> must be a positive number.</p>
</dd></dl>
<dl class="function">
<dt id="split_part">
<code class="descname">split_part</code><span class="sig-paren">(</span><em>string</em>, <em>delimiter</em>, <em>index</em><span class="sig-paren">)</span> → varchar</dt>
<dd><p>Splits <code class="docutils literal"><span class="pre">string</span></code> on <code class="docutils literal"><span class="pre">delimiter</span></code> and returns the field <code class="docutils literal"><span class="pre">index</span></code>.
Field indexes start with <code class="docutils literal"><span class="pre">1</span></code>. If the index is larger than than
the number of fields, then null is returned.</p>
</dd></dl>
<dl class="function">
<dt id="split_to_map">
<code class="descname">split_to_map</code><span class="sig-paren">(</span><em>string</em>, <em>entryDelimiter</em>, <em>keyValueDelimiter</em><span class="sig-paren">)</span> → map<varchar, varchar></dt>
<dd><p>Splits <code class="docutils literal"><span class="pre">string</span></code> by <code class="docutils literal"><span class="pre">entryDelimiter</span></code> and <code class="docutils literal"><span class="pre">keyValueDelimiter</span></code> and returns a map.
<code class="docutils literal"><span class="pre">entryDelimiter</span></code> splits <code class="docutils literal"><span class="pre">string</span></code> into key-value pairs. <code class="docutils literal"><span class="pre">keyValueDelimiter</span></code> splits
each pair into key and value.</p>
</dd></dl>
<dl class="function">
<dt id="strpos">
<code class="descname">strpos</code><span class="sig-paren">(</span><em>string</em>, <em>substring</em><span class="sig-paren">)</span> → bigint</dt>
<dd><p>Returns the starting position of the first instance of <code class="docutils literal"><span class="pre">substring</span></code> in
<code class="docutils literal"><span class="pre">string</span></code>. Positions start with <code class="docutils literal"><span class="pre">1</span></code>. If not found, <code class="docutils literal"><span class="pre">0</span></code> is returned.</p>
</dd></dl>
<dl class="function">
<dt id="position">
<code class="descname">position</code><span class="sig-paren">(</span><em>substring IN string</em><span class="sig-paren">)</span> → bigint</dt>
<dd><p>Returns the starting position of the first instance of <code class="docutils literal"><span class="pre">substring</span></code> in
<code class="docutils literal"><span class="pre">string</span></code>. Positions start with <code class="docutils literal"><span class="pre">1</span></code>. If not found, <code class="docutils literal"><span class="pre">0</span></code> is returned.</p>
</dd></dl>
<dl class="function">
<dt id="substr">
<code class="descname">substr</code><span class="sig-paren">(</span><em>string</em>, <em>start</em><span class="sig-paren">)</span> → varchar</dt>
<dd><p>Returns the rest of <code class="docutils literal"><span class="pre">string</span></code> from the starting position <code class="docutils literal"><span class="pre">start</span></code>.
Positions start with <code class="docutils literal"><span class="pre">1</span></code>. A negative starting position is interpreted
as being relative to the end of the string.</p>
</dd></dl>
<dl class="function">
<dt>
<code class="descname">substr</code><span class="sig-paren">(</span><em>string</em>, <em>start</em>, <em>length</em><span class="sig-paren">)</span> → varchar</dt>
<dd><p>Returns a substring from <code class="docutils literal"><span class="pre">string</span></code> of length <code class="docutils literal"><span class="pre">length</span></code> from the starting
position <code class="docutils literal"><span class="pre">start</span></code>. Positions start with <code class="docutils literal"><span class="pre">1</span></code>. A negative starting
position is interpreted as being relative to the end of the string.</p>
</dd></dl>
<dl class="function">
<dt id="trim">
<code class="descname">trim</code><span class="sig-paren">(</span><em>string</em><span class="sig-paren">)</span> → varchar</dt>
<dd><p>Removes leading and trailing whitespace from <code class="docutils literal"><span class="pre">string</span></code>.</p>
</dd></dl>
<dl class="function">
<dt id="upper">
<code class="descname">upper</code><span class="sig-paren">(</span><em>string</em><span class="sig-paren">)</span> → varchar</dt>
<dd><p>Converts <code class="docutils literal"><span class="pre">string</span></code> to uppercase.</p>
</dd></dl>
</div>
<div class="section" id="unicode-functions">
<h2>Unicode Functions</h2>
<dl class="function">
<dt id="normalize">
<code class="descname">normalize</code><span class="sig-paren">(</span><em>string</em><span class="sig-paren">)</span> → varchar</dt>
<dd><p>Transforms <code class="docutils literal"><span class="pre">string</span></code> with NFC normalization form.</p>
</dd></dl>
<dl class="function">
<dt>
<code class="descname">normalize</code><span class="sig-paren">(</span><em>string</em>, <em>form</em><span class="sig-paren">)</span> → varchar</dt>
<dd><p>Transforms <code class="docutils literal"><span class="pre">string</span></code> with the specified normalization form.
<code class="docutils literal"><span class="pre">form</span></code> must be be one of the following keywords:</p>
<table border="1" class="docutils">
<colgroup>
<col width="11%" />
<col width="89%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Form</th>
<th class="head">Description</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="docutils literal"><span class="pre">NFD</span></code></td>
<td>Canonical Decomposition</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal"><span class="pre">NFC</span></code></td>
<td>Canonical Decomposition, followed by Canonical Composition</td>
</tr>
<tr class="row-even"><td><code class="docutils literal"><span class="pre">NFKD</span></code></td>
<td>Compatibility Decomposition</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal"><span class="pre">NFKC</span></code></td>
<td>Compatibility Decomposition, followed by Canonical Composition</td>
</tr>
</tbody>
</table>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">This SQL-standard function has special syntax and requires
specifying <code class="docutils literal"><span class="pre">form</span></code> as a keyword, not as a string.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="to_utf8">
<code class="descname">to_utf8</code><span class="sig-paren">(</span><em>string</em><span class="sig-paren">)</span> → varbinary</dt>
<dd><p>Encodes <code class="docutils literal"><span class="pre">string</span></code> into a UTF-8 varbinary representation.</p>
</dd></dl>
<dl class="function">
<dt id="from_utf8">
<code class="descname">from_utf8</code><span class="sig-paren">(</span><em>binary</em><span class="sig-paren">)</span> → varchar</dt>
<dd><p>Decodes a UTF-8 encoded string from <code class="docutils literal"><span class="pre">binary</span></code>. Invalid UTF-8 sequences
are replaced with the Unicode replacement character <code class="docutils literal"><span class="pre">U+FFFD</span></code>.</p>
</dd></dl>
<dl class="function">
<dt>
<code class="descname">from_utf8</code><span class="sig-paren">(</span><em>binary</em>, <em>replace</em><span class="sig-paren">)</span> → varchar</dt>
<dd><p>Decodes a UTF-8 encoded string from <code class="docutils literal"><span class="pre">binary</span></code>. Invalid UTF-8 sequences
are replaced with <cite>replace</cite>. The replacement string <cite>replace</cite> must either
be a single character or empty (in which case invalid characters are
removed).</p>
</dd></dl>
</div>
</div>
</div>
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