163 lines
5.8 KiB
HTML
163 lines
5.8 KiB
HTML
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The COMPLETION() Table-Valued Function
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<h1 id="overview"><span>1. </span>Overview</h1>
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<p>The COMPLETION extension implements a <a href="vtab.html#tabfunc2">table-valued function</a> named
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"completion" that can be used to suggest completions of partially entered
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words during interactive SQL input. The completion table can be
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used to help implement tab-completion, for example.
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</p><h1 id="details"><span>2. </span>Details</h1>
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<p>The designed query interface is:
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</p><div class="codeblock"><pre>SELECT DISTINCT candidate COLLATE nocase
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FROM completion($prefix, $wholeline)
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ORDER BY 1;
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</pre></div>
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<p>The query above will return suggestions for the whole input word that
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begins with $prefix. The $wholeline parameter is all text from the beginning
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of the line up to the insertion point. The $wholeline parameter is used
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for context.
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</p><p>The $prefix parameter may be NULL, in which case the prefix is deduced
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from $wholeline. Or, the $wholeline parameter may be NULL or omitted if
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context information is unavailable or if context-aware completion is not
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desired.
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</p><p>The completion table might return the same candidate more than once, and
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it will return candidates in an arbitrary order. The DISTINCT keyword and
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the ORDER BY in the sample query above are added to make the answers unique
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and in lexicographical order.
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</p><h2 id="example_usage"><span>2.1. </span>Example Usage</h2>
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<p>The completion table is used to implement tab-completion in the
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<a href="cli.html">command-line shell</a> in conjunction with either the readline or linenoise
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input line editing packages for unix. See the
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<a href="https://sqlite.org/src/file/src/shell.c.in">https://sqlite.org/src/file/src/shell.c.in</a> source file for example
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code. Search for "FROM completion" to find the relevant code sections.
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</p><p>Because the completion table is built into the command-line shell in order
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to provide for tab-completions, you can run test queries against the
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completion table directly in the command-line shell. Simply type a
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query such as the example shown above, filling in appropriate values
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for $prefix and $wholeline, and observe the output.
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</p><h1 id="limitations"><span>3. </span>Limitations</h1>
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<p>The completion table is designed for interactive use. It will return
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answers at a speed appropriate for human typing. No effort is made to
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be unusually efficient, so long as the response time is nearly instantaneous
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in a user interface.
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</p><p>As of this writing (2017-07-13), the completion virtual table only
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looks for SQL keywords, and schema, table, and column names. The
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context contained in $wholeline is completely ignored. Future enhancements
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will try to return new completions taken from function and pragma names
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and other sources, as well as consider more context. The completion
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table should be considered a work-in-progress.
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</p>
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