216 lines
7.9 KiB
HTML
216 lines
7.9 KiB
HTML
<!DOCTYPE html>
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<html><head>
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<link href="sqlite.css" rel="stylesheet">
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<title>The CSV Virtual Table</title>
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</head>
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<body>
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Small. Fast. Reliable.<br>Choose any three.
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<div class=fancy>
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<div class=nosearch>
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<div class="fancy_title">
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The CSV Virtual Table
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</div>
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</div>
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<h1 id="overview"><span>1. </span>Overview</h1>
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<p>
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The CSV virtual table reads
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<a href="https://www.ietf.org/rfc/rfc4180.txt">RFC 4180</a> formatted comma-separated
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values, and returns that content as if it were rows and columns of an SQL
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table.
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</p>
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<p>
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The CSV virtual table is useful to applications that need to bulk-load
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large amounts of comma-separated value content.
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The CSV virtual table is also useful as a template source file for
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implementing other virtual tables.
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</p>
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<p>
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The CSV virtual table is not built into the SQLite amalgamation.
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It is available as a
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<a href="https://www.sqlite.org/src/artifact?ci=trunk&filename=ext/misc/csv.c">separate source file</a>
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that can be compiled into a <a href="loadext.html">loadable extension</a>.
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Typical usage of the CSV virtual table from the
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<a href="cli.html">command-line shell</a> would be something like this:
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</p><div class="codeblock"><pre>.load ./csv
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CREATE VIRTUAL TABLE temp.t1 USING csv(filename='thefile.csv');
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SELECT * FROM t1;
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</pre></div>
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<p>
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The first line of the script above causes the <a href="cli.html">command-line shell</a> to
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read and activate the run-time loadable extension for CSV. For an
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application, the equivalent C-language API is
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<a href="c3ref/load_extension.html">sqlite3_load_extension()</a>.
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Observe that the filename extension (ex: ".dll" or ".so" or ".dylib") is
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omitted from the extension filename. Omitting the filename extension is
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not required, but it helps in making the script cross-platform. SQLite
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will automatically append the appropriate extension.
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</p><p>
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The second line above creates a virtual table named "t1" that reads
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the content of the file named in the argument. The number and names of
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the columns is determined automatically by reading the first line of
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content. Other options to the CSV virtual table provide the ability to
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take the CSV content from a string rather than a separate file, and give
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the programmer more control over the number and names of the columns.
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The options are detailed below. The CSV virtual table is usually
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created as a TEMP table so that it exists only for the current database
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connection and does not become a permanent part of the database schema.
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Note that there is no "CREATE TEMP VIRTUAL TABLE" command in SQLite.
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Instead, prepend the "temp." schema prefix to the name of the virtual
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table.
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</p><p>
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The third line of the example shows the virtual table being used, to read
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all content of the CSV file. This is perhaps the simplest possible use
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of the virtual table. The CSV virtual table can be used anywhere an ordinary
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virtual table can be used. One can use the CSV virtual table inside subqueries,
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or <a href="lang_with.html">common table expressions</a> or add WHERE, GROUP BY, HAVING, ORDER BY,
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and LIMIT clauses as required.
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</p><h1 id="arguments"><span>2. </span>Arguments</h1>
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<p>
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The example above showed a single <b>filename='thefile.csv'</b> argument
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for the CSV virtual table. But other arguments are also possible.
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</p><ul>
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<li><p><b>filename=</b><i>FILENAME</i>
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</p><p>The <b>filename=</b> argument specifies an external file from which
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CSV content is read. Every CSV virtual table must have either a
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<b>filename=</b> argument or a <b>data=</b> argument and not both.
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</p></li><li><p><b>data=</b><i>TEXT</i>
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</p><p>The <b>data=</b> argument specifies that <i>TEXT</i> is the literal
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content of the CSV file.
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</p></li><li><p><b>schema=</b><i>SCHEMA</i>
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</p><p> The <b>schema=</b> argument specifies a <a href="lang_createtable.html">CREATE TABLE</a> statement that
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the CSV virtual table passes to the <a href="c3ref/declare_vtab.html">sqlite3_declare_vtab()</a> interface in
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order to define the names of the columns in the virtual table.
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</p></li><li><p><b>columns=</b><i>N</i>
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</p><p>The <b>columns=</b><i>N</i> argument specifies the number of columns
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in the CSV file.
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If the input data contains more columns than this,
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then the excess columns are ignored. If the input data contains fewer columns,
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then extra columns are filled with NULL.
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If the <b>columns=</b><i>N</i> argument is omitted, the first line of the
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CSV file is read to determine the number of columns.
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</p></li><li><p><b>header=</b><i>BOOLEAN</i><br>
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or just<br>
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<b>header</b>
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</p><p>If the <b>header</b> argument is true then the first row of the CSV file
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to be treated as a header rather than as data. The second line of the CSV
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file becomes the first row of content.
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If the <b>schema=</b> options is omitted, then the first line of the CSV
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file determines the names of the columns.
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</p></li></ul>
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<h1 id="column_names"><span>3. </span>Column Names</h1>
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<p>
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The column names of the virtual table are determined primarily by the
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<b>schema=</b> argument.
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If the <b>schema=</b> argument is omitted, but <b>header</b> is true, then
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the values found in the first line of the CSV file become the column names.
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If the <b>schema=</b> argument is omitted and <b>header</b> is false, then
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the columns are named "c0", "c1", "c2", and so forth.
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</p>
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