208 lines
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HTML
208 lines
7.0 KiB
HTML
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<div class="fancy_title">
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The Bytecode() And Tables_Used() Table-Valued Functions
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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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Bytecode and tables_used are <a href="vtab.html">virtual tables</a> built into SQLite that
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access information about <a href="c3ref/stmt.html">prepared statements</a>.
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Both bytecode and tables_used operate as <a href="vtab.html#tabfunc2">table-valued functions</a>.
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They take a single required argument which is either the text of
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an SQL statement, or a pointer to an existing prepared statement.
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The bytecode function returns one row of result for each <a href="opcode.html">bytecode</a>
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operation in the prepared statement. The tables_used function returns
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one row for each persistent btree (either a table or an index) accessed
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by the prepared statement.
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</p><h1 id="usage"><span>2. </span>Usage</h1>
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<p>
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The bytecode and tables_used tables are only available if SQLite has
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been compiled with the <a href="compile.html#enable_bytecode_vtab">-DSQLITE_ENABLE_BYTECODE_VTAB</a> compile-time option.
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The <a href="cli.html">CLI</a> has been compiled that way, and so you can use the standard
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<a href="cli.html">CLI</a> as a test platform to experiement.
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</p><p>
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Both virtual tables are read-only <a href="vtab.html#epoonlyvtab">eponymous-only virtual tables</a>. You use them
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by mentioning them directly in the FROM clause of a SELECT statement.
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They both require a single argument which is the SQL statement to be
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analyzed. For example:
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</p><div class="codeblock"><pre>SELECT * FROM bytecode('SELECT * FROM bytecode(?1)');
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</pre></div>
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<p>
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The argument can be either the text of an SQL statement, in which case
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the bytecode (or tables_used) for that statement is returned, or the
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argument can be a parameter such as ?1 or $stmt that is later bound
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to a <a href="c3ref/stmt.html">prepared statement</a> object using the
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<a href="c3ref/bind_blob.html">sqlite3_bind_pointer()</a> interface. Use a pointer type of
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"stmt-pointer" for the <a href="c3ref/bind_blob.html">sqlite3_bind_pointer()</a> interface.
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</p><h2 id="schema"><span>2.1. </span>Schema</h2>
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<p>
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The schema of the bytecode table is:
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</p><div class="codeblock"><pre>CREATE TABLE bytecode(
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addr INT,
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opcode TEXT,
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p1 INT,
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p2 INT,
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p3 INT,
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p4 TEXT,
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p5 INT,
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comment TEXT,
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subprog TEXT,
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stmt HIDDEN
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);
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</pre></div>
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<p>
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The first eight columns are the address, opcode, and operands for a
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single <a href="opcode.html">bytecode</a> in the virtual machine that implements the statement.
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These columns are the same columns output when using EXPLAIN. The
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bytecode virtual tables shows all operations in the prepared statement,
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both the main body of the prepared statement and in subprograms used
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to implement triggers or foreign key actions. The "subprog" field
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is NULL for the main body of the prepared statement, or is the trigger
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name or the string "(FK)" for triggers and foreign key actions.
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</p><p>
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The schema for the tables_used table is:
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</p><div class="codeblock"><pre>CREATE TABLE tables_used(
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type TEXT,
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schema TEXT,
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name TEXT,
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wr INT,
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subprog TEXT,
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stmt HIDDEN
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);
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</pre></div>
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<p>
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The tables_used table is intended to show which btrees of the database file
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are read or written by a prepared statement, both by the main statement
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itself but also by related triggers and foreign key actions. The columns
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are as follows:
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</p><ul>
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<li><p><b>type</b> → Either "table" or "index", depending on what role
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the btree is serving.
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</p></li><li><p><b>schema</b> → Which database file the btree is located in.
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This will be "main" for the main database (the usual case), or "temp" for
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TEMP tables and indexes, or the name assigned to <a href="lang_attach.html">attached</a> databases by
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the <a href="lang_attach.html">ATTACH</a> statement.
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</p></li><li><p><b>name</b> → The name of the table or index
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</p></li><li><p><b>wr</b> → 0 if the object is read, 1 if the object is written
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</p></li><li><p><b>subprog</b> → The sub-program in which the object is
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accessed. NULL means the main body of the prepared statement. Otherwise
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this field is the name of a trigger or "(FK)" for a foreign key action.
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</p></li></ul>
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