243 lines
11 KiB
HTML
243 lines
11 KiB
HTML
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<title>Compiling An SQL Statement</title>
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<!-- keywords: {SQL statement compiler} sqlite3_prepare sqlite3_prepare16 sqlite3_prepare16_v2 sqlite3_prepare16_v3 sqlite3_prepare_v2 sqlite3_prepare_v3 -->
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<div class=nosearch>
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<a href="intro.html"><h2>SQLite C Interface</h2></a>
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<h2>Compiling An SQL Statement</h2>
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</div>
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<blockquote><pre>
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int sqlite3_prepare(
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sqlite3 *db, /* Database handle */
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const char *zSql, /* SQL statement, UTF-8 encoded */
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int nByte, /* Maximum length of zSql in bytes. */
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sqlite3_stmt **ppStmt, /* OUT: Statement handle */
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const char **pzTail /* OUT: Pointer to unused portion of zSql */
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);
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int sqlite3_prepare_v2(
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sqlite3 *db, /* Database handle */
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const char *zSql, /* SQL statement, UTF-8 encoded */
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int nByte, /* Maximum length of zSql in bytes. */
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sqlite3_stmt **ppStmt, /* OUT: Statement handle */
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const char **pzTail /* OUT: Pointer to unused portion of zSql */
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);
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int sqlite3_prepare_v3(
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sqlite3 *db, /* Database handle */
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const char *zSql, /* SQL statement, UTF-8 encoded */
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int nByte, /* Maximum length of zSql in bytes. */
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unsigned int prepFlags, /* Zero or more SQLITE_PREPARE_ flags */
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sqlite3_stmt **ppStmt, /* OUT: Statement handle */
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const char **pzTail /* OUT: Pointer to unused portion of zSql */
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);
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int sqlite3_prepare16(
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sqlite3 *db, /* Database handle */
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const void *zSql, /* SQL statement, UTF-16 encoded */
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int nByte, /* Maximum length of zSql in bytes. */
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sqlite3_stmt **ppStmt, /* OUT: Statement handle */
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const void **pzTail /* OUT: Pointer to unused portion of zSql */
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);
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int sqlite3_prepare16_v2(
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sqlite3 *db, /* Database handle */
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const void *zSql, /* SQL statement, UTF-16 encoded */
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int nByte, /* Maximum length of zSql in bytes. */
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sqlite3_stmt **ppStmt, /* OUT: Statement handle */
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const void **pzTail /* OUT: Pointer to unused portion of zSql */
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);
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int sqlite3_prepare16_v3(
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sqlite3 *db, /* Database handle */
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const void *zSql, /* SQL statement, UTF-16 encoded */
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int nByte, /* Maximum length of zSql in bytes. */
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unsigned int prepFlags, /* Zero or more SQLITE_PREPARE_ flags */
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sqlite3_stmt **ppStmt, /* OUT: Statement handle */
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const void **pzTail /* OUT: Pointer to unused portion of zSql */
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);
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</pre></blockquote>
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<p>
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To execute an SQL statement, it must first be compiled into a byte-code
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program using one of these routines. Or, in other words, these routines
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are constructors for the <a href="../c3ref/stmt.html">prepared statement</a> object.</p>
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<p>The preferred routine to use is <a href="../c3ref/prepare.html">sqlite3_prepare_v2()</a>. The
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<a href="../c3ref/prepare.html">sqlite3_prepare()</a> interface is legacy and should be avoided.
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<a href="../c3ref/prepare.html">sqlite3_prepare_v3()</a> has an extra "prepFlags" option that is used
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for special purposes.</p>
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<p>The use of the UTF-8 interfaces is preferred, as SQLite currently
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does all parsing using UTF-8. The UTF-16 interfaces are provided
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as a convenience. The UTF-16 interfaces work by converting the
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input text into UTF-8, then invoking the corresponding UTF-8 interface.</p>
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<p>The first argument, "db", is a <a href="../c3ref/sqlite3.html">database connection</a> obtained from a
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prior successful call to <a href="../c3ref/open.html">sqlite3_open()</a>, <a href="../c3ref/open.html">sqlite3_open_v2()</a> or
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<a href="../c3ref/open.html">sqlite3_open16()</a>. The database connection must not have been closed.</p>
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<p>The second argument, "zSql", is the statement to be compiled, encoded
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as either UTF-8 or UTF-16. The sqlite3_prepare(), sqlite3_prepare_v2(),
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and sqlite3_prepare_v3()
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interfaces use UTF-8, and sqlite3_prepare16(), sqlite3_prepare16_v2(),
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and sqlite3_prepare16_v3() use UTF-16.</p>
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<p>If the nByte argument is negative, then zSql is read up to the
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first zero terminator. If nByte is positive, then it is the
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number of bytes read from zSql. If nByte is zero, then no prepared
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statement is generated.
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If the caller knows that the supplied string is nul-terminated, then
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there is a small performance advantage to passing an nByte parameter that
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is the number of bytes in the input string <i>including</i>
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the nul-terminator.</p>
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<p>If pzTail is not NULL then *pzTail is made to point to the first byte
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past the end of the first SQL statement in zSql. These routines only
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compile the first statement in zSql, so *pzTail is left pointing to
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what remains uncompiled.</p>
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<p>*ppStmt is left pointing to a compiled <a href="../c3ref/stmt.html">prepared statement</a> that can be
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executed using <a href="../c3ref/step.html">sqlite3_step()</a>. If there is an error, *ppStmt is set
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to NULL. If the input text contains no SQL (if the input is an empty
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string or a comment) then *ppStmt is set to NULL.
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The calling procedure is responsible for deleting the compiled
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SQL statement using <a href="../c3ref/finalize.html">sqlite3_finalize()</a> after it has finished with it.
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ppStmt may not be NULL.</p>
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<p>On success, the sqlite3_prepare() family of routines return <a href="../rescode.html#ok">SQLITE_OK</a>;
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otherwise an <a href="../rescode.html">error code</a> is returned.</p>
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<p>The sqlite3_prepare_v2(), sqlite3_prepare_v3(), sqlite3_prepare16_v2(),
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and sqlite3_prepare16_v3() interfaces are recommended for all new programs.
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The older interfaces (sqlite3_prepare() and sqlite3_prepare16())
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are retained for backwards compatibility, but their use is discouraged.
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In the "vX" interfaces, the prepared statement
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that is returned (the <a href="../c3ref/stmt.html">sqlite3_stmt</a> object) contains a copy of the
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original SQL text. This causes the <a href="../c3ref/step.html">sqlite3_step()</a> interface to
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behave differently in three ways:</p>
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<p><ol>
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<li>
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If the database schema changes, instead of returning <a href="../rescode.html#schema">SQLITE_SCHEMA</a> as it
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always used to do, <a href="../c3ref/step.html">sqlite3_step()</a> will automatically recompile the SQL
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statement and try to run it again. As many as <a href="../compile.html#max_schema_retry">SQLITE_MAX_SCHEMA_RETRY</a>
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retries will occur before sqlite3_step() gives up and returns an error.
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</li></p>
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<p><li>
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When an error occurs, <a href="../c3ref/step.html">sqlite3_step()</a> will return one of the detailed
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<a href="../rescode.html">error codes</a> or <a href="../rescode.html#extrc">extended error codes</a>. The legacy behavior was that
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<a href="../c3ref/step.html">sqlite3_step()</a> would only return a generic <a href="../rescode.html#error">SQLITE_ERROR</a> result code
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and the application would have to make a second call to <a href="../c3ref/reset.html">sqlite3_reset()</a>
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in order to find the underlying cause of the problem. With the "v2" prepare
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interfaces, the underlying reason for the error is returned immediately.
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</li></p>
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<p><li>
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If the specific value bound to a <a href="../lang_expr.html#varparam">host parameter</a> in the
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WHERE clause might influence the choice of query plan for a statement,
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then the statement will be automatically recompiled, as if there had been
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a schema change, on the first <a href="../c3ref/step.html">sqlite3_step()</a> call following any change
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to the <a href="../c3ref/bind_blob.html">bindings</a> of that <a href="../lang_expr.html#varparam">parameter</a>.
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The specific value of a WHERE-clause <a href="../lang_expr.html#varparam">parameter</a> might influence the
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choice of query plan if the parameter is the left-hand side of a <a href="../lang_expr.html#like">LIKE</a>
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or <a href="../lang_expr.html#glob">GLOB</a> operator or if the parameter is compared to an indexed column
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and the <a href="../compile.html#enable_stat4">SQLITE_ENABLE_STAT4</a> compile-time option is enabled.
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</li>
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</ol></p>
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<p><p>sqlite3_prepare_v3() differs from sqlite3_prepare_v2() only in having
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the extra prepFlags parameter, which is a bit array consisting of zero or
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more of the <a href="../c3ref/c_prepare_normalize.html#sqlitepreparepersistent">SQLITE_PREPARE_*</a> flags. The
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sqlite3_prepare_v2() interface works exactly the same as
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sqlite3_prepare_v3() with a zero prepFlags parameter.
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</p><p>See also lists of
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<a href="objlist.html">Objects</a>,
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<a href="constlist.html">Constants</a>, and
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<a href="funclist.html">Functions</a>.</p>
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