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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_prepare_v2 -->
<div class=nosearch>
<a href="intro.html"><h2>SQLite C Interface</h2></a>
<h2>Compiling An SQL Statement</h2>
</div>
<blockquote><pre>
int sqlite3_prepare(
sqlite3 *db, /* Database handle */
const char *zSql, /* SQL statement, UTF-8 encoded */
int nByte, /* Maximum length of zSql in bytes. */
sqlite3_stmt **ppStmt, /* OUT: Statement handle */
const char **pzTail /* OUT: Pointer to unused portion of zSql */
);
int sqlite3_prepare_v2(
sqlite3 *db, /* Database handle */
const char *zSql, /* SQL statement, UTF-8 encoded */
int nByte, /* Maximum length of zSql in bytes. */
sqlite3_stmt **ppStmt, /* OUT: Statement handle */
const char **pzTail /* OUT: Pointer to unused portion of zSql */
);
int sqlite3_prepare16(
sqlite3 *db, /* Database handle */
const void *zSql, /* SQL statement, UTF-16 encoded */
int nByte, /* Maximum length of zSql in bytes. */
sqlite3_stmt **ppStmt, /* OUT: Statement handle */
const void **pzTail /* OUT: Pointer to unused portion of zSql */
);
int sqlite3_prepare16_v2(
sqlite3 *db, /* Database handle */
const void *zSql, /* SQL statement, UTF-16 encoded */
int nByte, /* Maximum length of zSql in bytes. */
sqlite3_stmt **ppStmt, /* OUT: Statement handle */
const void **pzTail /* OUT: Pointer to unused portion of zSql */
);
</pre></blockquote>
<p>
To execute an SQL query, it must first be compiled into a byte-code
program using one of these routines.</p>
<p>The first argument, "db", is a <a href="../c3ref/sqlite3.html">database connection</a> obtained from a
prior successful call to <a href="../c3ref/open.html">sqlite3_open()</a>, <a href="../c3ref/open.html">sqlite3_open_v2()</a> or
<a href="../c3ref/open.html">sqlite3_open16()</a>. The database connection must not have been closed.</p>
<p>The second argument, "zSql", is the statement to be compiled, encoded
as either UTF-8 or UTF-16. The sqlite3_prepare() and sqlite3_prepare_v2()
interfaces use UTF-8, and sqlite3_prepare16() and sqlite3_prepare16_v2()
use UTF-16.</p>
<p>If the nByte argument is negative, then zSql is read up to the
first zero terminator. If nByte is positive, then it is the
number of bytes read from zSql. If nByte is zero, then no prepared
statement is generated.
If the caller knows that the supplied string is nul-terminated, then
there is a small performance advantage to passing an nByte parameter that
is the number of bytes in the input string <i>including</i>
the nul-terminator.</p>
<p>If pzTail is not NULL then *pzTail is made to point to the first byte
past the end of the first SQL statement in zSql. These routines only
compile the first statement in zSql, so *pzTail is left pointing to
what remains uncompiled.</p>
<p>*ppStmt is left pointing to a compiled <a href="../c3ref/stmt.html">prepared statement</a> that can be
executed using <a href="../c3ref/step.html">sqlite3_step()</a>. If there is an error, *ppStmt is set
to NULL. If the input text contains no SQL (if the input is an empty
string or a comment) then *ppStmt is set to NULL.
The calling procedure is responsible for deleting the compiled
SQL statement using <a href="../c3ref/finalize.html">sqlite3_finalize()</a> after it has finished with it.
ppStmt may not be NULL.</p>
<p>On success, the sqlite3_prepare() family of routines return <a href="../rescode.html#ok">SQLITE_OK</a>;
otherwise an <a href="../rescode.html">error code</a> is returned.</p>
<p>The sqlite3_prepare_v2() and sqlite3_prepare16_v2() interfaces are
recommended for all new programs. The two older interfaces are retained
for backwards compatibility, but their use is discouraged.
In the "v2" interfaces, the prepared statement
that is returned (the <a href="../c3ref/stmt.html">sqlite3_stmt</a> object) contains a copy of the
original SQL text. This causes the <a href="../c3ref/step.html">sqlite3_step()</a> interface to
behave differently in three ways:</p>
<p><ol>
<li>
If the database schema changes, instead of returning <a href="../rescode.html#schema">SQLITE_SCHEMA</a> as it
always used to do, <a href="../c3ref/step.html">sqlite3_step()</a> will automatically recompile the SQL
statement and try to run it again. As many as <a href="../compile.html#max_schema_retry">SQLITE_MAX_SCHEMA_RETRY</a>
retries will occur before sqlite3_step() gives up and returns an error.
</li></p>
<p><li>
When an error occurs, <a href="../c3ref/step.html">sqlite3_step()</a> will return one of the detailed
<a href="../rescode.html">error codes</a> or <a href="../rescode.html#extrc">extended error codes</a>. The legacy behavior was that
<a href="../c3ref/step.html">sqlite3_step()</a> would only return a generic <a href="../rescode.html#error">SQLITE_ERROR</a> result code
and the application would have to make a second call to <a href="../c3ref/reset.html">sqlite3_reset()</a>
in order to find the underlying cause of the problem. With the "v2" prepare
interfaces, the underlying reason for the error is returned immediately.
</li></p>
<p><li>
If the specific value bound to <a href="../lang_expr.html#varparam">host parameter</a> in the
WHERE clause might influence the choice of query plan for a statement,
then the statement will be automatically recompiled, as if there had been
a schema change, on the first <a href="../c3ref/step.html">sqlite3_step()</a> call following any change
to the <a href="../c3ref/bind_blob.html">bindings</a> of that <a href="../lang_expr.html#varparam">parameter</a>.
The specific value of WHERE-clause <a href="../lang_expr.html#varparam">parameter</a> might influence the
choice of query plan if the parameter is the left-hand side of a <a href="../lang_expr.html#like">LIKE</a>
or <a href="../lang_expr.html#glob">GLOB</a> operator or if the parameter is compared to an indexed column
and the <a href="../compile.html#enable_stat3">SQLITE_ENABLE_STAT3</a> compile-time option is enabled.
</li>
</ol>
</p><p>See also lists of
<a href="objlist.html">Objects</a>,
<a href="constlist.html">Constants</a>, and
<a href="funclist.html">Functions</a>.</p>
|
