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+<!-- keywords: sqlite3_stmt_readonly -->
+<div class=nosearch>
+<a href="../c3ref/intro.html"><h2>SQLite C Interface</h2></a>
+<h2>Determine If An SQL Statement Writes The Database</h2>
+</div>
+<blockquote><pre>
+int sqlite3_stmt_readonly(sqlite3_stmt *pStmt);
+</pre></blockquote>
+<p>
+The sqlite3_stmt_readonly(X) interface returns true (non-zero) if
+and only if the <a href="../c3ref/stmt.html">prepared statement</a> X makes no direct changes to
+the content of the database file.</p>
+
+<p>Note that <a href="../appfunc.html">application-defined SQL functions</a> or
+<a href="../vtab.html">virtual tables</a> might change the database indirectly as a side effect.
+For example, if an application defines a function "eval()" that
+calls <a href="../c3ref/exec.html">sqlite3_exec()</a>, then the following SQL statement would
+change the database file through side-effects:</p>
+
+<p><blockquote><pre>
+SELECT eval('DELETE FROM t1') FROM t2;
+</pre></blockquote></p>
+
+<p>But because the <a href="../lang_select.html">SELECT</a> statement does not change the database file
+directly, sqlite3_stmt_readonly() would still return true.</p>
+
+<p>Transaction control statements such as <a href="../lang_transaction.html">BEGIN</a>, <a href="../lang_transaction.html">COMMIT</a>, <a href="../lang_transaction.html">ROLLBACK</a>,
+<a href="../lang_savepoint.html">SAVEPOINT</a>, and <a href="../lang_savepoint.html">RELEASE</a> cause sqlite3_stmt_readonly() to return true,
+since the statements themselves do not actually modify the database but
+rather they control the timing of when other statements modify the
+database.  The <a href="../lang_attach.html">ATTACH</a> and <a href="../lang_detach.html">DETACH</a> statements also cause
+sqlite3_stmt_readonly() to return true since, while those statements
+change the configuration of a database connection, they do not make
+changes to the content of the database files on disk.
+The sqlite3_stmt_readonly() interface returns true for <a href="../lang_transaction.html">BEGIN</a> since
+<a href="../lang_transaction.html">BEGIN</a> merely sets internal flags, but the <a href="../lang_transaction.html">BEGIN IMMEDIATE</a> and
+<a href="../lang_transaction.html">BEGIN EXCLUSIVE</a> commands do touch the database and so
+sqlite3_stmt_readonly() returns false for those commands.</p>
+
+<p>This routine returns false if there is any possibility that the
+statement might change the database file.  A false return does
+not guarantee that the statement will change the database file.
+For example, an UPDATE statement might have a WHERE clause that
+makes it a no-op, but the sqlite3_stmt_readonly() result would still
+be false.  Similarly, a CREATE TABLE IF NOT EXISTS statement is a
+read-only no-op if the table already exists, but
+sqlite3_stmt_readonly() still returns false for such a statement.</p>
+
+<p>If prepared statement X is an <a href="../lang_explain.html">EXPLAIN</a> or <a href="../eqp.html">EXPLAIN QUERY PLAN</a>
+statement, then sqlite3_stmt_readonly(X) returns the same value as
+if the EXPLAIN or EXPLAIN QUERY PLAN prefix were omitted.
+</p><p>See also lists of
+  <a href="../c3ref/objlist.html">Objects</a>,
+  <a href="../c3ref/constlist.html">Constants</a>, and
+  <a href="../c3ref/funclist.html">Functions</a>.</p>
+