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Add an entry to faq.tcl regarding SQLITE_SCHEMA errors. (CVS 2277)

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FossilOrigin-Name: 12defe8cd6a0d7434c8f74b88169155d47299079
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danielk1977
2005-01-26 10:39:58 +00:00
parent e257300f2e
commit f87d01abe9
3 changed files with 60 additions and 8 deletions
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www/faq.tcl
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@@ -1,7 +1,7 @@
#
# Run this script to generated a faq.html output file
#
set rcsid {$Id: faq.tcl,v 1.27 2004/11/10 05:48:57 danielk1977 Exp $}
set rcsid {$Id: faq.tcl,v 1.28 2005/01/26 10:39:58 danielk1977 Exp $}
source common.tcl
header {SQLite Frequently Asked Questions</title>}
@@ -426,6 +426,58 @@ faq {
</pre></blockquote>
}
faq {What is an SQLITE_SCHEMA error, and why am I getting one?} {
<p>In version 3 of SQLite, an SQLITE_SCHEMA error is returned when a
prepared SQL statement is no longer valid and cannot be executed.
When this occurs, the statement must be recompiled from SQL using
the sqlite3_prepare() API. In SQLite 3, an SQLITE_SCHEMA error can
only occur when using the sqlite3_prepare()/sqlite3_step()/sqlite3_finalize()
API to execute SQL, not when using the sqlite3_exec(). This was not
the case in version 2.</p>
<p>The most common reason for a prepared statement to become invalid
is that the schema of the database was modified after the SQL was
prepared (possibly by another process). The other reasons this can
happen are:</p>
<ul>
<li>A database was DETACHed.
<li>A user-function definition was deleted or changed.
<li>A collation sequence definition was deleted or changed.
<li>The authorization function was changed.
</ul>
<p>In all cases, the solution is to recompile the statement from SQL
and attempt to execute it again. Because a prepared statement can be
invalidated by another process changing the database schema, all code
that uses the sqlite3_prepare()/sqlite3_step()/sqlite3_finalize()
API should be prepared to handle SQLITE_SCHEMA errors. An example
of one approach to this follows:</p>
<blockquote><pre>
int rc;
sqlite3_stmt *pStmt;
char zSql[] = "SELECT .....";
do {
/* Compile the statement from SQL. Assume success. */
sqlite3_prepare(pDb, zSql, -1, &pStmt, 0);
while( SQLITE_ROW==sqlite3_step(pStmt) ){
/* Do something with the row of available data */
}
/* Finalize the statement. If an SQLITE_SCHEMA error has
** occured, then the above call to sqlite3_step() will have
** returned SQLITE_ERROR. sqlite3_finalize() will return
** SQLITE_SCHEMA. In this case the loop will execute again.
*/
rc = sqlite3_finalize(pStmt);
} while( rc==SQLITE_SCHEMA );
</pre></blockquote>
}
# End of questions and answers.
#############