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## Session Module C Interface

## Attach A Table To A Session Object

>     int sqlite3session_attach(
>       sqlite3_session *pSession,      /* Session object */
>       const char *zTab                /* Table name */
>     );

If argument zTab is not NULL, then it is the name of a table to attach to the session object passed as the first argument. All subsequent changes made to the table while the session object is enabled will be recorded. See documentation for sqlite3session_changeset() for further details.

Or, if argument zTab is NULL, then changes are recorded for all tables in the database. If additional tables are added to the database (by executing "CREATE TABLE" statements) after this call is made, changes for the new tables are also recorded.

Changes can only be recorded for tables that have a PRIMARY KEY explicitly defined as part of their CREATE TABLE statement. It does not matter if the PRIMARY KEY is an "INTEGER PRIMARY KEY" (rowid alias) or not. The PRIMARY KEY may consist of a single column, or may be a composite key.

It is not an error if the named table does not exist in the database. Nor is it an error if the named table does not have a PRIMARY KEY. However, no changes will be recorded in either of these scenarios.

Changes are not recorded for individual rows that have NULL values stored in one or more of their PRIMARY KEY columns.

SQLITE_OK is returned if the call completes without error. Or, if an error occurs, an SQLite error code (e.g. SQLITE_NOMEM) is returned.

### Special sqlite_stat1 Handling

As of SQLite version 3.22.0, the "sqlite_stat1" table is an exception to some of the rules above. In SQLite, the schema of sqlite_stat1 is:

           CREATE TABLE sqlite_stat1(tbl,idx,stat)

Even though sqlite_stat1 does not have a PRIMARY KEY, changes are recorded for it as if the PRIMARY KEY is (tbl,idx). Additionally, changes are recorded for rows for which (idx IS NULL) is true. However, for such rows a zero-length blob (SQL value X'') is stored in the changeset or patchset instead of a NULL value. This allows such changesets to be manipulated by legacy implementations of sqlite3changeset_invert(), concat() and similar.

The sqlite3changeset_apply() function automatically converts the zero-length blob back to a NULL value when updating the sqlite_stat1 table. However, if the application calls sqlite3changeset_new(), sqlite3changeset_old() or sqlite3changeset_conflict on a changeset iterator directly (including on a changeset iterator passed to a conflict-handler callback) then the X'' value is returned. The application must translate X'' to NULL itself if required.

Legacy (older than 3.22.0) versions of the sessions module cannot capture changes made to the sqlite_stat1 table. Legacy versions of the sqlite3changeset_apply() function silently ignore any modifications to the sqlite_stat1 table that are part of a changeset or patchset.

See also lists of Objects, Constants, and Functions.