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## Session Module C Interface

## Load The Difference Between Tables Into A Session

>     int sqlite3session_diff(
>       sqlite3_session *pSession,
>       const char *zFromDb,
>       const char *zTbl,
>       char **pzErrMsg
>     );

If it is not already attached to the session object passed as the first argument, this function attaches table zTbl in the same manner as the sqlite3session_attach() function. If zTbl does not exist, or if it does not have a primary key, this function is a no-op (but does not return an error).

Argument zFromDb must be the name of a database ("main", "temp" etc.) attached to the same database handle as the session object that contains a table compatible with the table attached to the session by this function. A table is considered compatible if it:

- Has the same name,
- Has the same set of columns declared in the same order, and
- Has the same PRIMARY KEY definition.

If the tables are not compatible, SQLITE_SCHEMA is returned. If the tables are compatible but do not have any PRIMARY KEY columns, it is not an error but no changes are added to the session object. As with other session APIs, tables without PRIMARY KEYs are simply ignored.

This function adds a set of changes to the session object that could be used to update the table in database zFrom (call this the "from-table") so that its content is the same as the table attached to the session object (call this the "to-table"). Specifically:

- For each row (primary key) that exists in the to-table but not in the from-table, an INSERT record is added to the session object.

- For each row (primary key) that exists in the to-table but not in the from-table, a DELETE record is added to the session object.

- For each row (primary key) that exists in both tables, but features different non-PK values in each, an UPDATE record is added to the session.

To clarify, if this function is called and then a changeset constructed using sqlite3session_changeset(), then after applying that changeset to database zFrom the contents of the two compatible tables would be identical.

Unless the call to this function is a no-op as described above, it is an error if database zFrom does not exist or does not contain the required compatible table.

If the operation is successful, SQLITE_OK is returned. Otherwise, an SQLite error code. In this case, if argument pzErrMsg is not NULL, *pzErrMsg may be set to point to a buffer containing an English language error message. It is the responsibility of the caller to free this buffer using sqlite3_free().

See also lists of Objects, Constants, and Functions.