SHOW CREATE TABLE drops index prefix lengths and DESC from primary keys #501

Bug

SHOW CREATE TABLE loses index prefix lengths and descending order in the PRIMARY KEY clause. A table created with PRIMARY KEY (session_id(100)) on a MEDIUMTEXT column is reported as PRIMARY KEY (session_id), and PRIMARY KEY (a DESC, b) comes back as PRIMARY KEY (a, b).

The information schema records the data correctly (SUB_PART = 100, COLLATION = 'D' in _wp_sqlite_mysql_information_schema_statistics); only the PRIMARY KEY branch of the statement reconstruction drops it, while the branch handling all other index types preserves both.

Impact

Any consumer that rebuilds a schema from SHOW CREATE TABLE produces DDL that MySQL rejects: ERROR 1170 (42000): BLOB/TEXT column used in key specification without a key length. This is how the bug surfaces in WordPress Studio's push feature (wp sqlite export relays the statement as is), reported in Automattic/studio#4739.

Reproduction

CREATE TABLE t (session_id MEDIUMTEXT NOT NULL, PRIMARY KEY (session_id(100)));
SHOW CREATE TABLE t;
-- reports: PRIMARY KEY (`session_id`)
-- expected, as in MySQL 8: PRIMARY KEY (`session_id`(100))

Verified against a real MySQL 8 server: its SHOW CREATE TABLE emits PRIMARY KEY (session_id(100)) for the same table, and re-importing the driver's current output fails there with ERROR 1170.