NO_WAIT and WAIT options. If a DDL statement with WAIT enabled fails to obtain an MDL lock, it will wait for WAIT seconds before it directly returns the query result. If a DDL statement with NO_WAIT enabled, it will directly return the query result without waiting for the MDL lock.NOWAIT and SKIP LOCKED options. If target rows are locked by another transaction, a SELECT FOR UPDATE statement is supposed to wait for the transaction to release the lock. But in some use cases like flash sales, you do not want to wait for a lock. You can use SKIP LOCKED to skip locked rows (as a result, the locked rows won't be returned in the query result set) or NOWAIT to return an error without waiting for the lock.NO_WAIT and NOWAIT are different keywords.SKIP LOCKED or NOWAIT in SELECT FOR UPDATE/SHARE statements. Note that NO_WAIT in DDL statements and NOWAIT in SELECT FOR UPDATE statements are different keywords for historical reasons.피드백