Exclusive lock

Exclusive lock （EXclusive Lock）, also called X lock 、 An exclusive lock 、 Write lock . For row lock .
When a transaction locks the data , Other transactions cannot add any locks to the locked data , Again because InnoDB Yes select Statement is unlocked by default , So other transactions can't be written , It is still allowed to read （ Although read locks are not allowed ）.

It is mainly used for writing transactions , No other transactions are allowed to modify .

Lock mode ：
Automatically ：DML Statement default write lock
Manual ：select * from T where id=1 for update;
Release mode ：
commit、rollback;