Explicitly lock one or more tables. This statement acquires read or write locks on tables, preventing other sessions from accessing them.
The lock_type can be one of:
MariaDB enables client sessions to acquire table locks explicitly for the purpose of cooperating with other sessions for access to tables, or to prevent other sessions from modifying tables during periods when a session requires exclusive access to them. A session can acquire or release locks only for itself. One session cannot acquire locks for another session or release locks held by another session.
Locks may be used to emulate transactions or to get more speed when updating tables.
LOCK TABLES explicitly acquires table locks for the current client session. Table locks can be acquired for base tables or views. To use LOCK TABLES, you must have the LOCK TABLES privilege, and the SELECT privilege for each object to be locked. See .
For view locking, LOCK TABLES adds all base tables used in the view to the set of tables to be locked and locks them automatically. If you lock a table explicitly with LOCK TABLES, any tables used in triggers are also locked implicitly, as described in .
explicitly releases any table locks held by the current session.
Aliases need to correspond to the aliases used in prior SQL statements in the session. For example:
Set the lock wait timeout. See .
LOCK TABLES . You may experience crashes or locks when used with Galera.
LOCK TABLES works on XtraDB/InnoDB tables only if the system variable is set to 1 (the default) and is set to 0 (1 is default). Please note that no error message will be returned on LOCK TABLES with innodb_table_locks = 0.
LOCK TABLES the active transaction, if any. Also, starting a transaction always releases all table locks acquired with LOCK TABLES. This means that there is no way to have table locks and an active transaction at the same time. The only exceptions are the transactions in
While a connection holds an explicit lock on a table, it cannot access a non-locked table. If you try, the following error will be produced:
While a connection holds an explicit lock on a table, it cannot issue the following: INSERT DELAYED, CREATE TABLE, CREATE TABLE ... LIKE, and DDL statements involving stored programs and views (except for triggers). If you try, the following error will be produced:
LOCK TABLES can not be used in stored routines - if you try, the following error will be produced on creation:
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LOCK TABLE[S]
tbl_name [[AS] alias] lock_type
[, tbl_name [[AS] alias] lock_type] ...
[WAIT n|NOWAIT]
lock_type:
READ [LOCAL]
| [LOW_PRIORITY] WRITE
| WRITE CONCURRENT
UNLOCK TABLESWhen using LOCK TABLES on a TEMPORARY table, it will always be locked with a WRITE lock.
While a connection holds an explicit read lock on a table, it cannot modify it. If you try, the following error will be produced:
READ
Read lock, no writes allowed
READ LOCAL
Read lock, but allow concurrent inserts
WRITE
Exclusive write lock. No other connections can read or write to this table
LOW_PRIORITY WRITE
Exclusive write lock, but allow new read locks on the table until we get the write lock.
WRITE CONCURRENT
Exclusive write lock, but allow READ LOCAL locks to the table.
LOCK TABLE t1 AS t1_alias1 READ;
SELECT * FROM t1;
ERROR 1100 (HY000): Table 't1' was not locked with LOCK TABLES
SELECT * FROM t1 AS t1_alias2;
ERROR 1100 (HY000): Table 't1_alias2' was not locked with LOCK TABLES
SELECT * FROM t1 AS t1_alias1;ERROR 1099 (HY000): Table 'tab_name' was locked with a READ lock and can't be updatedERROR 1100 (HY000): Table 'tab_name' was not locked with LOCK TABLESERROR 1192 (HY000): Can't execute the given command because you have active locked tables or an active transactionERROR 1314 (0A000): LOCK is not allowed in stored procedures