Does select into lock table?

Does select into lock table?

Does select into lock table?

As with a CREATE TABLE statement, if a SELECTINTO statement is contained within an explicit transaction, the underlying row(s) in the affected system tables are exclusively locked until the transaction is explicitly committed.

Why are tables locked in MySQL?

MySQL allows a client session to acquire a table lock explicitly to cooperate with other sessions to access the table's data. MySQL also allows table locking to prevent it from unauthorized modification into the same table during a specific period.

Does MySQL lock table on update?

A locking read, an UPDATE , or a DELETE generally set record locks on every index record that is scanned in the processing of an SQL statement. It does not matter whether there are WHERE conditions in the statement that would exclude the row.

What is the use of lock table query?

The LOCK TABLE statement allows you to explicitly acquire a shared or exclusive table lock on the specified table. The table lock lasts until the end of the current transaction. To lock a table, you must either be the database owner or the table owner.

Is Select into faster than Insert into?

I've had DBAs state, Insert into is faster, since compiler/parser, does not need to find Column data types on the fly. Others stating Select into is faster. We conducted performance testing, and seems select into is slightly faster.

How do I unlock a locked table in MySQL?

The correct way to use LOCK TABLES and UNLOCK TABLES with transactional tables, such as InnoDB tables, is to begin a transaction with SET autocommit = 0 (not START TRANSACTION ) followed by LOCK TABLES , and to not call UNLOCK TABLES until you commit the transaction explicitly.

How do I find a locked table in MySQL?

SHOW OPEN TABLES to show each table status and its lock. SHOW OPEN TABLES WHERE `Table` LIKE '%[TABLE_NAME]%' AND `Database` LIKE '[DBNAME]' AND In_use > 0; to check any locked tables in a database. You can use SHOW OPEN TABLES to show each table's lock status.

Does MySQL lock table on Delete?

Deleting rows from the table will also not block concurrent inserts (as long as there are no primary key conflicts). And inserting rows won't block deleting existing rows.

Can a select query lock the database MySQL?

SELECTs do not normally do any locking that you care about on InnoDB tables. The SELECT will not block, and it will not read any "dirty" un-committed data - but it might skip some rows, e.g. not show all your rows in the table. ...

How do I lock a table in SQL query?

The LOCK TABLE statement allows you to explicitly acquire a shared or exclusive table lock on the specified table. The table lock lasts until the end of the current transaction. To lock a table, you must either be the database owner or the table owner.

How does MySQL management of table locking work?

How MySQL Manages Table Locking. If there are no locks on the table, put a read/write lock on it. Otherwise, put the lock request in the read/write lock queue. When a lock is released, the lock is first made available to other processes in the write lock queue, then to the threads in the read lock queue.

Is there way to select without causing locking in MySQL?

There are other kind of locking issues associated with InnoDB, but you might find it fits your needs. Depending on your table type, locking will perform differently, but so will a SELECT count. For MyISAM tables a simple SELECT count (*) FROM table should not lock the table since it accesses meta data to pull the record count.

What does the lock flag mean in MySQL?

A lock is a flag associated with a table. MySQL allows a client session to explicitly acquire a table lock for preventing other sessions from accessing the same table during a specific period.

Is there a way to select without locking the table?

For MyISAM tables a simple SELECT count (*) FROM table should not lock the table since it accesses meta data to pull the record count. Innodb will take longer since it has to grab the table in a snapshot to count the records, but it shouldn’t cause locking.


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