Question

I am writing a MySQL query that locks a table:

"LOCK TABLE table_1 WRITE"

After that i am executing some functions, and in one of those functions, I am executing another query, on another table that I haven’t locked:

"SELECT * FROM completely_different_table_2"

Then i get the following error message as result:

Table 'completely_different_table_2' was not locked with LOCKED TABLES 

Indeed, MySql is right to tell me that the table is not locked. But why does it throws an error? Anyone any ideas how I could solve this?

Thanks in advance.

Answer 1

You have to lock every table, that you want to use until the LOCK is released. You can give completely_different_table_2 only a READ LOCK, which allows other processes to read this table while it is locked:

LOCK TABLES table_1 WRITE, completely_different_table_2 READ;

PS: MySQL has a reason to do so. If you request a LOCK, you want to freeze a consistent state of your data. If you read data from completely_different_table_2 inside your LOCK, your data written to table_1 will in some way depend on this other table. Therefore you don’t want anyone to change this table during your LOCK and request a READ LOCK for this second table as well. If your data written to table_1 doesn’t depend on the other table, simply don’t query it until the LOCK is released.