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Daniel Moura
Asked: 2010-10-19 10:53:35 +0800 CST

Cancel query in MySql

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I have a query running for some hours, if I cancel this query what is going to happen to the database?

The query is an ALTER TABLE that adds a new column.

UPDATE: I executed the script this way

mysql -u username -p database

mysql> ALTER TABLE `table_name` ADD COLUMN `new_column` INT(1);
mysql database query

2 Answers

  1. AFAIK you could run:

    SHOW PROCESSLIST;

    To see what thread it is then kill it:

    KILL [CONNECTION | QUERY] thread_id;

    During ALTER TABLE, the kill flag is checked before each block of rows are read from the original table. If the kill flag was set, the statement is aborted and the temporary table is deleted.

    About the side effects i won't be able to tell your exactly what could happen.

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  2. I could be wrong here, but if you don't specify a BEGIN TRANSACTION, each and every command is a self-contained transaction.

    As such, when you cancel the query there shouldn't be any side effects.

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