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    <ol> <li><code>t1</code> will be not be <a href="http://dev.mysql.com/doc/refman/5.0/en/lock-tables-and-triggers.html" rel="nofollow">locked implicitly</a>, as the docs for implicit locking explain would be the case if you were doing the reverse (locking <code>t1</code> will lock <code>t2</code></li> <li>A MySQL Error (ERROR 1100 (HY000): Table <code>t1</code> was not locked with LOCK TABLES) will be generated on attempting to insert into <code>t1</code> because it has not been locked, but the destination of its trigger has.</li> <li>N/A, the query to write to <code>t1</code> is not permitted by the MySQL engine.</li> </ol> <p>Please consider your use case here however. If you are simply copying INSERTS into another table, and not calculating something, you might want to give a thought to using replication instead.</p> <p>Verified on MySQL 5.1 with the following SQL of a toy action log:</p> <pre><code>DROP TABLE IF EXISTS acts, actions; CREATE TABLE acts ( act_id int unsigned not null auto_increment primary key, user_id int unsigned not null ) ENGINE=innodb; CREATE TABLE actions ( action_id int unsigned not null auto_increment primary key, act_id int unsigned not null, user_id int unsigned not null ) ENGINE=innodb; DELIMITER # CREATE TRIGGER acts_post_ins_trigger AFTER INSERT ON acts FOR EACH ROW BEGIN INSERT INTO actions(act_id, user_id) VALUES (new.act_id, new.user_id); END# DELIMITER ; INSERT INTO acts VALUES(1,2); SELECT * FROM acts; SELECT * FROM actions; LOCK TABLE actions WRITE; SELECT('trying to SELECT acts w/ actions locked...') AS 'SELECT TEST'; SELECT * FROM acts; SELECT('trying to INSERT into acts w/ actions locked...') AS 'INSERT TEST'; INSERT INTO acts VALUES(3,4); UNLOCK TABLES; </code></pre>
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    1. POConsequences of locking a table that is acted upon via triggers?
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    1. POConsequences of locking a table that is acted upon via triggers?
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    1. COThanks, Shelhamer. I read the docs about the implicit locks, but I was under the impression that they were talking about triggers _of the locked table_, not triggers _on other tables, which interact with a locked table_. If, as you say, it's whether the source or destination are locked, that's informative. My use case is actually considerably more complex than this (looking to ALTER a table in production using this method), but the notice is well received for the general case.
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    2. COI am speaking from memory on a big MySQL/PHP site here, and have not re-tested this, but I believe it to be correct. If I have time to verify this during lunch I'll let you know.
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    3. CO@umbrae, I have just tested this in a DB and my original answer was in fact correct: a MySQL error will be thrown because the tables involved in the trigger have not all been locked. Implicit locking only occurs when the table that is the *source* of the trigger is locked.
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