Update Query Generated By Fetch Query Sql Join Statements

We use JOIN in the SELECT statement often to retrieve data from multiple related tables. Here, we need a sql script which will containUPDATE with JOIN. This tutorial shows you how to perform cross-table update by using MySQL UPDATE JOIN statement with INNER JOIN and LEFT JOIN. We often use join clauses to query rows in a table that have (in the case of INNER JOIN) or may not have (in the case of LEFT JOIN) corresponding rows in another.

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Syntax strictly depends on which SQL DBMS you're using. Here are some ways to do it in ANSI/ISO (aka should work on any SQL DBMS), MySQL, SQL Server, and Oracle. Be advised that my suggested ANSI/ISO method will typically be much slower than the other two methods, but if you're using a SQL DBMS other than MySQL, SQL Server, or Oracle, then it may be the only way to go (e.g. If your SQL DBMS doesn't support MERGE): ANSI/ISO: update ud set assid = ( select sale.assid from sale where sale.udid = ud.id ) where exists ( select * from sale where sale.udid = ud.id ); MySQL: update ud u inner join sale s on u.id = s.udid set u.assid = s.assid SQL Server: update u set u.assid = s.assid from ud u inner join sale s on u.id = s.udid Oracle: update (select u.assid as new_assid, s.assid as old_assid from ud u inner join sale s on u.id = s.udid) up set up.new_assid = up.old_assid. MySQL You'll get the best performance if you forget the where clause and place all conditions in the ON expression.

I think this is because the query first has to join the tables then runs the where clause on that, so if you can reduce what is required to join then that's the fasted way to get the results/do the udpate. Example Scenario You have a table of users. They can log in using their username or email or account_number. These accounts can be active (1) or inactive (0). This table has 50000 rows You then have a table of users to disable at one go because you find out they've all done something bad.

This table however, has one column with usernames, emails and account numbers mixed. It also has a 'has_run' indicator which needs to be set to 1 (true) when it has been run Query UPDATE users User INNER JOIN blacklist_users BlacklistUser ON ( User.username = BlacklistUser.account_ref OR User.email = BlacklistedUser.account_ref OR User.phone_number = BlacklistUser.account_ref AND User.is_active = 1 AND BlacklistUser.has_run = 0 ) SET User.is_active = 0, BlacklistUser.has_run = 1; Reasoning If we had to join on just the OR conditions it would essentially need to check each row 4 times to see if it should join, and potentially return a lot more rows.

However, by giving it more conditions it can 'skip' a lot of rows if they don't meet all the conditions when joining. Bonus It's more readable.

All the conditions are in one place and the rows to update are in one place.