How can I do an UPDATE statement with JOIN in SQL Server?

Question

I need to update this table in SQL Server with data from its 'parent' table, see below:

Table: sale

id (int) udid (int) assid (int) 

Table: ud

id  (int) assid  (int) 

sale.assid contains the correct value to update ud.assid.

What query will do this? I'm thinking of a join but I'm not sure if it's possible.

Answer 1

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 

PostgreSQL:

update ud   set assid = s.assid from sale s  where ud.id = s.udid; 

Note that the target table must not be repeated in the FROM clause for Postgres.

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 

SQLite:

update ud       set assid = (           select sale.assid            from sale            where sale.udid = ud.id      )  where RowID in (       select RowID        from ud        where sale.udid = ud.id  );