Aggregate function in an SQL update query?

Question

I\'m trying to set the value in one table to the sum of the values in another table. Something along these lines:

UPDATE table1
SET field1 = SUM(table2.fiel         


        

Answer 1

I know the question is tagged SQL Server but be careful with UPDATE with JOIN if you are using PostgreSQL. @JBrooks answer won't work :

UPDATE t1
SET t1.field1 = t2.field2Sum
FROM table1 t1
INNER JOIN (...) as t2
on t2.field3 = t1.field3  

You will have to adapt it to :

UPDATE table1 t1
SET t1.field1 = t2.field2Sum
FROM (...) as t2
WHERE t2.field3 = t1.field3  

See parameter from_list in the doc to get why FROM is considered by PostgreSQL as a self-join : https://www.postgresql.org/docs/9.5/static/sql-update.html#AEN89239