Aggregate function in an SQL update query?

user_27290 0
Viewed 111309

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.field2)
FROM table1
INNER JOIN table2 ON table1.field3 = table2.field3
GROUP BY table1.field3

Of course, as this stands, it won't work - SET doesn't support SUM and it doesn't support GROUP BY.

I should know this, but my mind's drawing a blank. What am I doing wrong?

tsql sql-server sql
6 Answers
UPDATE t1
SET t1.field1 = t2.field2Sum
FROM table1 t1
INNER JOIN (select field3, sum(field2) as field2Sum
   from table2
  group by field3) as t2
on t2.field3 = t1.field3
user_1360590

Use:

UPDATE table1
   SET field1 = (SELECT SUM(t2.field2) 
                   FROM TABLE2 t2 
                  WHERE t2.field3 = field2)
user_1351520

Or you could use a mix of JBrooks and OMG Ponies answers:

UPDATE table1
   SET field1 = (SELECT SUM(field2)
                   FROM table2 AS t2
                  WHERE t2.field3 = t1.field3)
  FROM table1 AS t1
Paulo_Santos_443750

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

user_16551550

You can also use CTE like below.

;WITH t2 AS (
    SELECT field3, SUM(field2) AS field2
    FROM table2
    GROUP BY field3
)
UPDATE table1
SET table1.field1 = t2.field2
FROM table1
INNER JOIN t2 ON table1.field3 = t2.field3
user_96952860
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