Question

This should be a simple problem but I can’t seem to find an exact solution. This is basically what I have:

table_1:

id*   scenario*    val1     val2
---   --------     -----    ------
AC1    1            2        0
AC2    1            1        0 
AC1    2            4        0
AC2    2            3        0

table_2:

id*     val3
---     ------
AC1       4
AC2       6

All I want to do is update val2 of table_1 where scenario = 1 with values from table_2 with matching id but I want it to equal val1 + val3 (I don’t know how to make this less obfuscated). So for this example I want table_1 to become:

id*   scenario*    val1     val2
---   --------     ------   --------
AC1    1            2        6
AC2    1            1        7 
AC1    2            4        0
AC2    2            3        0

I think this can be done with a simple MySQL statement but I don’t know how to structure it with a condition for the first table (“INSERT INTO table_1 WHERE scenario=1 SELECT…”??) and the arithmetic of two columns from two different tables.

Answer 1

Try this:

UPDATE table_1 
SET val2 = val1 + 
    (SELECT val3 FROM table_2
     WHERE id = table_1.id
     LIMIT 0,1)
WHERE scenario = 1