Question

I have a table (TABLE1) which has 4 columns:

UID | PID | VALUE1 | VALUE2

I have another SQL statement (STMT) which returns 3 columns from some other tables:

UID | PID | VALUE1

Now here are the condition of how I want to update TABLE1:

First, compare UID and PID pair from STMT with those in TABLE1,

1. for all new UID and PID pair not in TABLE1, insert new row from STMT into TABLE1, set TABLE1.VALUE2 = 0 (I’ve already done this one)

2. for existing UID and PID pair in both STMT and TABLE1, do:

   a. if TABLE1.VALUE2 > 0, update TABLE1.VALUE1 = STMT.VALUE1

   b. if TABLE1.VALUE2 = 0 and if TABLE1.VALUE1 != STMT.VALUE1, update TABLE1.VALUE1 = STMT.VALUE1, otherwise do nothing.

I’m having trouble coming up with a solution for condition 2. Any help is appreciated!

Answer 1

UPDATE (
    SELECT table1.UID
           ,table1.PID
           ,table1.value1 AS table1_value1
           ,table1.value2 AS table1_value2
           ,stmt.value1 AS stmt_value1
    FROM table1
    INNER JOIN (SELECT ? AS UID
                       ,? AS PID
                       ,? AS value1
                FROM whatever) stmt
        ON stmt.UID = table1.UID
        AND stmt.PID = table1.PID
) x
SET x.table1_VALUE1 = CASE WHEN (x.table1_VALUE2 > 0) OR
                              (x.table1_VALUE2 = 0 AND x.table1_VALUE1 <> x.stmt_VALUE1)
                              THEN x.stmt_VALUE1
                         ELSE x.table1_VALUE1 
                    END