Question

I’m trying to build a query to grab all rows from Table 1, then check if a corresponding row exists in Table 2, and if so, pull some data, JOIN and insert into Table 3. This will make more sense in pseudocode – so here’s what I’m trying to do, procedurally, I’m just not sure how to implement this in PL/SQL.

For all rows in T1:
    For all rows in T2:
        if (T1.mycolumn - T2.othercolumn) > 0:
            INSERT INTO T3 (foo, bar) VALUES T1.foo, T2.bar

Thanks!

Answer 1

It sounds like you are describing something like

INSERT INTO t3( foo, bar )
  SELECT t1.foo,
         t2.bar
    FROM t1
         LEFT OUTER JOIN t2 ON (t1.mycolumn > t2.othercolumn)

I’m not sure that’s actually what you want, though. Some sample data and the expected output would be helpful. In what you’re describing, t1.foo values may get inserted many times into t3 because they match many different rows in t2. Normally, there would be some sort of key that is common to t1 and t2 that you would use to determine whether an appropriate t2 row exists and the t1.mycolumn > t2.otherColumn condition would just be another predicate

INSERT INTO t3( foo, bar )
  SELECT t1.foo,
         t2.bar
    FROM t1
         LEFT OUTER JOIN t2 ON (    t1.someKey = t2.someKey 
                                AND t1.mycolumn > t2.othercolumn)