Cartesian Merge

When trying to ensure a pair of fields match another pair of fields, do not use bars as this creates a Cartesian Merge which can significantly slow down your program. Use commas to separate the fields as shown in the 2nd example.

WRONG CODE:

SELECT field1, field2
FROM table
WHERE field1||field2 IN              /* NO */
  (SELECT field1||fieldS2            /* NO */
     FROM table
    WHERE some conditions);

CORRECT CODE:

SELECT field1, field2
FROM table
WHERE (field1,field2) IN           /* YES */
  (SELECT field1,fieldS2           /* YES */
     FROM table
    WHERE some conditions);