| Most functions can be combined in a SQL statement. SQL would be far too limited if function combinations were not allowed. The following examples show how some functions can be combined with one another in a query: SELECT LAST_NAME ', ' FIRST_NAME NAME, SUBSTR(EMP_ID,1,3) '-' SUBSTR(EMP_ID,4,2) '-' SUBSTR(EMP_ID,6,4) ID FROM EMPLOYEE_TBL; NAME ID ------------------ ----------- STEPHENS, TINA 311-54-9902 PLEW, LINDA 442-34-6889 GLASS, BRANDON 213-76-4555 GLASS, JACOB 313-78-2439 WALLACE, MARIAH 220-98-4332 SPURGEON, TIFFANY 443-67-9012 6 rows selected. The following example combines two functions in the query (concatenation with substring). By pulling the EMP_ID column apart into three pieces, you can concatenate those pieces with dashes to render a readable Social Security number. SELECT SUM(LENGTH(LAST_NAME) + LENGTH(FIRST_NAME)) TOTAL FROM EMPLOYEE_TBL; TOTAL ---------- 71 1 row selected. This example uses the LENGTH function and the arithmetic operator (+) to add the length of the first name to the length of the last name for each column; the SUM function then finds the total length of all first and last names . | | When embedding functions within functions in a SQL statement, remember that the innermost function is resolved first, and then each function is subsequently resolved from the inside out. | |