Sams Teach Yourself SQL in 21 Days, Fourth Edition

Make Your SQL Statements Readable

Even though readability doesn't affect the actual performance of SQL statements, good programming practice calls for readable code. Readability is especially important if you have multiple conditions in the WHERE clause. Anyone reading the clause should be able to determine whether the tables are being joined properly and should be able to understand the order of the conditions.

Try to read this statement:

SQL> SELECT EMPLOYEE_TBL.EMPLOYEE_ID, EMPLOYEE_TBL.NAME,
						EMPLOYEE_PAY_TBL.SALARY,EMPLOYEE_PAY_TBL.HIRE_DATE
  2  FROM EMPLOYEE_TBL, EMPLOYEE_PAY_TBL
  3  WHERE EMPLOYEE_TBL.EMPLOYEE_ID = EMPLOYEE_PAY_TBL.EMPLOYEE_ID AND
  4  EMPLOYEE_PAY_TBL.SALARY > 30000 OR (EMPLOYEE_PAY_TBL.SALARY BETWEEN 25000
  5  AND 30000 AND EMPLOYEE_PAY_TBL.HIRE_DATE ...