Tips For SQL Query Tunning

Use below tips to increase sql query performance.
1. The sql query becomes faster if you use the actual columns names in SELECT statement instead of than '*'.
EX: select * from table;
    select col1,col2,.... from table;  -- faster when compared to previous once
   
2. Try to avoid  HAVING clause to filter the records..
3. EXISTS is efficient when most of the filter criteria is in the main query.
4. IN is efficient when most of the filter criteria is in the sub-query.
5. Separate all words with a single space.
6. Use any harcoded values in last of the where clause. Because sql engine execute the statements from last.
EX: select a.*  from emp a, dept b
      where a.deptno = b.deptono
      and b.deptno = 40;