Database query optimization method

1.SELECT Try to avoid the use of  *
2. Delete duplicate records
3. Delete all tables （ Retention structure ） Time use TRUNCATE Instead of DELETE
4. use WHERE Instead of HAVING
5. use EXISTS Instead of IN、 use NOT EXISTS Instead of NOT IN
6. Using indexes to improve efficiency , But not more is better , The index number of a table should not exceed 6 individual
7. Try to use numeric fields
8. Try to avoid full scan , You can first consider WHERE And ORDER BY Index the columns involved

Supplement and sort out ing