oracle sql 优化（待更新）

1：>=代替>
2:少用*
3:尽量不用having
4:含有子查询的语句中减少对表的查询
SELECT TAB_NAME FROM TABLES WHERE (TAB_NAME,DB_VER) = ( SELECT
TAB_NAME,DB_VER FROM TAB_COLUMNS WHERE VERSION = 604)
5：多使用oracle函数解决问题
6：使用别名 Alias
7:exists替代in、not exists替代 not in
SELECT count(*) FROM xljy_room WHERE CLASSROOM_TYPE_ID> 0 AND CLASSROOM_TYPE_ID IN (SELECT CLASSROOM_TYPE_ID FROM oa2_classroom_type WHERE name ='三人房')
SELECT count(*) FROM xljy_room WHERE CLASSROOM_TYPE_ID> 0 AND EXISTS (SELECT 'X' FROM oa2_classroom_type WHERE name ='三人房' and xljy_room.CLASSROOM_TYPE_ID=CLASSROOM_TYPE_ID)
8:oracle SQL语句会转化为大写再执行？

9：decode,sign函数

select decode(sign(PRICE - 150),0,PRICE*1.1,-30,PRICE*1.2,1,price*1.5),price,sign(PRICE - 150) from xljy_room