oracle sql 最佳化（待更新）

1：>=代替>
2:少用*
3:盡量不用having
4:含有子查詢的語句中減少對錶的查詢
  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函數解決問題
6：使用別名 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語句會轉化為大寫再執行？

9：decode,sign函數

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