Oracle 颠覆认知的无函数处理限定条件字段也可以用上函数索引(2)
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Oracle 颠覆认知的无函数处理限定条件字段也可以用上函数索引(2)
以前遇到过一次:Oracle 颠覆认知的无函数处理限定条件字段也可以用上函数索引
现在遇到了新的情况:nvl函数处理的可以用上普通索引。
SQL语句如下:
SELECT A.*, A."ROWID" FROM X_XXXXXXXXX_LOG A WHERE 1 = 1 AND NVL(A.IS_XXXX, '0') = '0' AND ROWNUM <= 40 AND A.XXXXXX_TIME > SYSDATE - 30;
表X_XXXXXXXXX_LOG的索引情况:
INDEX_NAME UNIQUENESS COLUMN_NAMES STATUS ------------------------------ ---------- -------------------------------------------------- ------------------------ PK_X_XXXXXXXXX_LOG UNIQUE XXX_NO VALID IDX_TOL_IS_XXXX NONUNIQUE IS_XXXX VALID
SQL执行情况:
可以用上普通索引。
14:25:47 SYS@xxxxxxx(1438)> SELECT A.*, A."ROWID" 14:26:02 2 FROM X_XXXXXXXXX_LOG A 14:26:02 3 WHERE 1 = 1 14:26:02 4 AND NVL(A.IS_XXXX, '0') = '0' 14:26:02 5 AND ROWNUM <= 40 14:26:02 6 AND A.XXXXXX_TIME > SYSDATE - 30; no rows selected Elapsed: 00:00:00.01 14:26:03 SYS@xxxxxxx(1438)> select * from table(dbms_xplan.display_cursor(null,null,'allstats last')); PLAN_TABLE_OUTPUT ---------------------------------------------------------------------------------------------------------- SQL_ID ghh7gfcjtvx41, child number 0 ------------------------------------- SELECT A.*, A."ROWID" FROM X_XXXXXXXXX_LOG A WHERE 1 = 1 AND NVL(A.IS_XXXX, '0') = '0' AND ROWNUM <= 40 AND A.XXXXXX_TIME > SYSDATE - 30 Plan hash value: 3775263249 ---------------------------------------------------------------------------------------------------------- | Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | ---------------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | | 0 |00:00:00.01 | 3 | |* 1 | COUNT STOPKEY | | 1 | | 0 |00:00:00.01 | 3 | |* 2 | TABLE ACCESS BY INDEX ROWID| X_XXXXXXXXX_LOG | 1 | 1 | 0 |00:00:00.01 | 3 | |* 3 | INDEX RANGE SCAN | IDX_TOL_IS_XXXX | 1 | 1 | 0 |00:00:00.01 | 3 | ---------------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter(ROWNUM<=40) 2 - filter("A"."XXXXXX_TIME">SYSDATE@!-30) 3 - access("A"."IS_XXXX"='0')
仔细看执行计划发现谓词条件里边并没有IS_XXXX IS NULL的过滤。
于是,DESC发现表的该字段为not null限制:
14:29:21 SYS@xxxxxxx(1438)> set line 80 14:29:25 SYS@xxxxxxx(1438)> desc X_XXXXXXXXX_LOG Name Null? Type ----------------------------------------- -------- ---------------------------- XXX_NO NOT NULL VARCHAR2(36) XXXX_CODE VARCHAR2(20) XXXXX_NO VARCHAR2(32) XXXX_NO VARCHAR2(60) XXXX_TYPE VARCHAR2(2) XXXX_ID VARCHAR2(20) XXXX_TIME DATE REXXXX VARCHAR2(1500) IS_XXXX NOT NULL VARCHAR2(1) XXXX_TIME DATE XXXXXX_TIME NOT NULL DATE
实际上CBO把NVL(A.IS_XXXX, '0') = '0'等价为了IS_XXXX='0'了,所以用了索引。
大呼一声:Oracle牛逼。
标签:00,XXXX,函数,LOG,XXXXXXXXX,字段,VARCHAR2,Oracle,14 来源: https://www.cnblogs.com/PiscesCanon/p/15879282.html