SQL’where’子句中的条件的执行顺序

我在我的where子句中有一组条件

WHERE 
d.attribute3 = 'abcd*'  
AND x.STATUS != 'P' 
AND x.STATUS != 'J' 
AND x.STATUS != 'X' 
AND x.STATUS != 'S' 
AND x.STATUS != 'D' 
AND CURRENT_TIMESTAMP - 1 < x.CREATION_TIMESTAMP

首先执行以下哪些条件？我正在使用oracle.

我在执行计划中会得到这些细节吗？
(我没有权限在db中这样做,否则我会尝试)

解决方法

你确定你没有权限去看执行计划吗？如何使用AUTOTRACE？

sql> set autotrace on
sql> select * from emp
  2  join dept on dept.deptno = emp.deptno
  3  where emp.ename like 'K%'
  4  and dept.loc like 'l%'
  5  /

no rows selected


Execution Plan
----------------------------------------------------------

----------------------------------------------------------------------------------
| Id  | Operation                    | Name         | Rows  | Bytes | Cost (%cpu)|
----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |              |     1 |    62 |     4   (0)|
|   1 |  nesTED LOOPS                |              |     1 |    62 |     4   (0)|
|*  2 |   TABLE ACCESS FULL          | EMP          |     1 |    42 |     3   (0)|
|*  3 |   TABLE ACCESS BY INDEX ROWID| DEPT         |     1 |    20 |     1   (0)|
|*  4 |    INDEX UNIQUE SCAN         | SYS_C0042912 |     1 |       |     0   (0)|
----------------------------------------------------------------------------------

Predicate information (identified by operation id):
---------------------------------------------------

   2 - filter("EMP"."ENAME" LIKE 'K%' AND "EMP"."DEPTNO" IS NOT NULL)
   3 - filter("DEPT"."LOC" LIKE 'l%')
   4 - access("DEPT"."DEPTNO"="EMP"."DEPTNO")

可以看到,这给出了关于如何执行查询的很多细节.它告诉我：

>将在EMP的全面扫描上首先应用条件“emp.ename like”K％“”
>那么匹配的DEPT记录将通过dept.deptno上的索引(通过nesTED LOOPS方法)来选择,
>最后将过滤“dept.loc like”l％“将被应用.

这个应用顺序与在WHERE子句中排除谓词的方式无关,我们可以用这个重新排序的查询来显示：

sql> select * from emp
  2  join dept on dept.deptno = emp.deptno
  3  where dept.loc like 'l%'
  4  and emp.ename like 'K%';

no rows selected


Execution Plan
----------------------------------------------------------

----------------------------------------------------------------------------------
| Id  | Operation                    | Name         | Rows  | Bytes | Cost (%cpu)|
----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |              |     1 |    62 |     4   (0)|
|   1 |  nesTED LOOPS                |              |     1 |    62 |     4   (0)|
|*  2 |   TABLE ACCESS FULL          | EMP          |     1 |    42 |     3   (0)|
|*  3 |   TABLE ACCESS BY INDEX ROWID| DEPT         |     1 |    20 |     1   (0)|
|*  4 |    INDEX UNIQUE SCAN         | SYS_C0042912 |     1 |       |     0   (0)|
----------------------------------------------------------------------------------

Predicate information (identified by operation id):
---------------------------------------------------

   2 - filter("EMP"."ENAME" LIKE 'K%' AND "EMP"."DEPTNO" IS NOT NULL)
   3 - filter("DEPT"."LOC" LIKE 'l%')
   4 - access("DEPT"."DEPTNO"="EMP"."DEPTNO")

原文地址：https://www.jb51.cc/mssql/81563.html