like 与 = 效率上有区别吗？ 在where条件中如果某字段名与变量都是全匹配的话，用like和=有区别吗？ 解决方案 » 免费领取超大流量手机卡，每月29元包185G流量+100分钟通话, 中国电信官方发货 有区别,最主要就是在索引的使用上SQL> select * from test2; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO---------- ---------- --------- ---------- ------------------- ---------- ---------- ---------- 7369 SMITH CLERK 7902 1980-12-17 00:00:00 800 20 7499 ALLEN SALESMAN 7698 1981-02-20 00:00:00 1600 300 30 7521 WARD SALESMAN 7698 1981-02-22 00:00:00 1250 500 30 7566 JONES MANAGER 7839 1981-04-02 00:00:00 2975 20 7654 MARTIN SALESMAN 7698 1981-09-28 00:00:00 1250 1400 30 7698 BLAKE MANAGER 7839 1981-05-01 00:00:00 2850 30 7782 CLARK MANAGER 7839 1981-06-09 00:00:00 2450 10 7788 SCOTT ANALYST 7566 1987-04-19 00:00:00 3000 20 7839 KING PRESIDENT 1981-11-17 00:00:00 5000 10 7844 TURNER SALESMAN 7698 1981-09-08 00:00:00 1500 0 30 7876 ADAMS CLERK 7788 1987-05-23 00:00:00 1100 20 7900 JAMES CLERK 7698 1981-12-03 00:00:00 950 30 7902 FORD ANALYST 7566 1981-12-03 00:00:00 3000 20 7934 MILLER CLERK 7782 1982-01-23 00:00:00 1300 1014 rows selected.Execution Plan----------------------------------------------------------Plan hash value: 300966803---------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |---------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 14 | 1218 | 3 (0)| 00:00:01 || 1 | TABLE ACCESS FULL| TEST2 | 14 | 1218 | 3 (0)| 00:00:01 |---------------------------------------------------------------------------Note----- - dynamic sampling used for this statementStatistics---------------------------------------------------------- 0 recursive calls 0 db block gets 4 consistent gets 0 physical reads 0 redo size 1415 bytes sent via SQL*Net to client 385 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 14 rows processedSQL> select * from test2 2 where ename = 'SMITH'; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO---------- ---------- --------- ---------- ------------------- ---------- ---------- ---------- 7369 SMITH CLERK 7902 1980-12-17 00:00:00 800 20Execution Plan----------------------------------------------------------Plan hash value: 300966803---------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |---------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1 | 87 | 3 (0)| 00:00:01 ||* 1 | TABLE ACCESS FULL| TEST2 | 1 | 87 | 3 (0)| 00:00:01 |---------------------------------------------------------------------------Predicate Information (identified by operation id):--------------------------------------------------- 1 - filter("ENAME"='SMITH')Note----- - dynamic sampling used for this statementStatistics---------------------------------------------------------- 5 recursive calls 0 db block gets 8 consistent gets 0 physical reads 0 redo size 822 bytes sent via SQL*Net to client 385 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processedSQL> create index ind_ename_test2 on test2(ename); Index created.SQL> select * from test2 2 where ename = 'SMITH'; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO---------- ---------- --------- ---------- ------------------- ---------- ---------- ---------- 7369 SMITH CLERK 7902 1980-12-17 00:00:00 800 20Execution Plan----------------------------------------------------------Plan hash value: 923399397-----------------------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |-----------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1 | 87 | 2 (0)| 00:00:01 || 1 | TABLE ACCESS BY INDEX ROWID| TEST2 | 1 | 87 | 2 (0)| 00:00:01 ||* 2 | INDEX RANGE SCAN | IND_ENAME_TEST2 | 1 | | 1 (0)| 00:00:01 |-----------------------------------------------------------------------------------------------Predicate Information (identified by operation id):--------------------------------------------------- 2 - access("ENAME"='SMITH')Note----- - dynamic sampling used for this statementStatistics---------------------------------------------------------- 9 recursive calls 0 db block gets 9 consistent gets 0 physical reads 0 redo size 826 bytes sent via SQL*Net to client 385 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processedSQL> select * from test2 2 where ename like '%SMITH'; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO---------- ---------- --------- ---------- ------------------- ---------- ---------- ---------- 7369 SMITH CLERK 7902 1980-12-17 00:00:00 800 20Execution Plan----------------------------------------------------------Plan hash value: 300966803---------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |---------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1 | 87 | 3 (0)| 00:00:01 ||* 1 | TABLE ACCESS FULL| TEST2 | 1 | 87 | 3 (0)| 00:00:01 |---------------------------------------------------------------------------Predicate Information (identified by operation id):--------------------------------------------------- 1 - filter("ENAME" LIKE '%SMITH')Note----- - dynamic sampling used for this statementStatistics---------------------------------------------------------- 5 recursive calls 0 db block gets 8 consistent gets 0 physical reads 0 redo size 822 bytes sent via SQL*Net to client 385 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed这是一个简单的例子,只是说明区别,实际上索引的使用条件还有很多影响 like的效率要比=低很多，不是一个数量级的。 #3楼用like时加了通配符，这样肯定会破坏索引，从这个例子还是不能看出哪个快啊 下列代码的哪一行有错误？ 两条看似很简单的sql，请高手指教 为什么我使用不了带登陆目录的rman？ SQL*Loader-704: 内部错误: ulconnect: OCIServerAttach [0] 这样的sql server存储过程用oracle怎么写呀！ 如何实现在本地数据库服务器上创建访问其他数据库服务器上的数据视图。。。解决给100分。 oracle blob 字段，我想实现两个数据库之间的复制怎么办？ 在现求救！！！兄弟们帮帮忙！ c3p0 Timeout 超时问题 100分 oralce不同服务器不同表结构数据同步问题 关于SQL跟踪的问题 关于实例无法启动的问题
---------- ---------- --------- ---------- ------------------- ---------- ---------- ----------
7369 SMITH CLERK 7902 1980-12-17 00:00:00 800 20
7499 ALLEN SALESMAN 7698 1981-02-20 00:00:00 1600 300 30
7521 WARD SALESMAN 7698 1981-02-22 00:00:00 1250 500 30
7566 JONES MANAGER 7839 1981-04-02 00:00:00 2975 20
7654 MARTIN SALESMAN 7698 1981-09-28 00:00:00 1250 1400 30
7698 BLAKE MANAGER 7839 1981-05-01 00:00:00 2850 30
7782 CLARK MANAGER 7839 1981-06-09 00:00:00 2450 10
7788 SCOTT ANALYST 7566 1987-04-19 00:00:00 3000 20
7839 KING PRESIDENT 1981-11-17 00:00:00 5000 10
7844 TURNER SALESMAN 7698 1981-09-08 00:00:00 1500 0 30
7876 ADAMS CLERK 7788 1987-05-23 00:00:00 1100 20
7900 JAMES CLERK 7698 1981-12-03 00:00:00 950 30
7902 FORD ANALYST 7566 1981-12-03 00:00:00 3000 20
7934 MILLER CLERK 7782 1982-01-23 00:00:00 1300 1014 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 300966803---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 14 | 1218 | 3 (0)| 00:00:01 |
| 1 | TABLE ACCESS FULL| TEST2 | 14 | 1218 | 3 (0)| 00:00:01 |
---------------------------------------------------------------------------Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
4 consistent gets
0 physical reads
0 redo size
1415 bytes sent via SQL*Net to client
385 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
14 rows processedSQL> select * from test2
2 where ename = 'SMITH'; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- ------------------- ---------- ---------- ----------
7369 SMITH CLERK 7902 1980-12-17 00:00:00 800 20
Execution Plan
----------------------------------------------------------
Plan hash value: 300966803---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 87 | 3 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| TEST2 | 1 | 87 | 3 (0)| 00:00:01 |
---------------------------------------------------------------------------Predicate Information (identified by operation id):
--------------------------------------------------- 1 - filter("ENAME"='SMITH')Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
5 recursive calls
0 db block gets
8 consistent gets
0 physical reads
0 redo size
822 bytes sent via SQL*Net to client
385 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processedSQL> create index ind_ename_test2 on test2(ename); Index created.SQL> select * from test2
2 where ename = 'SMITH'; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- ------------------- ---------- ---------- ----------
7369 SMITH CLERK 7902 1980-12-17 00:00:00 800 20
Execution Plan
----------------------------------------------------------
Plan hash value: 923399397-----------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 87 | 2 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| TEST2 | 1 | 87 | 2 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | IND_ENAME_TEST2 | 1 | | 1 (0)| 00:00:01 |
-----------------------------------------------------------------------------------------------Predicate Information (identified by operation id):
--------------------------------------------------- 2 - access("ENAME"='SMITH')Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
9 recursive calls
0 db block gets
9 consistent gets
0 physical reads
0 redo size
826 bytes sent via SQL*Net to client
385 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processedSQL> select * from test2
2 where ename like '%SMITH'; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- ------------------- ---------- ---------- ----------
7369 SMITH CLERK 7902 1980-12-17 00:00:00 800 20
Execution Plan
----------------------------------------------------------
Plan hash value: 300966803---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 87 | 3 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| TEST2 | 1 | 87 | 3 (0)| 00:00:01 |
---------------------------------------------------------------------------Predicate Information (identified by operation id):
--------------------------------------------------- 1 - filter("ENAME" LIKE '%SMITH')Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
5 recursive calls
0 db block gets
8 consistent gets
0 physical reads
0 redo size
822 bytes sent via SQL*Net to client
385 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed这是一个简单的例子,只是说明区别,实际上索引的使用条件还有很多影响