本篇内容介绍了“Oracle中关于外键缺少索引的原因是什么”的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！
在ORACLE数据库中，定义外键约束时，ORACLE是不会自动创建对应索引的，必须手动在外键约束相关的列上创建索引。那么外键字段上是否有必要创建索引呢?如果有必要的话，巡检时，如何找出外键字段上没有创建索引的相关表，并生成对应的索引的脚本呢?
外键缺失索引的影响
外键列上缺少索引会带来三个问题，限制并发性、影响性能、还有可能造成死锁。所以对于绝大部分场景，我们应该尽量考虑在外键上面创建索引
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影响性能。如果子表外键没有创建索引，那么当父表查询关联子表时，子表将进行全表扫描。影响表连接方式。
影响并发。无论是更新父表主键，或者删除一个父记录，都会在子表中加一个表锁(在这条语句完成前，不允许对子表做任何修改)。这就会不必要地锁定更多的行，而影响并发性
在特殊情况下，还有可能造成死锁。
我们先来看看一个简单的例子，看看当外键缺失索引时，子表是否进行全表扫描，如下所示，表EMP与DEPT存在主外键关系：
SQL> set autotrace on; SQL> SQL> SELECT D.DEPTNO, COUNT(*) 2 FROM SCOTT.EMP E INNER JOIN SCOTT.DEPT D ON E.DEPTNO =D.DEPTNO 3 GROUP BY D.DEPTNO; DEPTNO COUNT(*) ---------- ---------- 30 6 20 5 10 3 Execution Plan ---------------------------------------------------------- Plan hash value: 4067220884 --------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 3 | 9 | 4 (25)| 00:00:01 | | 1 | HASH GROUP BY | | 3 | 9 | 4 (25)| 00:00:01 | |* 2 | TABLE ACCESS FULL| EMP | 14 | 42 | 3 (0)| 00:00:01 | --------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - filter("E"."DEPTNO" IS NOT NULL) Statistics ---------------------------------------------------------- 1 recursive calls 0 db block gets 7 consistent gets 0 physical reads 0 redo size 665 bytes sent via SQL*Net to client 524 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 3 rows processed
如上所示，当外键字段没有索引时，父表与子表关联时，子表会进行全表扫描，下面，我在外键字段创建索引后，就能避免子表表扫描了。
CREATE INDEX SCOTT.IX_DEPTNO ON SCOTT.EMP ("DEPTNO") TABLESPACE USERS;
当然这两个表的数据量实在是太少了，性能上差别不大，当数据量增长上去后，这个性能差异就会比较明显了。如下例子所示，我们构造一个数据量相对较大的父表与子表的案例：
create table parent_tb_test ( id number(10), name varchar2(32), constraint pk_parent_tb_test primary key(id) ); create table child_tb_test ( c_id number(10), f_id number(10), child_name varchar2(32), constraint pk_child_tb_test primary key(c_id), foreign key(f_id) references parent_tb_test ); begin for index_num in 1 .. 10000 loop insert into parent_tb_test select index_num , 'kerry' || to_char(index_num) from dual; if mod(index_num,100) = 0 then commit; end if; end loop; commit; end; / declare index_num number :=1; begin for index_parent in 1 .. 10000 loop for index_child in 1 .. 1000 loop insert into child_tb_test select index_num, index_parent, 'child' || to_char(index_child) from dual; index_num := index_num +1; if mod(index_child,1000) = 0 then commit; end if; end loop; end loop; commit; end; / SQL> execute dbms_stats.gather_table_stats(ownname => 'TEST', tabname =>'PARENT_TB_TEST', estimate_percent =>DBMS_STATS.AUTO_SAMPLE_SIZE, method_opt => 'FOR ALL COLUMNS SIZE AUTO'); PL/SQL procedure successfully completed. SQL> execute dbms_stats.gather_table_stats(ownname => 'TEST', tabname =>'CHILD_TB_TEST', estimate_percent =>DBMS_STATS.AUTO_SAMPLE_SIZE, method_opt => 'FOR ALL COLUMNS SIZE AUTO'); PL/SQL procedure successfully completed. SQL>
上面脚本构造了测试用的例子和数据， 那么我们对比看看外键有无索引的区别：
SQL> set linesize 1200 SQL> set autotrace traceonly SQL> select p.id , p.name,c.child_name 2 from test.parent_tb_test p 3 inner join test.child_tb_test c on p.id = c.f_id 4 where p.id=1000; 1000 rows selected. Execution Plan ---------------------------------------------------------- Plan hash value: 901213199 -------------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1009 | 44396 | 4706 (21)| 00:00:07 | | 1 | NESTED LOOPS | | 1009 | 44396 | 4706 (21)| 00:00:07 | | 2 | TABLE ACCESS BY INDEX ROWID| PARENT_TB_TEST | 1 | 31 | 1 (0)| 00:00:01 | |* 3 | INDEX UNIQUE SCAN | PK_PARENT_TB_TEST | 1 | | 1 (0)| 00:00:01 | |* 4 | TABLE ACCESS FULL | CHILD_TB_TEST | 1009 | 13117 | 4705 (21)| 00:00:07 | -------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 3 - access("P"."ID"=1000) 4 - filter("C"."F_ID"=1000) Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 32855 consistent gets 32772 physical reads 0 redo size 29668 bytes sent via SQL*Net to client 1218 bytes received via SQL*Net from client 68 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1000 rows processed SQL>
创建索引后，我们再来看看其执行计划，注意对比创建索引前后，执行计划的差异，如下所示：
SQL> create index ix_child_tb_test on child_tb_test(f_id); SQL> set linesize 1200 SQL> set autotrace traceonly SQL> select p.id , p.name,c.child_name 2 from test.parent_tb_test p 3 inner join test.child_tb_test c on p.id = c.f_id 4 where p.id=1000;
接下来，我们再来看看外键缺失索引影响并发，以及造成死锁的情况，如下所示，创建表dead_lock_parent与dead_lock_foreign，两者存在主外键关系，分布插入两条测试数据：
SQL> create table dead_lock_parent( id number primary key, name varchar2(32)); Table created. SQL> create table dead_lock_foreign(fid number, fname varchar2(32), foreign key(fid) references dead_lock_parent); Table created. SQL> insert into dead_lock_parent values( 1, 'kerry'); 1 row created. SQL> insert into dead_lock_foreign values(1, 'kerry_fk'); 1 row created. SQL> insert into dead_lock_parent values(2, 'jimmy'); 1 row created. SQL> insert into dead_lock_foreign values(2, 'jimmy_fk'); 1 row created. SQL> commit; Commit complete. SQL>
1：在会话1(会话ID为789)里面执行下面SQL语句：
SQL> show user; USER 为 "TEST" SQL> select * from v$mystat where rownum=1; SID STATISTIC# VALUE ---------- ---------- ---------- 789 0 1 SQL> delete from dead_lock_foreign where fid=1; 已删除 1 行。
2：在会话2(会话ID为766)里面执行下面SQL语句：
SQL> show user; USER is "TEST" SQL> select * from v$mystat where rownum=1; SID STATISTIC# VALUE ---------- ---------- ---------- 766 0 1 SQL> delete from dead_lock_foreign where fid=2; 1 row deleted.
3：接着在会话1(会话ID为789)里执行删除dead_lock_parent中id为1的记录：
SQL> delete from dead_lock_parent where id=1;
此时你会发现会话被阻塞了，我们可以用下面SQL查询具体的阻塞信息。
COL MODE_HELD FOR A14; COL LOCK_TYPE FOR A8; COL MODE_REQUESTED FOR A10; COL OBJECT_TYPE FOR A14; COL OBJECT_NAME FOR A20; SELECT LK.SID, DECODE(LK.TYPE, 'TX', 'Transaction', 'TM', 'DML', 'UL', 'PL/SQL User Lock', LK.TYPE) LOCK_TYPE, DECODE(LK.LMODE, 0, 'None', 1, 'Null', 2, 'Row-S (SS)', 3, 'Row-X (SX)', 4, 'Share', 5, 'S/Row-X (SSX)', 6, 'Exclusive', TO_CHAR(LK.LMODE)) MODE_HELD, DECODE(LK.REQUEST, 0, 'None', 1, 'Null', 2, 'Row-S (SS)', 3, 'Row-X (SX)', 4, 'Share', 5, 'S/Row-X (SSX)', 6, 'Exclusive', TO_CHAR(LK.REQUEST)) MODE_REQUESTED, OB.OBJECT_TYPE, OB.OBJECT_NAME, LK.BLOCK, SE.LOCKWAIT FROM V$LOCK LK, DBA_OBJECTS OB, V$SESSION SE WHERE LK.TYPE IN ('TM', 'UL') AND LK.SID = SE.SID AND LK.ID1 = OB.OBJECT_ID(+) AND SE.SID IN (766,789) ORDER BY SID;
上面信息如果不能让你理解，那么可以看看下面脚本，相信你能看得更详细。
SQL> SELECT S.SID SID, S.USERNAME USERNAME, S.MACHINE MACHINE, L.TYPE TYPE, O.OBJECT_NAME OBJECT_NAME, DECODE(L.LMODE, 0, 'None', 1, 'Null', 2, 'Row Share', 3, 'Row Exlusive', 4, 'Share', 5, 'Sh/Row Exlusive', 6, 'Exclusive') lmode, DECODE(L.REQUEST, 0, 'None', 1, 'Null', 2, 'Row Share', 3, 'Row Exlusive', 4, 'Share', 5, 'Sh/Row Exlusive', 6, 'Exclusive') request, L.BLOCK BLOCK FROM V$LOCK L, V$SESSION S, DBA_OBJECTS O WHERE L.SID = S.SID AND USERNAME != 'SYSTEM' AND O.OBJECT_ID(+) = L.ID1 AND S.SID IN ( 766,789) ORDER BY S.SID; SID USERNAME MACHINE TY OBJECT_NAME LMODE REQUEST BLOCK ---------- -------- -------------- -- -------------------- --------------- --------------- ----- 766 TEST XXXX\GET253194 TX Exclusive None 0 766 TEST XXXX\GET253194 TM DEAD_LOCK_FOREIGN Row Exlusive None 1 766 TEST XXXX\GET253194 TM DEAD_LOCK_PARENT Row Exlusive None 0 789 TEST DB-Server.loca TX Exclusive None 0 ldomain 789 TEST DB-Server.loca TM DEAD_LOCK_PARENT Row Exlusive None 0 ldomain 789 TEST DB-Server.loca TM DEAD_LOCK_FOREIGN Row Exlusive Sh/Row Exlusive 0 ldomain
接着在会话2里面执行下面SQL，删除主表中id=2的记录
SQL> delete from dead_lock_parent where id=2;
你会发现会话1就会出现Deadlock
如果你在外键字段上创建索引，那么这种情况下的操作就不会出现死锁。在这里就不再赘述。有兴趣可以测试一下.
外键创建索引建议(Foreign Key Indexing Tips)
虽然增加索引，可能会带来一些额外的性能开销(DML操作开销增加)和磁盘空间方面的开销，但是相比其带来的性能改善而言，这些额外的开销其实完全可以忽略。如果没有其他特殊情况，建议所有的外键字段都加上索引。在Oracle Oracle Database 9i/10g/11g编程艺术这本书中介绍了在什么时候不需要对外键加索引. 必须满足下面三个条件：
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不会删除父表中的行。
不论是有意还是无意，总之不会更新父表的唯一/主键字段值。
不会从父表联结到子表， 或者更通俗的讲，外键列不支持子表的一个重要访问路径，而且你在谓词中没有使用这些外键累从子表中选择数据。
找出未索引的外键
我们首先可以通过下面脚本，找到整个数据库中那些表有主外键关系，并列出主外键约束.
--查看整个数据库下拥有主外键关系的所有表(排除一些系统用户)
--查看整个数据库下拥有主外键关系的所有表（排除一些系统用户） SELECT DC.OWNER AS "PARENT_TABLE_OWNER", DC.TABLE_NAME AS "PARENT_TABLE_NAME", DC.CONSTRAINT_NAME AS "PRIMARY CONSTRAINT NAME", DF.CONSTRAINT_NAME AS "REFERENCED CONSTRAINT NAME", DF.OWNER AS "CHILD_TABLE_OWNER", DF.TABLE_NAME AS "CHILD_TABLE_NAME" FROM DBA_CONSTRAINTS DC, (SELECT C.OWNER, C.CONSTRAINT_NAME, C.R_CONSTRAINT_NAME, C.TABLE_NAME FROM DBA_CONSTRAINTS C WHERE CONSTRAINT_TYPE = 'R') DF WHERE DC.CONSTRAINT_NAME =DF.R_CONSTRAINT_NAME AND DC.OWNER NOT IN ( 'SYSTEM', 'SYS', 'DBSNMP', 'EXFSYS', 'ORDDATA', 'CTXSYS', 'OLAPSYS', 'MDSYS', 'SYSMAN' );
--查看某个Schema下拥有主外键关系的所有表
--查看某个Schema下拥有主外键关系的所有表 SELECT DC.OWNER AS "PARENT_TABLE_OWNER", DC.TABLE_NAME AS "PARENT_TABLE_NAME", DC.CONSTRAINT_NAME AS "PRIMARY CONSTRAINT NAME", DF.CONSTRAINT_NAME AS "REFERENCED CONSTRAINT NAME", DF.OWNER AS "CHILD_TABLE_OWNER", DF.TABLE_NAME AS "CHILD_TABLE_NAME" FROM DBA_CONSTRAINTS DC, (SELECT C.OWNER, C.CONSTRAINT_NAME, C.R_CONSTRAINT_NAME, C.TABLE_NAME FROM DBA_CONSTRAINTS C WHERE CONSTRAINT_TYPE = 'R') DF WHERE DC.CONSTRAINT_NAME = DF.R_CONSTRAINT_NAME AND DC.OWNER =UPPER('&OWNER');--查看某个具体的表是否和其它表拥有主外键关系
--查看某个具体的表是否和其它表拥有主外键关系 SELECT DC.OWNER AS "PARENT_TABLE_OWNER", DC.TABLE_NAME AS "PARENT_TABLE_NAME", DC.CONSTRAINT_NAME AS "PRIMARY CONSTRAINT NAME", DF.CONSTRAINT_NAME AS "REFERENCED CONSTRAINT NAME", DF.OWNER AS "CHILD_TABLE_OWNER", DF.TABLE_NAME AS "CHILD_TABLE_NAME" FROM DBA_CONSTRAINTS DC, (SELECT C.OWNER, C.CONSTRAINT_NAME, C.R_CONSTRAINT_NAME, C.TABLE_NAME FROM DBA_CONSTRAINTS C WHERE CONSTRAINT_TYPE = 'R') DF WHERE DC.CONSTRAINT_NAME = DF.R_CONSTRAINT_NAME AND DC.OWNER =UPPER('&OWNER') AND DC.TABLE_NAME=UPPER('&TABLE_NAME');接下来我们要找出在具体的外键字段是否有索引，脚本如下所示：
SELECT CON.OWNER , CON.TABLE_NAME, CON.CONSTRAINT_NAME, CON.COL_LIST, 'No Indexed' AS INDEX_STATUS FROM (SELECT CC.OWNER, CC.TABLE_NAME, CC.CONSTRAINT_NAME, MAX(DECODE(POSITION, 1, '"' || SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(POSITION, 2,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(POSITION, 3,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(POSITION, 4,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(POSITION, 5,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(POSITION, 6,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(POSITION, 7,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(POSITION, 8,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(POSITION, 9,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(POSITION, 10,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) COL_LIST FROM DBA_CONSTRAINTS DC, DBA_CONS_COLUMNS CC WHERE DC.OWNER = CC.OWNER AND DC.CONSTRAINT_NAME = CC.CONSTRAINT_NAME AND DC.CONSTRAINT_TYPE = 'R' AND DC.OWNER NOT IN ('SYS', 'SYSTEM', 'OLAPSYS', 'SYSMAN', 'MDSYS', 'ADMIN') GROUP BY CC.OWNER, CC.TABLE_NAME, CC.CONSTRAINT_NAME ) CON WHERE NOT EXISTS ( SELECT 1 FROM ( SELECT TABLE_OWNER, TABLE_NAME, MAX(DECODE(COLUMN_POSITION, 1, '"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(COLUMN_POSITION, 2,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(COLUMN_POSITION, 3,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(COLUMN_POSITION, 4,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(COLUMN_POSITION, 5,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(COLUMN_POSITION, 6,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(COLUMN_POSITION, 7,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(COLUMN_POSITION, 8,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(COLUMN_POSITION, 9,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(COLUMN_POSITION, 10,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) COL_LIST FROM DBA_IND_COLUMNS WHERE TABLE_OWNER NOT IN ('SYS', 'SYSTEM', 'OLAPSYS', 'SYSMAN', 'MDSYS') GROUP BY TABLE_OWNER, TABLE_NAME, INDEX_NAME ) COL WHERE CON.OWNER = COL.TABLE_OWNER AND CON.TABLE_NAME = COL.TABLE_NAME AND CON.COL_LIST = SUBSTR(COL.COL_LIST, 1, LENGTH(CON.COL_LIST) ) ) ;如果是ORACLE 11g或以上版本，数据库有分析函数LISTAGG的话，可以使用下面脚本
SELECT CASE WHEN B.TABLE_NAME IS NULL THEN 'NO INDEXED' ELSE 'INDEXED' END AS STATUS, A.TABLE_OWNER AS TABLE_OWNER, A.TABLE_NAME AS TABLE_NAME, A.CONSTRAINT_NAME AS FK_NAME, A.FK_COLUMNS AS FK_COLUMNS, B.INDEX_NAME AS INDEX_NAME, B.INDEX_COLUMNS AS INDEX_COLUMNS FROM (SELECT A.OWNER AS TABLE_OWNER, A.TABLE_NAME AS TABLE_NAME, A.CONSTRAINT_NAME AS CONSTRAINT_NAME, LISTAGG(A.COLUMN_NAME, ',') WITHIN GROUP (ORDER BY A.POSITION) FK_COLUMNS FROM DBA_CONS_COLUMNS A, DBA_CONSTRAINTS B WHERE A.CONSTRAINT_NAME = B.CONSTRAINT_NAME AND B.CONSTRAINT_TYPE = 'R' AND A.OWNER = B.OWNER AND A.OWNER NOT IN ( 'SYS', 'SYSTEM', 'OLAPSYS', 'SYSMAN', 'MDSYS' ) GROUP BY A.OWNER, A.TABLE_NAME, A.CONSTRAINT_NAME) A, (SELECT TABLE_OWNER, TABLE_NAME, INDEX_NAME, LISTAGG(C.COLUMN_NAME, ',') WITHIN GROUP (ORDER BY C.COLUMN_POSITION) INDEX_COLUMNS FROM DBA_IND_COLUMNS C GROUP BY TABLE_OWNER, TABLE_NAME, INDEX_NAME) B WHERE A.TABLE_NAME = B.TABLE_NAME(+) AND A.TABLE_OWNER = B.TABLE_OWNER(+) AND B.INDEX_COLUMNS(+) LIKE A.FK_COLUMNS || '%' ORDER BY 1 DESC
自动生成创建外键索引的脚本
上面的这些脚本已经能找出那些外键字段已经建立或未建立索引，此时如果对外键字段缺少索引的表手工创建索引的话，如果数量很多的话，那么工作量也非常大，下面可以用这个脚本自动生成缺失的索引
/******************************************************************************************* --脚本功能描述： -- 对于数据库中外键缺少索引的字段，生成对应的索引（排除一些系统账号，例如sys、system）,如果外键索引超过十个字段 -- 那么这个脚本就不能正确的生成对应的索引，当然也很少有外键设置在超过10个字段的。另外索引表空 -- 空间跟数据表空间相同，如有分开的话，建议在此处再做调整。 ********************************************************************************************/ SELECT 'CREATE INDEX ' || OWNER || '.' || REPLACE(CONSTRAINT_NAME,'FK_','IX_') || ' ON ' || OWNER || '.' || TABLE_NAME || ' (' || COL_LIST ||') TABLESPACE ' || (SELECT TABLESPACE_NAME FROM DBA_TABLES WHERE OWNER= CON.OWNER AND TABLE_NAME= CON.TABLE_NAME) AS CREATE_INDEXES_ON_FOREIGN_KEY FROM (SELECT CC.OWNER, CC.TABLE_NAME, CC.CONSTRAINT_NAME, MAX(DECODE(POSITION, 1, '"' || SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(POSITION, 2,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(POSITION, 3,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(POSITION, 4,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(POSITION, 5,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(POSITION, 6,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(POSITION, 7,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(POSITION, 8,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(POSITION, 9,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(POSITION, 10,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) COL_LIST FROM DBA_CONSTRAINTS DC, DBA_CONS_COLUMNS CC WHERE DC.OWNER = CC.OWNER AND DC.CONSTRAINT_NAME = CC.CONSTRAINT_NAME AND DC.CONSTRAINT_TYPE = 'R' AND DC.OWNER NOT IN ('SYS', 'SYSTEM', 'OLAPSYS', 'SYSMAN', 'MDSYS', 'ADMIN') GROUP BY CC.OWNER, CC.TABLE_NAME, CC.CONSTRAINT_NAME ) CON WHERE NOT EXISTS ( SELECT 1 FROM ( SELECT TABLE_OWNER, TABLE_NAME, MAX(DECODE(COLUMN_POSITION, 1, '"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(COLUMN_POSITION, 2,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(COLUMN_POSITION, 3,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(COLUMN_POSITION, 4,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(COLUMN_POSITION, 5,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(COLUMN_POSITION, 6,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(COLUMN_POSITION, 7,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(COLUMN_POSITION, 8,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(COLUMN_POSITION, 9,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) || MAX(DECODE(COLUMN_POSITION, 10,', '||'"'|| SUBSTR(COLUMN_NAME,1,30) ||'"',NULL)) COL_LIST FROM DBA_IND_COLUMNS WHERE TABLE_OWNER NOT IN ('SYS', 'SYSTEM', 'OLAPSYS', 'SYSMAN', 'MDSYS') GROUP BY TABLE_OWNER, TABLE_NAME, INDEX_NAME ) COL WHERE CON.OWNER = COL.TABLE_OWNER AND CON.TABLE_NAME = COL.TABLE_NAME AND CON.COL_LIST = SUBSTR(COL.COL_LIST, 1, LENGTH(CON.COL_LIST) ) ) ;--脚本使用分析函数LISTAGG， 适用于ORACLE 11g以及以上版本，如果数据库版本是Oracle 11g及以上，就可以使用此脚本替代上面脚本。
SELECT 'CREATE INDEX ' || OWNER || '.' || REPLACE(CONSTRAINT_NAME,'FK_','IX_') || ' ON ' || OWNER || '.' || TABLE_NAME || ' (' || FK_COLUMNS ||') TABLESPACE ' || ( SELECT TABLESPACE_NAME FROM DBA_TABLES WHERE OWNER= CON.OWNER AND TABLE_NAME= CON.TABLE_NAME) CREATE_INDEXES_ON_FOREIGN_KEY FROM ( SELECT CC.OWNER, CC.TABLE_NAME, CC.CONSTRAINT_NAME, LISTAGG(CC.COLUMN_NAME, ',') WITHIN GROUP (ORDER BY CC.POSITION) FK_COLUMNS FROM DBA_CONS_COLUMNS CC, DBA_CONSTRAINTS DC WHERE CC.CONSTRAINT_NAME = DC.CONSTRAINT_NAME AND DC.CONSTRAINT_TYPE = 'R' AND CC.OWNER = DC.OWNER AND DC.OWNER NOT IN ( 'SYS', 'SYSTEM', 'OLAPSYS', 'SYSMAN', 'MDSYS', 'ADMIN' ) GROUP BY CC.OWNER, CC.TABLE_NAME, CC.CONSTRAINT_NAME) CON WHERE NOT EXISTS ( SELECT 1 FROM ( SELECT TABLE_OWNER, TABLE_NAME, INDEX_NAME, LISTAGG(COLUMN_NAME, ',') WITHIN GROUP (ORDER BY COLUMN_POSITION) FK_COLUMNS FROM DBA_IND_COLUMNS WHERE INDEX_OWNER NOT IN ( 'SYS', 'SYSTEM', 'OLAPSYS', 'SYSMAN', 'MDSYS', 'ADMIN' ) GROUP BY TABLE_OWNER, TABLE_NAME ,INDEX_NAME) COL WHERE CON.OWNER = COL.TABLE_OWNER AND CON.TABLE_NAME = COL.TABLE_NAME AND CON.FK_COLUMNS = SUBSTR(COL.FK_COLUMNS, 1, LENGTH(CON.FK_COLUMNS)) ) ORDER BY 1;“Oracle中关于外键缺少索引的原因是什么”的内容就介绍到这里了，感谢大家的阅读。如果想了解更多行业相关的知识可以关注亿速云网站，小编将为大家输出更多高质量的实用文章！
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