不少人大概和我一样在创建物化视图的时候会犯头痛，怎样合理的改写SQL语句以及添加物化视图日志需要经过慎重精密的考虑。有了DBMS_ADVISOR.TUNE_MVIEW存储过程这个帮手后，极大地方便了DBA或应用设计人员创建和优化物化视图。该TUNE_MVIEW存储过程可以做到优化物化视图中的查询定义，修正物化视图日志的问题，此外它还能为原先不能refresh fast的物化视图提出建议以使得其可以快速刷新。
SQL> CREATE MATERIALIZED VIEW MACLEAN.STRMTS
2 USING INDEX REFRESH FAST ON DEMAND
3 ENABLE QUERY REWRITE
4 AS select distinct t1,t2 from MACLEAN.strb;
AS select distinct t1,t2 from MACLEAN.strb
*
ERROR at line 4:
ORA-12015: cannot create a fast refresh materialized view from a complex query
/* 以select distinct查询语句为例，该语句本身不符合refresh fast的标准，但TUNE_MVIEW存储过程
可以将这种查询变形使得满足快速刷新的条件 */
-- PROCEDURE DBMS_ADVISOR.TUNE_MVIEW
-- PURPOSE: Tune a Create Materialized View statement to
-- ADVISOR SUPPORT: SQL Access Advisor
-- PARAMETERS:
-- TASK_NAME
-- The user can pass in a user-defined task name or
-- get a returned system-generated task name.
-- MV_CREATE_STMT
-- CREATE MATERIALIZED VIEW SQL statement to tune
procedure tune_mview (task_name in out varchar2,
mv_create_stmt in clob);
SQL> set serveroutput on;
SQL> declare
2 tn varchar2(200);
3 begin
4 DBMS_ADVISOR.TUNE_MVIEW(tn,
5 mv_create_stmt => 'CREATE MATERIALIZED VIEW MACLEAN.STRMTS
6 USING INDEX REFRESH FAST ON DEMAND
7 ENABLE QUERY REWRITE
8 AS select distinct t1,t2 from MACLEAN.strb');
9 dbms_output.put_line(tn);
10 end;
11 /
TASK_484
PL/SQL procedure successfully completed.
SQL> select script_type,statement
2 from dba_tune_mview
3 where task_name = 'TASK_484'
4 order by action_id;
SCRIPT_TYPE STATEMENT
IMPLEMENTATION CREATE MATERIALIZED VIEW LOG ON "MACLEAN"."STRB" WITH ROWID, SEQUENCE ("T1","T2") INCLUDING NEW VALUES
IMPLEMENTATION ALTER MATERIALIZED VIEW LOG FORCE ON "MACLEAN"."STRB" ADD ROWID, SEQUENCE ("T1","T2") INCLUDING NEW VALUES
IMPLEMENTATION CREATE MATERIALIZED VIEW MACLEAN.STRMTS USING INDEX REFRESH FAST WITH ROWID ENABLE QUERY REWRITE AS SELECT MACLEAN.STRB.T2 C1, MACLEAN.STRB.T1 C2, COUNT(*) M1 FROM MACLEAN.STRB GROUP BY MACLEAN.STRB.T2, MACLEAN.STRB.T1
UNDO DROP MATERIALIZED VIEW MACLEAN.STRMTS
/* 可以看到TUNE_MVIEW存储过程将原查询变形为SELECT...GROUP BY的形式 */
SQL> CREATE MATERIALIZED VIEW LOG ON "MACLEAN"."STRB" WITH ROWID, SEQUENCE ("T1","T2") INCLUDING NEW VALUES;
Materialized view log created.
SQL> ALTER MATERIALIZED VIEW LOG FORCE ON "MACLEAN"."STRB" ADD ROWID, SEQUENCE ("T1","T2") INCLUDING NEW VALUES;
Materialized view log altered.
SQL> CREATE MATERIALIZED VIEW MACLEAN.STRMTS USING INDEX REFRESH FAST WITH ROWID
ENABLE QUERY REWRITE AS SELECT MACLEAN.STRB.T2 C1, MACLEAN.STRB.T1 C2, COUNT(*) M1
FROM MACLEAN.STRB GROUP BY MACLEAN.STRB.T2, MACLEAN.STRB.T1;
Materialized view created.
针对那些确实无法快速刷新的复杂查询，TUNE_MVIEW过程也可能给出将一个查询分解为多个物化视图达到快速刷新和查询重写的目的:
SQL> CREATE MATERIALIZED VIEW MACLEAN.STRMTD
2 USING INDEX REFRESH FAST
3 ON DEMAND ENABLE QUERY REWRITE AS
4 select t2,t3,count(*) from strc group by t2,t3
5 union all
6 select t2,t3,count(*) from strd group by t2,t3;
select t2,t3,count(*) from strd group by t2,t3
*
ERROR at line 6:
ORA-12015: cannot create a fast refresh materialized view from a complex query
SQL> set serveroutput on;
SQL> declare
2 tn varchar2(200);
3 begin
4 DBMS_ADVISOR.TUNE_MVIEW(tn,
5 mv_create_stmt => 'CREATE MATERIALIZED VIEW MACLEAN.STRMTC
6 USING INDEX REFRESH FAST
7 ON DEMAND ENABLE QUERY REWRITE AS
8 select t2,t3,count(*) from strc group by t2,t3
9 union all
10 select t2,t3,count(*) from strd group by t2,t3');
11 dbms_output.put_line(tn);
12 end;
13 /
TASK_547
PL/SQL procedure successfully completed.
SQL> select statement
2 from dba_tune_mview
3 where task_name = 'TASK_547'
4 order by action_id;
CREATE MATERIALIZED VIEW LOG ON "MACLEAN"."STRC" WITH ROWID, SEQUENCE ("T2","T3") INCLUDING NEW VALUES
ALTER MATERIALIZED VIEW LOG FORCE ON "MACLEAN"."STRC" ADD ROWID, SEQUENCE ("T2","T3") INCLUDING NEW VALUES
CREATE MATERIALIZED VIEW LOG ON "MACLEAN"."STRD" WITH ROWID, SEQUENCE ("T2","T3") INCLUDING NEW VALUES
ALTER MATERIALIZED VIEW LOG FORCE ON "MACLEAN"."STRD" ADD ROWID, SEQUENCE ("T2","T3") INCLUDING NEW VALUES
CREATE MATERIALIZED VIEW MACLEAN.STRMTC$SUB1 USING INDEX REFRESH FAST WITH ROWID ON COMMIT ENABLE QUERY REWRITE AS SELECT MACLEAN.STRC.T3 C1, MACLEAN.STRC.T2 C2, COUNT(*) M1 FROM MACLEAN.STRC GROUP BY MACLEAN.STRC.T3, MACLEAN.STRC.T2
DROP MATERIALIZED VIEW MACLEAN.STRMTC$SUB1
CREATE MATERIALIZED VIEW MACLEAN.STRMTC$SUB2 USING INDEX REFRESH FAST WITH ROWID ON COMMIT ENABLE QUERY REWRITE AS SELECT MACLEAN.STRD.T3 C1, MACLEAN.STRD.T2 C2, COUNT(*) M1 FROM MACLEAN.STRD GROUP BY MACLEAN.STRD.T3, MACLEAN.STRD.T2
DROP MATERIALIZED VIEW MACLEAN.STRMTC$SUB2
CREATE MATERIALIZED VIEW MACLEAN.STRMTC USING INDEX REFRESH FORCE WITH ROWID ENABLE QUERY REWRITE AS (SELECT "STRMTC$SUB1"."C2" "T2","STRMTC$SUB1"."C1" "T3","STRMTC$SUB1"."M1" "COUNT(*)" FROM "MACLEAN"."STRMTC$SUB1" "STRMTC$SUB1") UNION ALL (SELECT "STRMTC$SUB2"."C2" "T2","STRMTC$SUB2"."C1" "T3","STRMTC$SUB2"."M1" "COUNT(*)" FROM "MACLEAN"."STRMTC$SUB2" "STRMTC$SUB2")
DROP MATERIALIZED VIEW MACLEAN.STRMTC
DBMS_ADVANCED_REWRITE.BUILD_SAFE_REWRITE_EQUIVALENCE ('MACLEAN.STRMTC$RWEQ','select t2,t3,count(*) from strc group by t2,t3
union all
select t2,t3,count(*) from strd group by t2,t3',' (SELECT "STRMTC$SUB1"."C2" "T2","STRMTC$SUB1"."C1" "T3","STRMTC$SUB1"."M1" "COUNT(*)" FROM "MACLEAN"."STRMTC$SUB1" "STRMTC$SUB1") UNION ALL (SELECT "STRMTC$SUB2"."C2" "T2","STRMTC$SUB2"."C1" "T3","STRMTC$SUB2"."M1" "COUNT(*)" FROM "MACLEAN"."STRMTC$SUB2" "STRMTC$SUB2")',600916906)
DBMS_ADVANCED_REWRITE.DROP_REWRITE_EQUIVALENCE('MACLEAN.STRMTC$RWEQ')
SQL> CREATE MATERIALIZED VIEW LOG ON "MACLEAN"."STRC" WITH ROWID, SEQUENCE ("T2","T3") INCLUDING NEW VALUES;
Materialized view log created.
SQL> ALTER MATERIALIZED VIEW LOG FORCE ON "MACLEAN"."STRC" ADD ROWID, SEQUENCE ("T2","T3") INCLUDING NEW VALUES;
Materialized view log altered.
SQL> CREATE MATERIALIZED VIEW LOG ON "MACLEAN"."STRD" WITH ROWID, SEQUENCE ("T2","T3") INCLUDING NEW VALUES;
Materialized view log created.
SQL> ALTER MATERIALIZED VIEW LOG FORCE ON "MACLEAN"."STRD" ADD ROWID, SEQUENCE ("T2","T3") INCLUDING NEW VALUES;
Materialized view log altered.
SQL> CREATE MATERIALIZED VIEW MACLEAN.STRMTC$SUB1 USING INDEX REFRESH FAST WITH ROWID
ON COMMIT ENABLE QUERY REWRITE AS SELECT MACLEAN.STRC.T3 C1, MACLEAN.STRC.T2 C2, COUNT(*) M1
FROM MACLEAN.STRC GROUP BY MACLEAN.STRC.T3, MACLEAN.STRC.T2;
Materialized view created.
SQL> CREATE MATERIALIZED VIEW MACLEAN.STRMTC$SUB2 USING INDEX REFRESH FAST WITH ROWID
ON COMMIT ENABLE QUERY REWRITE AS SELECT MACLEAN.STRD.T3 C1, MACLEAN.STRD.T2 C2, COUNT(*) M1
FROM MACLEAN.STRD GROUP BY MACLEAN.STRD.T3, MACLEAN.STRD.T2;
Materialized view created.
SQL> CREATE MATERIALIZED VIEW MACLEAN.STRMTC USING INDEX REFRESH FORCE WITH ROWID
ENABLE QUERY REWRITE AS
(SELECT "STRMTC$SUB1"."C2" "T2","STRMTC$SUB1"."C1" "T3","STRMTC$SUB1"."M1" "COUNT(*)" FROM "MACLEAN"."STRMTC$SUB1" "STRMTC$SUB1")
UNION ALL
(SELECT "STRMTC$SUB2"."C2" "T2","STRMTC$SUB2"."C1" "T3","STRMTC$SUB2"."M1" "COUNT(*)" FROM "MACLEAN"."STRMTC$SUB2" "STRMTC$SUB2");
Materialized view created.
declare
v_state varchar2(2000);
begin
select statement
into v_state
from dba_tune_mview
where task_name = 'TASK_547'
and action_id = 15;
v_state := 'begin ' || v_state || '; end;';
dbms_output.put_line(v_state);
execute immediate v_state;
end;
PL/SQL procedure successfully completed.
SQL> set linesize 200 pagesize 1400;
SQL> select t2,t3,count(*) from strc group by t2,t3
2 union all
3 select t2,t3,count(*) from strd group by t2,t3;
no rows selected
---------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2 | 74 | 4 (50)| 00:00:01 |
| 1 | UNION-ALL | | | | | |
| 2 | MAT_VIEW REWRITE ACCESS FULL| STRMTC$SUB1 | 1 | 37 | 2 (0)| 00:00:01 |
| 3 | MAT_VIEW REWRITE ACCESS FULL| STRMTC$SUB2 | 1 | 37 | 2 (0)| 00:00:01 |
---------------------------------------------------------------------------------------------
/* 可以看到查询成功被rewrite为对2个物化视图的扫描 */
