VIEW中的Oracle SQL Reuse子查询

我正在尝试设置一个可能包含1000个记录的视图.某些字段需要子查询,这些子查询返回完全相同的数据.我想知道我是否可以在视图中查询一次,而不是每次都运行它.

下面是一些示例表/数据：

DROP VIEW MYVIEW;
DROP TABLE MYTABLE;
DROP TABLE MYTABLE_PARENT;

-- TABLES FOR VIEW
CREATE TABLE MYTABLE_PARENT ( PRIMARY_KEY NUMBER PRIMARY KEY );
CREATE TABLE MYTABLE ( PRIMARY_KEY NUMBER,MYVAL VARCHAR(255),PARENT_PRIMARY_KEY NUMBER);
INSERT INTO MYTABLE_PARENT VALUES (1);
INSERT INTO MYTABLE_PARENT VALUES (2);
INSERT INTO MYTABLE VALUES (1,'MYVAL1-1',1);
INSERT INTO MYTABLE VALUES (2,'MYVAL1-2',1);
INSERT INTO MYTABLE VALUES (3,'MYVAL2-1',2);

-- VIEW
CREATE OR REPLACE FORCE VIEW MYVIEW AS 
  SELECT CS.PRIMARY_KEY AS PARENT_PK,-- THE BELOW STATEMENTS REUSE THE SAME INNER SUBQUERY,IF THE 
  -- VIEW CONTAINS 1000 ROWS,THE INNER SUBQUERY WILL BE EXECUTED 
  -- 1000 TIMES,RETURNING THE SAME DATA EACH TIME.
  (SELECT PRIMARY_KEY FROM MYTABLE WHERE MYVAL = 'MYVAL1-1' AND 
  PARENT_PRIMARY_KEY = (SELECT PRIMARY_KEY FROM MYTABLE_PARENT 
  WHERE PRIMARY_KEY = CS.PRIMARY_KEY)) AS OUTPUT_VAL_1,(SELECT PRIMARY_KEY FROM MYTABLE WHERE MYVAL = 'MYVAL1-2' AND 
  PARENT_PRIMARY_KEY = (SELECT PRIMARY_KEY FROM MYTABLE_PARENT 
  WHERE PRIMARY_KEY = CS.PRIMARY_KEY)) AS OUTPUT_VAL_2
-- DEFINE CS
  FROM MYTABLE_PARENT CS;

SELECT * FROM MYVIEW;

select语句的结果如下：

PARENT_PK              OUTPUT_VAL_1           OUTPUT_VAL_2           
---------------------- ---------------------- ---------------------- 
1                      1                      2                      
2

因此,在上面的查询中,我想对视图中的每一行只运行一次以下查询：

(SELECT PRIMARY_KEY FROM MYTABLE_PARENT WHERE PRIMARY_KEY = CS.PRIMARY_KEY)

有没有办法在视图中优化内部子查询？

解决方法

CREATE OR REPLACE FORCE VIEW MYVIEW AS 
  SELECT CS.PRIMARY_KEY AS PARENT_PK,MAX(DECODE(MT.MYVAL,MT.PRIMARY_KEY,TO_NUMBER(NULL))
                        AS OUTPUT_VAL_1,TO_NUMBER(NULL))
                        AS OUTPUT_VAL_2
  FROM MYTABLE_PARENT CS
  LEFT JOIN MYTABLE MT ON MT.PARENT_PRIMARY_KEY = CS.PRIMARY_KEY AND
                          MT.MYVAL IN ('MYVAL1-1','MYVAL1-2')
  GROUP BY CS.PRIMARY_KEY

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