union和union all图式

1. union:

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1.    SELECT * FROM emp 

2.    WHERE sal < 1500 

3.    UNION 

4.    SELECT * FROM emp 

5.    WHERE sal  BETWEEN 1000 AND 2000 

6.    ORDER BY 1;  

 

 

 

2. union all:

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1.    SELECT * FROM emp 

2.    WHERE sal < 1500 

3.    UNION ALL ORACLE OCP

4.    SELECT * FROM emp 

5.    WHERE sal  BETWEEN 1000 AND 2000 

6.    ORDER BY 1;