Union 子句

Union 子句

UNION 子句/运算符用于合并两个或多个 SELECT 语句的结果，不返回任何重复的行。

为了使用 UNION，每个 SELECT 被选择的列数必须是相同的，相同数目的列表达式，相同的数据类型，并确保它们有相同的顺序，但它们不必具有相同的长度。

SELECT column1 [, column2 ]
FROM table1 [, table2 ]
[WHERE condition]

UNION

SELECT column1 [, column2 ]
FROM table1 [, table2 ]
[WHERE condition]

实例

-- 数据准备
sqlite> select * from COMPANY ;
ID          NAME        AGE         ADDRESS     SALARY
----------  ----------  ----------  ----------  ----------
1           Paul        32          California  20000.0
2           Allen       25          Texas       15000.0
3           Teddy       23          Norway      20000.0
4           Mark        25          Rich-Mond   65000.0
5           David       27          Texas       85000.0
6           Kim         22          South-Hall  45000.0
7           James       24          Houston     10000.0
sqlite>
sqlite> select * from DEPARTMENT ;
ID          DEPT        EMP_ID
----------  ----------  ----------
1           IT Billing  1
2           Engineerin  2
3           Finance     7
4           Engineerin  3
5           Finance     4
6           Engineerin  5
7           Finance     6

sqlite> SELECT EMP_ID, NAME, DEPT FROM COMPANY INNER JOIN DEPARTMENT
   ...>         ON COMPANY.ID = DEPARTMENT.EMP_ID
   ...>    UNION
   ...>      SELECT EMP_ID, NAME, DEPT FROM COMPANY LEFT OUTER JOIN DEPARTMENT
   ...>         ON COMPANY.ID = DEPARTMENT.EMP_ID;
EMP_ID      NAME        DEPT
----------  ----------  ----------
1           Paul        IT Billing
2           Allen       Engineerin
3           Teddy       Engineerin
4           Mark        Finance
5           David       Engineerin
6           Kim         Finance
7           James       Finance

UNION ALL 子句

UNION ALL 运算符用于结合两个 SELECT 语句的结果，包括重复行。

适用于 UNION 的规则同样适用于 UNION ALL 运算符。

SELECT column1 [, column2 ]
FROM table1 [, table2 ]
[WHERE condition]

UNION ALL

SELECT column1 [, column2 ]
FROM table1 [, table2 ]
[WHERE condition]

实例

sqlite> SELECT EMP_ID, NAME, DEPT FROM COMPANY INNER JOIN DEPARTMENT
   ...>         ON COMPANY.ID = DEPARTMENT.EMP_ID
   ...>    UNION ALL
   ...>      SELECT EMP_ID, NAME, DEPT FROM COMPANY LEFT OUTER JOIN DEPARTMENT
   ...>         ON COMPANY.ID = DEPARTMENT.EMP_ID;
EMP_ID      NAME        DEPT
----------  ----------  ----------
1           Paul        IT Billing
2           Allen       Engineerin
7           James       Finance
3           Teddy       Engineerin
4           Mark        Finance
5           David       Engineerin
6           Kim         Finance
1           Paul        IT Billing
2           Allen       Engineerin
3           Teddy       Engineerin
4           Mark        Finance
5           David       Engineerin
6           Kim         Finance
7           James       Finance