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SQLite UNIONS 子句

SQLite的UNION子句/運算符用於合並兩個或多個SELECT語句的結果,不返回任何重複的行。

直接使用UNION,每個SELECT選擇的列數必須具有相同的,相同數目的列表達式相同的數據類型,並讓它們在相同的順序,但它們不必具有相同的長度。

語法

UNION的基本語法如下:

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

UNION

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

這裡給定的條件可以是任何表達式,根據需要。

例子:

考慮以下兩個表:COMPANY表如下:

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

另一表是DEPARTMENT如下:

ID          DEPT                  EMP_ID
----------  --------------------  ----------
1           IT Billing            1
2           Engineering           2
3           Finance               7
4           Engineering           3
5           Finance               4
6           Engineering           5
7           Finance               6

現在,讓我們加入這兩個表使用SELECT語句一起UNION子句如下:

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;

這將產生以下結果:

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運算符是用來結合兩個SELECT語句,包括重複行的結果。

UNION 適用同樣的規則適用於UNION 所有操作符。

語法

UNION ALL的基本語法如下:

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

UNION ALL

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

這裡給定的條件可以是任何表達式,根據需要。

例子:

現在,讓我們連接上述兩個表中的SELECT語句如下:

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;

這將產生以下結果:

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
1           Paul                  IT Billing
2           Allen                 Engineerin
3           Teddy                 Engineerin
4           Mark                  Finance
5           David                 Engineerin
6           Kim                   Finance
7           James                 Finance