sqlite

Database; use; embedded relational database

unions

n. Union; Union plural noun); harmony; marriage

SQLite Unions function syntax

Function:SQLite's UNION clause/operator is used to combine the results of two or more SELECT statements without returning any duplicate rows.

In order to use UNION, the number of columns selected in each SELECT must be the same, the same number of column expressions, the same data type, and make sure they have the same order, but they do not have to have the same length .

Grammar: The basic syntax of UNION is as follows:

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

UNION

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

The conditions given here can be any expression as needed Mode.

SQLite Unions function example

COMPANY 表如下所示：

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
（2）另一个表是 DEPARTMENT，如下所示：

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
现在，让我们使用 SELECT 语句及 UNION 子句来连接两个表，如下所示：

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;
这将产生以下结果：

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