SQLite 别名
SQLite 别名
我们可以通过给一个表或列取另一个名字来临时重命名,这个操作叫做别名。使用表别名意味着重命名特定SQLite语句中的表。重命名是临时更改,数据库中的实际表名不会更改。
列别名用于为特定SQLite查询重命名表的列。
语法
SELECT column1, column2.... FROM table_name AS alias_name WHERE [condition];
以下是列别名的基本语法。
SELECT column_name AS alias_name FROM table_name WHERE [condition];
例子
假设有两张表,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
另外一张表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
下面是ALIAS的用法,我们分别使用C和D作为COMPANY和DEPARTMENT表的别名
sqlite> SELECT C.ID, C.NAME, C.AGE, D.DEPT FROM COMPANY AS C, DEPARTMENT AS D WHERE C.ID = D.EMP_ID;
上述SQLite语句将产生以下结果:
ID NAME AGE DEPT ---------- ---------- ---------- ---------- 1 Paul 32 IT Billing 2 Allen 25 Engineering 3 Teddy 23 Engineering 4 Mark 25 Finance 5 David 27 Engineering 6 Kim 22 Finance 7 James 24 Finance
考虑列别名的使用示例,其中COMPANY_ID是ID列的别名,COMPANY_NAME是NAME列的别名。
sqlite> SELECT C.ID AS COMPANY_ID, C.NAME AS COMPANY_NAME, C.AGE, D.DEPT FROM COMPANY AS C, DEPARTMENT AS D WHERE C.ID = D.EMP_ID;
上述SQLite语句将产生以下结果:
COMPANY_ID COMPANY_NAME AGE DEPT ---------- ------------ ---------- ---------- 1 Paul 32 IT Billing 2 Allen 25 Engineering 3 Teddy 23 Engineering 4 Mark 25 Finance 5 David 27 Engineering 6 Kim 22 Finance 7 James 24 Finance