可以重命名表或列暂时给人的另一个名字,这被称为别名。使用表别名是指在一个特定的SQLite语句重命名表。重命名是一个临时的变化,并在数据库中实际的表的名称不会改变。
列别名用来重命名表中的列一个特定的SQLite查询的目的。
语法
表别名的基本语法如下:
SELECT column1, column2.... FROM table_name AS alias_name WHERE [condition];
列别名的基本语法如下:
SELECT column_name AS alias_name FROM table_name WHERE [condition];
例子:
考虑以下两个表:(一)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
(b)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
现在,下面是表的别名,在这里我们使用C和D分别为COMPANY和DEPARTMENT表的别名的用法:
sqlite> SELECT C.ID, C.NAME, C.AGE, D.DEPT FROM COMPANY AS C, DEPARTMENT AS D WHERE C.ID = D.EMP_ID;
以上SQLite的语句将产生以下结果:
ID NAME AGE DEPT ---------- ---------- ---------- ---------- 1 Paul 32 IT Billing 2 Allen 25 Engineerin 3 Teddy 23 Engineerin 4 Mark 25 Finance 5 David 27 Engineerin 6 Kim 22 Finance 7 James 24 Finance
让我们看一个例子company_id的是ID列的别名和COMPANY_NAME的别名name列字段的别名的用法:
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;
以上SQLite的语句将产生以下结果:
COMPANY_ID COMPANY_NAME AGE DEPT ---------- ------------ ---------- ---------- 1 Paul 32 IT Billing 2 Allen 25 Engineerin 3 Teddy 23 Engineerin 4 Mark 25 Finance 5 David 27 Engineerin 6 Kim 22 Finance 7 James 24 Finance