PostgreSQL 别名
我们可以用 SQL 重命名一张表或者一个字段的名称,这个名称就叫着该表或该字段的别名。
创建别名是为了让表名或列名的可读性更强。
SQL 中 使用 AS 来创建别名。
语法
表的别名语法:
SELECT column1, column2.... FROM table_name AS alias_name WHERE [condition];
列的别名语法:
SELECT column_name AS alias_name FROM table_name WHERE [condition];
实例
创建 COMPANY 表(下载 COMPANY SQL 文件 ),数据内容如下:
yssmxdb# select * from COMPANY; id_name _age_address _salary ----+-------+-----+-----------+-------- 1_Paul _ 32_California| 20000 2_Allen_ 25_Texas _ 15000 3_Teddy_ 23_Norway _ 20000 4_Mark _ 25_Rich-Mond_ 65000 5_David_ 27_Texas _ 85000 6_Kim _ 22_South-Hall| 45000 7_James_ 24_Houston _ 10000 (7 rows)
创建 DEPARTMENT 表(下载 COMPANY SQL 文件 ),数据内容如下:
yssmxdb=# SELECT * from DEPARTMENT; 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 (7 rows)
下面我们分别用 C 和 D 表示 COMPANY 表和 DEPAERMENT 表的别名:
yssmxdb=# SELECT C.ID, C.NAME, C.AGE, D.DEPT FROM COMPANY AS C, DEPARTMENT AS D WHERE C.ID = D.EMP_ID;
得到结果如下:
id_name _age_ dept ----+-------+-----+------------ 1_Paul _ 32_IT Billing 2_Allen_ 25_Engineering 7_James_ 24_Finance 3_Teddy_ 23_Engineering 4_Mark _ 25_Finance 5_David_ 27_Engineering 6_Kim _ 22_Finance (7 rows)
下面,我们用 COMPANY_ID 表示 ID 列,COMPANY_NAME 表示 NAME 列,来展示列别名的用法:
yssmxdb=# 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;
得到结果如下:
company_id_company_name_age_dept ------------+--------------+-----+------------ 1 _Paul _ 32_IT Billing 2 _Allen _ 25_Engineering 7 _James _ 24_Finance 3 _Teddy _ 23_Engineering 4 _Mark _ 25_Finance 5 _David _ 27_Engineering 6 _Kim _ 22_Finance (7 rows)