您可以通过Alias 在表或列上起一个别名,表别名的使用是在特定的SQL语句中重命名表,列别名用于重命名表的列,以用于特定的SQL查询。
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];
请考虑以下两个表。
表1 -客户表(CUSTOMERS)如下。
+----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Learnfk | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+
表2 -订单表(ORDERS)如下。
+-----+---------------------+-------------+--------+ |OID | DATE | CUSTOMER_ID | AMOUNT | +-----+---------------------+-------------+--------+ | 102 | 2019-10-08 00:00:00 | 3 | 3000 | | 100 | 2019-10-08 00:00:00 | 3 | 1500 | | 101 | 2019-11-20 00:00:00 | 2 | 1560 | | 103 | 2018-05-20 00:00:00 | 4 | 2060 | +-----+---------------------+-------------+--------+
现在,以下代码块显示了表别名的用法。
SQL> SELECT C.ID, C.NAME, C.AGE, O.AMOUNT FROM CUSTOMERS AS C, ORDERS AS O WHERE C.ID=O.CUSTOMER_ID;
这将产生以下输出。
链接:https://www.learnfk.comhttps://www.learnfk.com/sql/sql-alias-syntax.html
来源:LearnFk无涯教程网
+----+----------+-----+--------+ | ID | NAME | AGE | AMOUNT | +----+----------+-----+--------+ | 3 | kaushik | 23 | 3000 | | 3 | kaushik | 23 | 1500 | | 2 | Khilan | 25 | 1560 | | 4 | Chaitali | 25 | 2060 | +----+----------+-----+--------+
以下是列别名的用法。
SQL> SELECT ID AS CUSTOMER_ID, NAME AS CUSTOMER_NAME FROM CUSTOMERS WHERE SALARY IS NOT NULL;
这将产生以下输出。
链接:https://www.learnfk.comhttps://www.learnfk.com/sql/sql-alias-syntax.html
来源:LearnFk无涯教程网
+-------------+---------------+ | CUSTOMER_ID | CUSTOMER_NAME | +-------------+---------------+ | 1 | Ramesh | | 2 | Khilan | | 3 | kaushik | | 4 | Chaitali | | 5 | Hardik | | 6 | Komal | | 7 | Learnfk | +-------------+---------------+
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