14、MySQL的计算字段

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1、字段的拼接 concat

select vend_name, vend_country, CONCAT(vend_name, '(', vend_country, ')') FROM vendors;

2、格式化相关字段 trim ltrim rtrim

select vend_name, vend_country, CONCAT(LTRIM(rtrim(vend_name)), '(', vend_country, ')') FROM vendors;

3、使用自动别名 as
4、数学计算

mysql> select prod_id, quantity * item_price as total from orderitems;
+---------+---------+
| prod_id | total   |
+---------+---------+
| ANV01   | 59.90   |
| ANV02   | 29.97   |
| TNT2    | 50.00   |
| FB      | 10.00   |
| JP2000  | 55.00   |
| TNT2    | 1000.00 |
| FC      | 125.00  |
| FB      | 10.00   |
| OL1     | 8.99    |
| SLING   | 4.49    |
| ANV03   | 14.99   |
+---------+---------+
11 rows in set (0.07 sec)