Question

我想问一下如何制作这样的东西：

我有两个表格，我们称之为A和B。 A有一个amount_a，而B我们有amount_b。我想询问如何制作amount_a - amount_b，然后将结果设为amount_a。我该怎么做？所有简单的例子都很好看。非常感谢你

Answer 1

非常简单的示例（JOIN} id}：

CREATE两个包含五行数字的表格：

CREATE TABLE table_a (
   id int auto_increment primary key
 , amount_a int(2)
);

INSERT INTO table_a (amount_a)
VALUES (6),(72),(58),(39),(0);

CREATE TABLE table_b (
   id int auto_increment primary key
 , amount_b int(2)
);

INSERT INTO table_b (amount_b)
VALUES (1),(23),(31),(14),(51);

查询：

SELECT
   amount_a - amount_b AS amount
FROM table_a
JOIN table_b ON table_a.id = table_b.id

http://sqlfiddle.com/#!2/9b9c6/1

结果：

amount
5
49
27
25
-51

并运行UPDATE到amount_a：

UPDATE table_a
JOIN table_b ON table_a.id = table_b.id
SET amount_a = amount_a - amount_b

http://sqlfiddle.com/#!2/0c39e/1

Answer 2

您可以创建两个表并加入它们（可能在ID上）。然后从连接结果中选择amount_a - amount_b，如此SQL Fiddle http://sqlfiddle.com/#!2/f5334/4

所示

Sql问一下减去两个字段

2 个答案: