Question

我的表结构是

customer  column1 column2(int) 
  1        sale      2            
  1        return    1            
  1        sale      3             
  1        sale      1             
  1        return    1

问题： -

创建一个具有起始值`column3 = 0`的虚拟列（column3），并根据`column1`和`column2`值更新其值。我找不到一起创建和更新虚拟列的查询。

e.g。 IF(column1='sale',column3 + column2, column3-column2 )

// start value of column3 = 0 for each product
customer  column1 column2(int) column3
  1        sale      2             2  //0+2 because it is a sale 
  1        return    1             1  //2-1 because it is a return 
  1        sale      3             4  //1+3 because it is a sale 
  1        sale      1             6  //4+2 because it is a sale 
  1        return     1            4  //6-2 because it is a return

Answer 1

CROSS JOIN应该解决这个问题：

SELECT
    t.column1,
    t.column2,
    CASE
WHEN t.column1 = 'sale' THEN
    @id :=@id + t.column2
ELSE
    @id :=@id - t.column2
END AS column3
FROM
(SELECT @id:=0) var
CROSS JOIN table1 t

在mysql查询中创建和更新虚拟列值

1 个答案: