在mysql查询中创建和更新虚拟列值

Question

我的桌子结构是

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

问题：-

创建一个虚拟列(Column3)，该列具有启动值column3 = 0，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。

例如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

交叉连接应该解决这个问题：

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