mysql - 数学 mySQL 的空值

Question

这是我的代码

select @k:=if(kode="k",nominal,0) as Kredit,@d:=if(kode="d",nominal,0) as
 debet, @s:=@s+@k-@d as saldo from trx

我想根据表的结构显示归约结果，但结果是空值

Answer 1

@s需要在MySQL中设置为1 + NULL = NULL；如果您无法维护 MySQL session ，您可以在执行语句之前保留 join 选择来设置变量，如下所示:

SELECT 
    @k := IF(kode = "k", nominal, 0) AS Kredit, 
    @d := IF(kode = "d", nominal, 0) as debet, 
    @s:= @s + @k - @d AS saldo 
FROM trx 
    LEFT JOIN (SELECT @s := 0) AS `setVar` ON 1=1