空值

Question

有我的代碼

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 

我要顯示在基於表的結構降低的結果，但結果是空值

Answer 1

@s需求是在MySQL中設置爲1 + NULL = NULL;您可以留下參加選擇設置變量在執行語句之前，如果你不能保持如下一個MySQL會話：

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