sql - Mysql 内部查询不工作

Question

    $sql= "select 
            tblservergroup.id,
            tblservergroup.groupname,

            if(tblservergroup.defserverpaid='0', '0', select concat(tblservers.ipaddress, ' (', tblservers.name, ')' ) as defaultserverpaiddesc from tblservers where tblservers.id=tblservergroup.defserverpaid),
            if(tblservergroup.defserverfree='0', '0', select concat(tblservers.ipaddress, ' (', tblservers.name, ')' ) as defaultserverfreedesc from tblservers where tblservers.id=tblservergroup.defserverfree),      

            tblservergroup.note
            from tblservergroup
";

这个类似的概念可以在MSSQL中完成，但是当我在mysql中编写它时，它显示错误。帮助。

Answer 1

如果你坚持使用子查询，你可以这样做:

SELECT
    tblservergroup.id,
    tblservergroup.groupname,
    tblservergroup.note,
    IF(defserverpaid='0', '0', (SELECT concat(ipaddress, ' (', name, ')') FROM tblservers WHERE id=defserverpaid)) AS defaultserverpaiddesc,
    IF(defserverfree='0', '0', (SELECT concat(ipaddress, ' (', name, ')') FROM tblservers WHERE id=defserverfree)) AS defaultserverfreedesc
FROM
    tblservergroup

我建议改用LEFT JOIN:

SELECT
    tblservergroup.id,
    tblservergroup.groupname,
    tblservergroup.note,
    IF(defserverpaid='0', '0', concat(ts1.ipaddress, ' (', ts1.name, ')')) as defaultserverpaiddesc
    IF(defserverfree='0', '0', concat(ts2.ipaddress, ' (', ts2.name, ')')) as defaultserverfreedesc
FROM
    tblservergroup
    LEFT JOIN tblservers ts1 ON ts1.id=defserverpaid
    LEFT JOIN tblservers ts2 ON ts2.id=defserverfree

理想情况下，还可以在 defserverpaid/defserverfree 中存储 NULL 而不是 0，并添加外键约束。