子查询以获取MAX值时出现错误消息

Question

我有以下选择语句：

SELECT
    l.rowno, 
    MAX(a.beac) AS AppBeacon,
    l.beac AS LoanBeacon
FROM 
    l
LEFT JOIN 
    a ON a.rowno = l.rowno
GROUP BY 
    l.rowno, l.beac
HAVING 
    rowno = l.rowno
ORDER BY
    l.rowno;

这将导致输出

我想做的是将AppBeacon和LoanBeacon合并为1列。我的标准是，如果LoanBeacon为<= 1，则只要AppBeacon不为null，就使用AppBeacon，否则使用LoanBeacon。

通过在这里查看其他问题，我尝试了一个子查询并提出了该查询

SELECT
    l.rowno,
    CASE
        WHEN l.beac <= 1 
           THEN (SELECT MAX(a.beac) 
                 FROM l
                 LEFT JOIN a ON a.rowno = l.rowno
                 GROUP BY rowno, loan.beacon
                 HAVING rowno = loan.rowno)
           ELSE loan.beacon
    END as BeaconFinal
FROM 
    l 
LEFT JOIN 
    a ON a.rowno = l.rowno
ORDER BY
    rowno;

这将导致此错误消息

  

子查询返回了多个值。当子查询遵循=，！=，<，<=，>，> =或将子查询用作表达式时，不允许这样做。

不太确定从这里去哪里，我们将不胜感激！

Answer 1

似乎应该可以...

select 
    rowno
    ,NewColumn = max(case when LoanBeacon <= 1 then coalesce(AppBeacon, LoanBeacon) else LoanBeacon end )
FROM 
    l
LEFT JOIN 
    a ON a.rowno = l.rowno
GROUP BY 
    l.rowno
ORDER BY
    l.rowno;

Answer 2

我认为这是您想要的逻辑：

HAVING

{{1}}子句没有做任何有用的事情，因此我将其删除。