MySQL 查询 WHERE -> IF

Question

希望有人能帮我解决这个问题，

我正在尝试将 MySQL 语句中的 WHERE 参数与 IF 操作连接起来，但我不知道如何处理它...

SELECT  k.EventId AS Id
    , ws.Name AS Name
    , dauer AS Dauer
    , kat.Name AS Kurztyp
    , doz.Name AS Dozent        
    , DATE_FORMAT(k.Begin, '%Y-%m-%d') AS Begin
    , COUNT(an.EventId) AS Teilnehmer
FROM kalender AS k
        LEFT JOIN workshop AS ws        
            ON (k.WorkshopId = ws.Id)
        LEFT JOIN angemeldet AS an      
            ON (k.EventId = an.EventId)
        LEFT JOIN dozent AS doz         
            ON (k.Dozent = doz.Id)
        LEFT JOIN ws_kategorie as kat   
            ON ((ws.Kategorie = kat.Id) or (ws.Kategorie2 = kat.Id))
        INNER JOIN bezahlvariante AS bezvar
                ON (an.bezahlvariante_idbezahlvariante = bezvar.idbezahlvariante)
    WHERE kat.Name LIKE '%security%'
        AND k.Begin > '2014-04-01'
        AND k.aktiv = '1'

---------------->

        AND bezvar.TN_Anzahl_phys = '1'

<---------------- 这应该是这样的:IF(COUNT(an.EventId)>0)
比 bezvar.TN_Anzahl_phys = '1'
ELSE bezvar.TN_Anzahl_phys IN (1,2)

            GROUP BY k.EventId;

如何在 MySQL 中使用这样的 IF 操作？

Answer 1

你可以使用case-when作为

GROUP BY k.EventId
having
case 
  when COUNT(an.EventId)>0 then bezvar.TN_Anzahl_phys = '1'
  else
   bezvar.TN_Anzahl_phys IN (1,2)
END