Question

我有以下加入查询。

select
  SD.id,
  SD.Scenario,
  PR.Type,
  PR.StationName,
  max(if(PARAM='minH',Value,' ')) as 'Min H',
  max(if(PARAM='maxQ',Value,' ')) as 'Max Q',
  max(if(PARAM='avQ',Value,' ')) as 'AV Q',
  dsd.Dam_Min_Level,
  dsd.Dam_Max_Level
from sgwebdb.param_reference as PR
  Inner join sgwebdb.scenario_data as SD
    ON PR.Param_Id = SD.Param_Id
  INNER JOIN sgwebdb.qualicision_detail as Q
    ON SD.SCENARIO = Q.Alternative
  INNER JOIN sgwebdb.dam_station_detail as dsd
    ON dsd.Station_Id = PR.Station_Id
where PR.Type = 'Reservoirs'
    and Q.Alternative = 'C'
GROUP BY PR.Id;

，输出低于

ID   Scenario     Type      StationName  Min H  Max Q   AV Q   Dam_Min_Level   Dam_Max_Level
3   C   Reservoirs  Beris   82.1461            23            33
7   C   Reservoirs  Muda    90.6169            4.8           4.4
11  C   Reservoirs  Beris       1.49           23            33
15  C   Reservoirs  Muda        0          4.8           4.4
19  C   Reservoirs  Pedu            36.262     23            33

如何用0号代替Min H，Max Q和AV Q列的空白单元格。

Answer 1

你可以这样做

select
  SD.id,
  SD.Scenario,
  PR.Type,
  PR.StationName,
  max(if(PARAM='minH',Value,0)) as 'Min H',
  max(if(PARAM='maxQ',Value,0)) as 'Max Q',
  max(if(PARAM='avQ',Value,0)) as 'AV Q',
  dsd.Dam_Min_Level,
  dsd.Dam_Max_Level
from sgwebdb.param_reference as PR
  Inner join sgwebdb.scenario_data as SD
    ON PR.Param_Id = SD.Param_Id
  INNER JOIN sgwebdb.qualicision_detail as Q
    ON SD.SCENARIO = Q.Alternative
  INNER JOIN sgwebdb.dam_station_detail as dsd
    ON dsd.Station_Id = PR.Station_Id
where PR.Type = 'Reservoirs'
    and Q.Alternative = 'C'
GROUP BY PR.Id;

你唯一需要做的就是将{0}作为IF条件中的第二个参数而不是空字符串

连接查询中的默认空值

1 个答案: