MYSQL中遇到的问题以及解决方法（三）横转纵

横转纵直接就用case when ,对于数值类的可以添加个聚合函数，那么文本类的也可以添加聚合函数吗？

select PatientID ,  Age, Sex, Height, Weight,OperatorID,BMI,
max(case when rank%2=1 then KRKPPGFilePath else '' end) KRKPPGFilePath , 
max(case when rank%2=1 then SBP else '' end) SBP,
max(case when rank%2=1 then DBP else '' end) DBP,
max(case when rank%2=0 then KRKPPGFilePath else '' end) KRKPPGFilePath1 , 
max(case when rank%2=0 then SBP else '' end) SBP1,
max(case when rank%2=0 then DBP else '' end) DBP1 from (
select PatientID , KRKPPGFilePath, SBP, DBP, Age, Sex, Height, Weight,round(BMI,2)BMI,OperatorID,rank from (select a.*,IF (@p=PatientID,@r:=@r+1,@r:=1) as rank,@p:=PatientID from (select     p.PatientID , p.KRKPPGFilePath, p.SBP, p.DBP, pa.Age, pa.Sex, pa.Height, pa.Weight,pa.BMI,p.OperatorID
FROM
    ppg_data AS p
    LEFT JOIN 
    (select *,pa.Weight/power(pa.Height,2)*10000 as BMI from patient AS pa)pa ON p.PatientID=pa.PatientID 
    LEFT JOIN operator AS o ON o.OperatorID = p.OperatorID
    where p.PatientID in (
    select PatientID from (    SELECT
    p.PatientID , count(0)
FROM
    ppg_data AS p
    LEFT JOIN 
    (select *,pa.Weight/power(pa.Height,2)*10000 as BMI from patient AS pa)pa ON p.PatientID=pa.PatientID
    LEFT JOIN operator AS o ON o.OperatorID = p.OperatorID
WHERE
    p.TestEndTime >= '2019-12-17 00:00:01' 
    AND p.TestEndTime < '2020-07-08 00:00:01' 
    AND p.State = '1' 
    AND pa.Age>=16
    AND pa.Age<=120
    AND pa.Weight>=30
    AND pa.Weight<=160
    AND pa.Height>=130
    AND pa.Height<=220
    AND p.SBP>p.DBP
    AND BMI>=15
    AND BMI<=50
    AND pa.RecordIsDeleted = 0
    AND o.isCensus = 1
     and p.Quality=1
    AND p.KRKPPGFilePath IS NOT NULL 
    AND p.SBP IS NOT NULL
    group by p.PatientID
    having count(0)=1 )A)
    and p.TestEndTime >= '2019-12-17 00:00:01' 
    AND p.TestEndTime < '2020-07-08 00:00:01' 
    AND p.State = '1' 
  and p.Quality=1
    AND pa.Age>=16
    AND pa.Age<=120
    AND pa.Weight>=30
    AND pa.Weight<=160
    AND pa.Height>=130
    AND pa.Height<=220
    AND p.SBP>p.DBP
    AND BMI>=15
    AND BMI<=50
    AND pa.RecordIsDeleted = 0
    AND o.isCensus = 1
    AND  p.KRKPPGFilePath IS NOT NULL
    AND p.SBP IS NOT NULL
ORDER BY p.PatientID)a,(select @p:=NUll,@r:=0)r)a
where rank<3)A
group by  PatientID ,  Age, Sex, Height, Weight,BMI

文本类的数据也是可以添加聚合函数的，PPGFilePath是一推数字和字母组合在一起的，和NULL取最大仍然也是可以取出来的。