如何在 WHERE 子句上使用选择（查询）别名？

Question

我的查询有问题，这是工作查询，

    SELECT res_ID,res_fName,res_mName,res_lName,rs.suffix,rms.marital_Name,rg.gender_Name,rr.religion_Name,ro.occupation_Name,ros.occuStat_Name,res_Date_Record,rc.country_citizenship,res_Bday,TIMESTAMPDIFF(YEAR,res_Bday,CURDATE()) AS age,
(case  
 when (TIMESTAMPDIFF(Month,res_Bday,CURDATE())<=1) then 'Maternal and Newborn'
 when (TIMESTAMPDIFF(Month,res_Bday,CURDATE())<=1 and TIMESTAMPDIFF(Month,res_Bday,CURDATE())<=12) then 'Babies'
when (TIMESTAMPDIFF(Month,res_Bday,CURDATE())<=13 and TIMESTAMPDIFF(Month,res_Bday,CURDATE())<=24) then 'Toddlers'
when (TIMESTAMPDIFF(Year,res_Bday,CURDATE())<=2 and TIMESTAMPDIFF(Year,res_Bday,CURDATE())<=4) then 'Preschoolers'
 when (TIMESTAMPDIFF(Year,res_Bday,CURDATE())<=5 and TIMESTAMPDIFF(Year,res_Bday,CURDATE())<=8) then 'School Age Children'
 when (TIMESTAMPDIFF(Year,res_Bday,CURDATE())<=9 and TIMESTAMPDIFF(Year,res_Bday,CURDATE())<=12) then 'Tweens '
when (TIMESTAMPDIFF(Year,res_Bday,CURDATE())<=13 and TIMESTAMPDIFF(Year,res_Bday,CURDATE())<=19) then 'Teenager'
when (TIMESTAMPDIFF(Year,res_Bday,CURDATE())<=20 and TIMESTAMPDIFF(Year,res_Bday,CURDATE())<=35) then 'Young Adult'
when (TIMESTAMPDIFF(Year,res_Bday,CURDATE())<=36 and TIMESTAMPDIFF(Year,res_Bday,CURDATE())<=55) then 'Middle-Aged Adults'
when (TIMESTAMPDIFF(Year,res_Bday,CURDATE())<=56 and TIMESTAMPDIFF(Year,res_Bday,CURDATE())<=100) then 'Senior'
   end) Age_Stage
FROM resident_detail rd 
LEFT JOIN ref_suffixname rs ON rd.suffix_ID = rs.suffix_ID 
LEFT JOIN ref_gender rg ON rd.gender_ID = rg.gender_ID
LEFT JOIN ref_marital_status rms ON rms.marital_ID = rd.marital_ID
LEFT JOIN ref_religion rr ON rr.religion_ID = rd.religion_ID 
LEFT JOIN ref_occupation ro ON ro.occupation_ID = rd.occupation_ID 
LEFT JOIN ref_occupation_status ros ON ros.occuStat_ID = rd.occuStat_ID
LEFT JOIN ref_country rc ON rc.country_ID = rd.country_ID

这是结果：

我想要在 WHERE 语句中使用别名“Age_Stage”列，在上面的图像上 Age_Stage 有它们的特定值，我只想按我想要的值过滤那些 Age_Stage。但是当我在查询WHERE Age_Stage = "Young Adult"上添加 查询时，错误是结果是

“where 子句”中的未知列“Age_Stage”

Answer 1

重命名发生在 WHERE 之后。您可以重复以下CASE语句：

SELECT res_ID,res_fName,res ...
   (case ... end) as Age_Stage
FROM resident_detail rd
LEFT JOIN ...
WHERE (case ... end) = 'Young Adult'

或嵌套语句：

SELECT ...
FROM (
    SELECT res_ID,res_fName,res ...
       (case ... end) as Age_Stage
    FROM resident_detail rd
    LEFT JOIN ...
) AS T
WHERE Age_Stage = 'Young Adult'

或者您可以尝试将其添加到 HAVING 子句中。正如 ypercube 所指出的那样？？在评论中，MySQL 通过在重命名之前评估 HAVING (... as Age_Stage) 来偏离标准。这是一个在以下情况下似乎非常常用于 MySQL 的技巧：

SELECT res_ID,res_fName,res ...
   (case ... end) as Age_Stage
FROM resident_detail rd
LEFT JOIN ...
HAVING Age_Stage = 'Young Adult'