Postgres SQL - 列不存在

Question

SELECT nmemail as order_email, 
       dtorder, 
       vlOrder, 
       cohorts.cohortdate 
FROM   factorderline 
       JOIN (SELECT nmemail as cohort_email, Min(dtorder) AS cohortDate FROM  factorderline GROUP  BY cohort_email limit 5) cohorts 
ON order_email= cohort_email limit 5;

ERROR: column "order_email" does not exist

这个查询有什么问题？

Answer 1

问题很可能是在评估联接时尚未解析列别名的定义；请改用实际的列名：

SELECT nmemail as order_email, 
       dtorder, 
       vlOrder, 
       cohorts.cohortdate 
FROM   factorderline 
JOIN (
  SELECT nmemail as cohort_email, Min(dtorder) AS cohortDate 
  FROM  factorderline 
  GROUP BY cohort_email limit 5
) cohorts ON nmemail = cohort_email 
limit 5;

此外，在使用 limit 时，您确实应该使用 order by 子句。

来自文档：

When using LIMIT, it is important to use an ORDER BY clause that constrains the result rows into a unique order. Otherwise you will get an unpredictable subset of the query's rows.

Answer 2

问题是输出列名称不能用于联接。

来自the documentation：

An output column's name can be used to refer to the column's value in ORDER BY and GROUP BY clauses, but not in the WHERE or HAVING clauses; there you must write out the expression instead.

Postgres SQL - 列不存在

Postgres SQL - Column does not exist

sql

postgresql

column-alias