sql - 缺少表的 FROM 子句条目

Question

我编写了以下 SQL 语句来从 gendata 和 TrainingMatrix 两个表中获取数据:

SELECT * FROM (SELECT DISTINCT ON ("TrainingMatrix".payroll, "TrainingName", "Institute")"gendata"."Employee Name","gendata"."Position", "gendata"."Department",  "TrainingMatrix".* 
FROM "TrainingMatrix" JOIN "gendata" ON "TrainingMatrix".payroll = "gendata".payroll 
ORDER  BY payroll, "TrainingName", "Institute" ,"TrainingDate" DESC NULLS LAST) AS foo;

它工作正常，但我需要通过以下方式更多地过滤记录:

WHERE "TrainingMatrix"."ExpiryDate" - current_date <= 0 
AND  EXTRACT(YEAR FROM  "TrainingMatrix"."ExpiryDate") = EXTRACT(YEAR FROM current_date);

因此，原始 SQL 语句将是:

SELECT * FROM (SELECT DISTINCT ON ("TrainingMatrix".payroll, "TrainingName", "Institute")"gendata"."Employee Name","gendata"."Position", "gendata"."Department",  "TrainingMatrix".* 
FROM "TrainingMatrix" JOIN "gendata" ON "TrainingMatrix".payroll = "gendata".payroll 
ORDER  BY payroll, "TrainingName", "Institute" ,"TrainingDate" DESC NULLS LAST) AS foo WHERE "TrainingMatrix"."ExpiryDate" - current_date <= 0 
AND  EXTRACT(YEAR FROM  "TrainingMatrix"."ExpiryDate") = EXTRACT(YEAR FROM current_date);

但是我得到了这个错误:

ERROR: missing FROM-clause entry for table "TrainingMatrix" LINE 3: ...te" ,"TrainingDate" DESC NULLS LAST) AS foo WHERE "TrainingM...

我正在使用 PostgreSQL。大家有什么建议吗？

Answer 1

100% 什么 @a_horse already said .加上更多的东西:

• 格式化您的查询，以便在您尝试调试之前易于阅读和理解。更重要的是，在您在公共(public)论坛上发帖之前。

• 使用 table aliases ，尤其是您不幸的 CaMeL 大小写名称，以使其更易于阅读。

• 在您的查询中提供您的表定义或至少 table-qualify 列名称，以便我们有机会对其进行解析。您的直接问题已在下面的查询中解决。您还可以相应地替换 ?.:

  • t .. “TrainingMatrix”
  的别名
  • g .. gendata
  的别名

SELECT *
FROM  (
    SELECT DISTINCT ON (t.payroll, ?."TrainingName", ?."Institute")
           g."Employee Name", g."Position", g."Department",  t.* 
    FROM   "TrainingMatrix" t
    JOIN   gendata          g  ON g.payroll = t.payroll 
    ORDER  BY t.payroll, ?."TrainingName", ?."Institute"
         , ?."TrainingDate" DESC NULLS LAST
    ) AS foo
WHERE  foo."ExpiryDate" - current_date <= 0 
AND    EXTRACT(YEAR FROM  foo."ExpiryDate") = EXTRACT(YEAR FROM current_date);

但还有更多。

• 如@a_horse 所写，使用必须一直用双引号引起来的非法标识符是个坏主意。但是 带有空格的标识符 字符更糟糕:“员工姓名”。这距离自制 SQL 注入(inject)仅一步之遥。

• 您的附加过滤器的措辞方式不利于性能。

  WHERE  "ExpiryDate" - current_date <= 0 
  

  不是sargable因此不能使用普通索引。撇开这一点不谈，它也比需要的更贵。改用:

  WHERE "ExpiryDate" >= current_date
  

  类似于您的第二个表达式，应将其重写为:

  WHERE  "ExpiryDate" >= date_trunc('year', current_date)
  AND    "ExpiryDate"  < date_trunc('year', current_date) + interval '1 year'
  

  结合两者，我们可以去除多余的表达式:

  WHERE  "ExpiryDate" >= current_date
  AND    "ExpiryDate"  < date_trunc('year', current_date) + interval '1 year'
  

• 您的问题不明确。您要在 DISTINCT 之前还是之后应用附加过滤器？不同的结果。
  假设 before DISTINCT，您不需要子查询 - 这消除了您当前问题的原因:子查询没有不同的别名。

一起:

SELECT DISTINCT ON (t.payroll, "TrainingName", "Institute") 
       g."Employee Name", g."Position", g."Department", t.* 
FROM   "TrainingMatrix" t
JOIN   gendata          g USING (payroll)
WHERE  t."ExpiryDate" >= current_date
AND    t."ExpiryDate" <  date_trunc('year', current_date) + interval '1 year'
ORDER  BY t.payroll, "TrainingName", "Institute", "TrainingDate" DESC NULLS LAST