sql - oracle sql 选择语法与 GROUP BY 和 HAVING 子句

Question

我一直在通过一些 sql 语法来学习 oracle sql 考试，我发现一些相当困惑的东西

基于 official引用，选择语法如下:

SELECT
    [ hint ]
    [ { { DISTINCT | UNIQUE } | ALL } ]
   select_list
     FROM { table_reference | join_clause | ( join_clause ) }
            [ , { table_reference | join_clause | (join_clause) } ] ...
     [ where_clause ]
     [ hierarchical_query_clause ]
     [ group_by_clause ]
     [ HAVING condition ]
     [ model_clause ]

基于此，您不能在 GROUP BY 子句之前使用 HAVING 子句。但是，如果我要在测试服务器中执行以下 sql:

select 
   department_id , count (*)      
from 
    employees 
having 
    count(*) > 6 
group by 
    department_id ; 

它不会产生语法错误，有人可以帮忙解释一下吗？我不喜欢认为引用文档是错误的，但如果是这样，我需要一些确认。

Answer 1

如前所述 here :

Use the HAVING clause to restrict the groups of returned rows to those groups for which the specified condition is TRUE. If you omit this clause, then the database returns summary rows for all groups.

Specify GROUP BY and HAVING after the where_clause and hierarchical_query_clause. If you specify both GROUP BY and HAVING, then they can appear in either order.