sql-server - 我们可以使用 Group by 子句执行像删除这样的 DML 操作吗？

Question

我们可以在 T-SQL 中使用 Group by 子句执行像删除这样的 DML 操作吗？

Answer 1

SELECT 语句 - http://msdn.microsoft.com/en-us/library/ms189499.aspx

DELETE 语句 - http://msdn.microsoft.com/en-us/library/ms189835.aspx

正如你所看到的，GROUP BY在SELECT中，但在DELETE中没有，所以你不能直接使用它。 INSERT 语句中也没有它。

[ WITH <common_table_expression> [ ,...n ] ]  
DELETE   
    [ TOP ( expression ) [ PERCENT ] ]   
    [ FROM ]   
    { <object> | rowset_function_limited   
      [ WITH ( <table_hint_limited> [ ...n ] ) ]  
    }  
    [ <OUTPUT Clause> ]  
    [ FROM <table_source> [ ,...n ] ]   
    [ WHERE { <search_condition>   
            | { [ CURRENT OF   
                   { { [ GLOBAL ] cursor_name }   
                       | cursor_variable_name   
                   }   
                ]  
              }  
            }   
    ]   
    [ OPTION ( <Query Hint> [ ,...n ] ) ]   
[; ]  

但是使用WHERE子句，或者子句，可以利用GROUP BY，比如

DELETE tbl
WHERE id NOT IN (select max(id) from tbl GROUP BY date_logged)

或

DELETE a
FROM tbl a
JOIN (select a_id from othertbl group by a_id having count(*) >= 3) b
    ON a.id = b.a_id