Question

有一个表“OBJECTS”，其中一列“OBJECT_NAME”具有三个值OBJ1，OBJ2，OBJ3。表OBJECTS的快照是：

OBJECT_NAME
----------
OBJ3
OBJ1
OBJ2
OBJ1
OBJ1
OBJ2

如何编写有效的SQL查询以获取输出格式的不同对象的计数，如下所示。

OBJ1_Count OBJ2_COUNT OBJ3_COUNT
--------------------------------- 
3              2           1

Answer 1

试试这个：

select
  sum(case when [object_name] = 'OBJ1' then 1 else 0 end) as obj1_count,
  sum(case when [object_name] = 'OBJ2' then 1 else 0 end) as obj2_count,
  sum(case when [object_name] = 'OBJ3' then 1 else 0 end) as obj3_count
from
  [objects]

object_name上的索引肯定是有益的

Answer 2

您可以使用数据透视表：

SELECT * FROM [OBJECTS] 
PIVOT (COUNT([OBJECT_NAME]) 
FOR [OBJECT_NAME] IN ([OBJ1],[OBJ2],[OBJ3])) AS [OBJCount]

如果您不想对列名进行硬编码，可以使用动态sql获取它们。

DECLARE @cols AS NVARCHAR(MAX)
,   @query AS NVARCHAR(MAX)

SET @cols = STUFF((SELECT DISTINCT
                            ',' + QUOTENAME(o.[OBJECT_NAME])
                   FROM     [OBJECTS] o
    FOR           XML PATH('')
                  ,   TYPE
            ).value('.', 'NVARCHAR(MAX)'), 1, 1, '')


SET @query = 'SELECT * FROM [OBJECTS] 
                PIVOT (COUNT([OBJECT_NAME]) 
                FOR [OBJECT_NAME] IN (' + @cols + ')) AS [OBJCount]'


EXECUTE(@query)

如何编写SQL查询以获取不同对象的计数

2 个答案: