Question

我想弄清楚哪种方式更有效率。我试图使用Sql Fiddle，但它似乎没有认识到PIVOT或UNION 我可以查看哪些工具或统计数据来确定哪个更有效。

CREATE TABLE T
(
  PersonNum INT
 ,WeekOf DATETIME
 ,ActivityType1 INT
 ,ActivityType2 INT
 ,Hours INT
)

INSERT INTO T VALUES(1,'11/2/2014',5,0,40)
INSERT INTO T VALUES(1,'11/2/2014',1,0,5)
INSERT INTO T VALUES(1,'11/2/2014',1,0,8)
INSERT INTO T VALUES(1,'11/2/2014',2,1,6)
INSERT INTO T VALUES(1,'11/2/2014',2,2,2)
INSERT INTO T VALUES(1,'11/2/2014',2,3,9)
INSERT INTO T VALUES(1,'11/2/2014',2,4,7)

INSERT INTO T VALUES(1,'11/9/2014',5,0,40)
INSERT INTO T VALUES(1,'11/9/2014',1,0,2)
INSERT INTO T VALUES(1,'11/9/2014',1,0,6)
INSERT INTO T VALUES(1,'11/9/2014',2,1,7)
INSERT INTO T VALUES(1,'11/9/2014',2,2,2)
INSERT INTO T VALUES(1,'11/9/2014',2,3,3)
INSERT INTO T VALUES(1,'11/9/2014',2,4,5)

方法1

SELECT 
  PersonNum
, WeekOf
, SUM(CASE WHEN ActivityType1 = 5 THEN Hours ELSE 0 END) AS Beginning
, SUM(CASE WHEN ActivityType1 = 1 THEN Hours ELSE 0 END) AS Plus
, SUM(CASE WHEN ActivityType1 = 2 AND ActivityType2 <> 3 THEN Hours ELSE 0 END) AS Minus
, SUM(CASE WHEN ActivityType1 = 2 AND ActivityType2 = 3 THEN Hours ELSE 0 END) AS MinusSpecial
FROM T
GROUP BY 
  PersonNum
, WeekOf

方法2

SELECT
  PersonNum
, WeekOf
, [Beginning]
, [Plus]
, [Minus]
, [Minus Special]
FROM
(
  SELECT
    PersonNum
  , WeekOf
  , 'Beginning' AS ColumnType
  , Hours
  FROM T
  WHERE
    ActivityType1 = 5 
  UNION
  SELECT
    PersonNum
  , WeekOf
  , 'Plus' AS ColumnType
  , Hours
  FROM T
  WHERE
    ActivityType1 = 1 
  UNION
  SELECT
    PersonNum
  , WeekOf
  , 'Minus' AS ColumnType
  , Hours
  FROM T
  WHERE
      ActivityType1 = 2 
  AND ActivityType2 <> 3
   UNION
  SELECT
    PersonNum
  , WeekOf
  , 'Minus Special' AS ColumnType
  , Hours
  FROM T
  WHERE
      ActivityType1 = 2 
  AND ActivityType2 = 3
    ) Data  
PIVOT 
(SUM(Hours)
FOR ColumnType IN ([Beginning]                
                  ,[Plus]
                  ,[Minus]
                  ,[Minus Special])
) pvt

Answer 1

我可以建议重写你的PIVOT查询，这样你就不必再敲5次了。

select P.PersonNum,
       P.WeekOf,
       P.Beginning,
       P.Plus,
       P.Minus,
       P.MinusSpecial
from (
     select T.PersonNum,
            T.WeekOf,
            T.Hours,
            case ActivityType1 
             when 5 then 'Beginning'  
             when 1 then 'Plus'
             when 2 then case ActivityType2
                           when 3 then 'MinusSpecial'
                           else 'Minus'
                         end
            end as ColumnType
     from T
     ) as T
pivot (sum(T.Hours) for T.ColumnType in (Beginning, Plus, MinusSpecial, Minus)) as P

通过查询，您可能会获得与您的组相同的查询计划，并且性能相同。

Answer 2

你可以这样做

set statistics time on

--first query

set statistics time off

set statistics time on

--second query

set statistics time off

您可以在“消息”窗口中查看执行时间

Answer 3

方法1肯定会更快。这是因为只有一个select语句。另一方面，方法2中有5个select语句。一般规则是查询包含的语句越多，执行时间就越长。

Pivot vs Case T-sql效率

3 个答案: