综合练习： PIVOTUNPIVOTGROUPING SETSGROUPING_ID_1

Posted 2020-12-09 cdpj

综合练习： PIVOT、UNPIVOT、GROUPING SETS、GROUPING_ID

/*
    《Microsoft SQL Server 2008 T-SQL Fundamentals》
*/
------------------------------------------------------------------
select *
from Orders
------------------------------------------------------------------
--按照empid分组
select empid
from Orders
group by empid
------------------------------------------------------------------
--按YY分组
select datepart(yy,orderdate)
from Orders
group by datepart(yy,orderdate)
------------------------------------------------------------------

------------------------------------------------------------------
--按empid, orderid,YY分组
select empid, orderid, datepart(yy,orderdate),
           count(*)
from Orders
group by empid, orderid, datepart(yy,orderdate)
------------------------------------------------------------------
----按empid, YY分组
select empid,  datepart(yy,orderdate) as YY,
           count(*) as cnt
from Orders
group by empid,  datepart(yy,orderdate)
------------------------------------------------------------------
----按empid, YY分组
select empid,  YEAR(orderdate) as YY    --, count(*) as cnt
from Orders
------------------------------------------------------------------
        --从上面这个步骤，直接得出最后的结果，交叉时之前的子查询不要分组，统计，   还是多熟悉一下pivot，unpivot的语法
        select empid, [2007], [2008], [2009]
        from (                          
                    select empid,  datepart(yy,orderdate) as YY
                    from Orders
                ) as d
            pivot(count(YY) for YY in([2007], [2008], [2009])) as p    --对于交叉时，一直不想在这里用列举的方法，假使这里的值很多时？
------------------------------------------------------------------
            ----按empid, YY分组，不需要的思考过程，就向后缩进
            --select empid, -- datepart(yy,orderdate),
            --           (case when datepart(yy,orderdate)=‘2007‘ then count(*) end) AS cnt2007,
            --           (case when datepart(yy,orderdate)=‘2008‘ then count(*) end) AS cnt2008,
            --           (case when datepart(yy,orderdate)=‘2009‘ then count(*) end) AS cnt2009
            --from Orders
            --group by empid,  datepart(yy,orderdate)
------------------------------------------------------------------
----按empid，这就是最后的结果，虽然是最后的结果，是以订单数量的次数在相加
select empid, -- datepart(yy,orderdate),
          count(case when datepart(yy,orderdate)=‘2007‘ then qty end) AS cnt2007,
          count(case when datepart(yy,orderdate)=‘2008‘ then qty end) AS cnt2008,
          count(case when datepart(yy,orderdate)=‘2009‘ then qty end) AS cnt2009
from Orders
group by empid
------------------------------------------------------------------
----按empid，这就是最后的结果，以出现的 “年” 相同的次数在相加
select empid, -- datepart(yy,orderdate),
          count(case when year(orderdate)=‘2007‘ then year(orderdate) end) AS cnt2007,
          count(case when year(orderdate)=‘2008‘ then year(orderdate) end) AS cnt2008,
          count(case when year(orderdate)=‘2009‘ then year(orderdate) end) AS cnt2009
from Orders
group by empid
------------------------------------------------------------------
--将查询的结果集，插入到另外一个表中去，目的是什么？ ---看这么查询得出这么整齐的结果，当然是想训练UNPIVOT
IF OBJECT_ID(‘dbo.EmpYearOrders‘, ‘U‘) IS NOT NULL DROP TABLE dbo.EmpYearOrders;

SELECT empid, [2007] AS cnt2007, [2008] AS cnt2008, [2009] AS cnt2009
INTO dbo.EmpYearOrders
FROM (SELECT empid, YEAR(orderdate) AS orderyear
      FROM dbo.Orders) AS D
  PIVOT(COUNT(orderyear)
        FOR orderyear IN([2007], [2008], [2009])) AS P;

SELECT * FROM dbo.EmpYearOrders;
    empid       cnt2007     cnt2008     cnt2009
    ----------- ----------- ----------- -----------
     1           1           1          1
     2           1           2          1
     3           2           0          2
------------------------------------------------------------------
--将上面这个结果，转化为下面的，打散开
empid       orderyear   numorders
----------- ----------- -----------
1           2007        1
1           2008        1
1           2009        1
2           2007        1
2           2008        2
2           2009        1
3           2007        2
3           2009        2

SELECT empid, orderyear, numorders
FROM dbo.EmpYearOrders
  UNPIVOT(numorders 
                   for orderyear in(cnt2007, cnt2008,cnt2009)) AS U
where numorders <> 0
------------------------------------------------------------------

------------------------------------------------------------------
--
--select * from Orders
select grouping(empid) as groupingset, empid, custid, year(orderdate) as orderyear, sum(qty) as sumqty
from Orders
group by
    grouping sets(
                            (empid, custid, year(orderdate)),
                            (empid,  year(orderdate)),
                            (custid, year(orderdate))      --如果分组包含()，则结果集中将会计算总的数量（sumqty = 205)
                         )
------------------------------------------------------------------
-- Write a query against the Orders table that returns the total quantities for each: 
-- (employee, customer, and order year), (employee and order year), (customer and order year). 
-- Include a result column in the output that uniquely identifies the grouping set with which the current row is associated. 
-- 用GROUPING_ID函数为与每一行相关联的分组集生成唯一的标识符
select grouping_id(empid,custid,year(orderdate)) as groupingset, empid, custid, year(orderdate) as orderyear, sum(qty) as sumqty
from Orders
group by
    grouping sets(
                   (empid, custid, year(orderdate)),
                   (empid,  year(orderdate)),
                   (custid, year(orderdate))                        
                 )

 感悟：也许国内出书都是以结果为导向，或者为升职、或者为名，反正出的书、或者翻译的书籍，即使自己懂、理解、或没完全理解透彻，翻译出来的书籍都不是那么理想的，
            并不是在否定他们的劳动成果，你出书，面向哪个级别的书籍，就应该针对哪个级别要进行理解性的讲解。