枢轴/逆透视表

Question

我需要改造如下的数据：

EmployeeId  DataCategory  DataValue  StartDate 
----------  ------------  ---------- ---------- 
    2   'OfficeCode'   121  '03-01-12' 
    2   'ManagerName'  'Steven'  '02-04-12' 
    2   'State'    'MA'  '04-05-12' 
    5   'OfficeCode'   133  '04-01-12' 
    5   'ManagerName'  'Marcus'  '05-04-12' 
    5   'State'    'WA'  '01-05-12' 
    6   'ManagerName'  'Steven'  '07-04-12' 
    6   'State'    'RI'  '06-05-12' 
    7   'State'    'CA'  '08-08-12' 

到：

EmployeeId  OfficeCode  ManagerName State  OfficeCodeStartDate 
----------  ------------  ---------- ---------- ------------------- 
    2    121   'Steven'  'MA'   '03-01-12' 
    5    133   'Marcus'  'WA'   '04-01-12' 
    6    null   'Steven'  'RI'   null 
    7    null   null   'CA'   null 

我能够枢转这样的：

select EmployeeId, OfficeCode, ManagerName, State 
from 
(
    select EmployeeId, DataCategory, DataValue 
    from emp 
) src 
pivot 
(
    max(DataValue) 
    for DataCategory in (OfficeCode, ManagerName, State) 
) piv 

然而，我还需要DataCategory OfficeCode的StartDate（忽略任何其他类别的开始日期）。你能帮我用pivot/unpivot实现想要的结果吗？除非需要，我试图避免联合/联合。

Answer 1

三种方式：一种是UNION，一种是JOIN，一种是没有PIVOT。选择一个你最喜欢的（根据查询计划，最后一个是最快的）。

/* 
CREATE TABLE emp (
    EmployeeId INT, 
    DataCategory VARCHAR(50), 
    PRIMARY KEY (EmployeeID, DataCategory), 
    DataValue VARCHAR(50) NOT NULL, 
    StartDate VARCHAR(10) NOT NULL 
) 

INSERT INTO emp VALUES 
('2','OfficeCode','121','03-01-12'), 
('2','ManagerName','Steven','02-04-12'), 
('2','State','MA','04-05-12'), 
('5','OfficeCode','133','04-01-12'), 
('5','ManagerName','Marcus','05-04-12'), 
('5','State','WA','01-05-12'), 
('6','ManagerName','Steven','07-04-12'), 
('6','State','RI','06-05-12'), 
('7','State','CA','08-08-12') 
*/ 

select EmployeeId, OfficeCode, ManagerName, State, OfficeCodeStartDate 
from 
(
    select EmployeeId, DataCategory, DataValue 
    from emp 
    union all 
    select EmployeeId, 'OfficeCodeStartDate' AS DataCategory, StartDate AS DataValue 
    from emp 
    WHERE DataCategory='OfficeCode' 
) src 
pivot 
(
    max(DataValue) 
    for DataCategory in (OfficeCode, ManagerName, State, OfficeCodeStartDate) 
) piv 

select piv.EmployeeId, OfficeCode, ManagerName, State, emp.StartDate AS OfficeCodeStartDate 
from 
(
    select EmployeeId, DataCategory, DataValue 
    from emp 
) src 
pivot 
(
    max(DataValue) 
    for DataCategory in (OfficeCode, ManagerName, State) 
) piv 
LEFT JOIN emp ON emp.EmployeeId=piv.EmployeeId AND emp.DataCategory='OfficeCode' 

SELECT EmployeeId, 
    MIN(CASE WHEN DataCategory='OfficeCode' THEN DataValue END) AS OfficeCode, 
    MIN(CASE WHEN DataCategory='ManagerName' THEN DataValue END) AS ManagerName, 
    MIN(CASE WHEN DataCategory='State' THEN DataValue END) AS State, 
    MIN(CASE WHEN DataCategory='OfficeCode' THEN StartDate END) AS OfficeCodeStartDate 
FROM emp 
GROUP BY EmployeeId