SQL Server 2008 R2：在 VARCHAR 列上转换 table

Question

Table:

CREATE TABLE EMPDetails
(
    ID int,
    EmpName varchar(20),
    ColumnName varchar(20),
    ColumnValue varchar(20)
);

记录:

INSERT INTO EMPDetails Values(1,'S','Company','Microsoft');
INSERT INTO EMPDetails Values(1,'S','Profession','Database');
INSERT INTO EMPDetails Values(1,'S','Location','USA');
INSERT INTO EMPDetails Values(1,'S','Company','Unisys');
INSERT INTO EMPDetails Values(1,'S','Company','TATA');

INSERT INTO EMPDetails Values(2,'U','Company','Microsoft');
INSERT INTO EMPDetails Values(2,'U','Profession','Software');
INSERT INTO EMPDetails Values(2,'U','Location','UK');
INSERT INTO EMPDetails Values(2,'U','Company','DXC');
INSERT INTO EMPDetails Values(2,'U','Company','AOL');

INSERT INTO EMPDetails Values(3,'R','Company','Microsoft');
INSERT INTO EMPDetails Values(3,'R','Profession','Software');
INSERT INTO EMPDetails Values(3,'R','Location','UK');
INSERT INTO EMPDetails Values(3,'R','Company','AOL');

我的尝试

条件 1 : Company = 'Microsoft' AND Profession = 'Database'

预期结果：

ID  EmpName Company     Profession  Location
-----------------------------------------
1   S       Microsoft   Database    USA

查询：

SELECT *
FROM 
(
  SELECT ID, EmpName,ColumnValue, ColumnName
  FROM EMPDetails
) src
PIVOT
(
  MAX(ColumnValue) /*OR MIN()*/
  FOR ColumnName in ([Company], [Profession], [Location])
) piv
WHERE Company = 'Microsoft' AND Profession = 'Database'

条件 2 : Company = 'Microsoft' AND Profession = 'Software'

预期结果：

ID  EmpName Company     Profession  Location
-----------------------------------------
3   R       Microsoft   Software    UK
2   U       Microsoft   Software    UK

查询：

SELECT *
FROM 
(
  SELECT ID, EmpName,ColumnValue, ColumnName
  FROM EMPDetails
) src
PIVOT
(
  MAX(ColumnValue) /*OR MIN()*/
  FOR ColumnName in ([Company], [Profession], [Location])
) piv
WHERE Company = 'Microsoft' AND Profession = 'Software'

问题：如果我在条件 1 中使用 MIN() 聚合函数，则将得到结果，但在 MAX() 中不会得到结果，而在条件 2 中则相反。为什么？

Answer 1

您可以GROUP BY员工并在HAVING子句中使用条件计数，以获得满足条件的员工：

SELECT ID, EmpName      
FROM EMPDetails 
GROUP BY ID, EmpName
HAVING COUNT(CASE 
                WHEN ColumnName = 'Company' AND 
                     ColumnValue = 'Microsoft' THEN 1 
             END) > 0
       AND 
       COUNT(CASE 
                WHEN ColumnName = 'Profession' AND 
                ColumnValue = 'Database' THEN 1 
             END) > 0

以上查询选择 Microsoft 作为 Company 和 Database 作为 Profession 的员工。

输出：

ID  EmpName
------------
1   S

您现在可以使用条件聚合来透视员工行：

SELECT ID, EmpName,
       'Microsoft' AS Company,
       'Database' AS Profession,
       MAX(CASE WHEN ColumnName = 'Location' THEN ColumnValue END) AS Location
FROM EMPDetails 
GROUP BY ID, EmpName
HAVING COUNT(CASE 
                WHEN ColumnName = 'Company' AND 
                     ColumnValue = 'Microsoft' THEN 1 
             END) > 0
       AND 
       COUNT(CASE 
                WHEN ColumnName = 'Profession' AND 
                     ColumnValue = 'Database' THEN 1 
             END) > 0

不需要对Company或Profession值进行聚合，因为期望的值保证属于员工组。

输出：

ID  EmpName Company     Profession  Location
-----------------------------------------
1   S       Microsoft   Database    USA

要获得第二个结果集，只需将Database替换为Software:

SELECT ID, EmpName,
       'Microsoft' AS Company,
       'Software' AS Profession,
       MAX(CASE WHEN ColumnName = 'Location' THEN ColumnValue END) AS Location
FROM EMPDetails 
GROUP BY ID, EmpName
HAVING COUNT(CASE 
                WHEN ColumnName = 'Company' AND 
                     ColumnValue = 'Microsoft' THEN 1 
             END) > 0
       AND 
       COUNT(CASE 
                WHEN ColumnName = 'Profession' AND 
                     ColumnValue = 'Software' THEN 1 
             END) > 0

输出：

ID  EmpName Company     Profession  Location
---------------------------------------------
3   R       Microsoft   Software    UK
2   U       Microsoft   Software    UK

SQL Server 2008 R2：在 VARCHAR 列上转换 table

SQL Server 2008 R2: Pivot table on VARCHAR column

sql

pivot-table

sql-server-2008-r2