我需要知道如何创建交叉表查询

我想动态生成状态列。

有三张表，资产、资产类型、资产状态

Table: assets
assetid     int
assettag    varchar(25)
assettype   int
assetstatus int

Table: assettypes
id         int
typename   varchar(20)  (ex: Desktop, Laptop, Server, etc.)

Table: assetstatus
id         int
statusname varchar(20)  (ex: Deployed, Inventory, Shipped, etc.)
  

期望的结果：

AssetType     Total   Deployed   Inventory  Shipped     ...
-----------------------------------------------------------
Desktop         100       75        20          5       ...
Laptop           75       56        19          1       ...
Server           60       50        10          0       ...

一些数据：

assets table:
1,hol1234,1,1
2,hol1233,1,2
3,hol3421,2,3
4,svr1234,3,1

assettypes table:
1,Desktop
2,Laptop
3,Server

assetstatus table:
1,Deployed
2,Inventory
3,Shipped
  

这种类型的转换称为枢轴。您没有指定您使用的数据库，因此我将提供 SQL Server 和 MySQL 的答案。

SQL服务器：如果您使用的是 SQL Server 2005+，您可以实施PIVOT功能。

如果您有已知数量的想要转换为列的值，那么您可以对查询进行硬编码。

select typename, total, Deployed, Inventory, shipped
from
(
  select count(*) over(partition by t.typename) total,
    s.statusname,
    t.typename
  from assets a
  inner join assettypes t
    on a.assettype = t.id
  inner join assetstatus s
    on a.assetstatus = s.id
) d
pivot
(
  count(statusname)
  for statusname in (Deployed, Inventory, shipped)
) piv;

See SQL 摆弄演示 http://www.sqlfiddle.com/#!3/d7915/5.

但如果你有未知数量的status值，那么您将需要使用动态 sql 在运行时生成列列表。

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

select @cols = STUFF((SELECT distinct ',' + QUOTENAME(statusname) 
                    from assetstatus
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'')

set @query = 'SELECT typename, total,' + @cols + ' from 
             (
                select count(*) over(partition by t.typename) total,
                  s.statusname,
                  t.typename
                from assets a
                inner join assettypes t
                  on a.assettype = t.id
                inner join assetstatus s
                  on a.assetstatus = s.id
            ) x
            pivot 
            (
                count(statusname)
                for statusname in (' + @cols + ')
            ) p '

execute(@query)

See SQL 摆弄演示 http://www.sqlfiddle.com/#!3/d7915/7

这也可以使用带有 case 表达式的聚合函数来编写：

select typename,
  total,
  sum(case when statusname ='Deployed' then 1 else 0 end) Deployed,
  sum(case when statusname ='Inventory' then 1 else 0 end) Inventory,
  sum(case when statusname ='Shipped' then 1 else 0 end) Shipped
from
(
  select count(*) over(partition by t.typename) total,
    s.statusname,
    t.typename
  from assets a
  inner join assettypes t
    on a.assettype = t.id
  inner join assetstatus s
    on a.assetstatus = s.id
) d
group by typename, total

See SQL 摆弄演示 http://www.sqlfiddle.com/#!3/d7915/10

MySQL:该数据库没有pivot函数，因此您必须使用聚合函数和CASE表达。它也没有窗口函数，因此您必须将查询稍微更改为以下内容：

select typename,
  total,
  sum(case when statusname ='Deployed' then 1 else 0 end) Deployed,
  sum(case when statusname ='Inventory' then 1 else 0 end) Inventory,
  sum(case when statusname ='Shipped' then 1 else 0 end) Shipped
from
(
  select t.typename,
    (select count(*) 
     from assets a1 
     where a1.assettype = t.id 
     group by a1.assettype) total,
    s.statusname
  from assets a
  inner join assettypes t
    on a.assettype = t.id
  inner join assetstatus s
    on a.assetstatus = s.id
) d
group by typename, total;

See SQL 摆弄演示 http://www.sqlfiddle.com/#!2/9f4cd/7

那么如果你需要 MySQL 中的动态解决方案，则必须使用准备好的语句来生成要执行的 sql 字符串：

SET @sql = NULL;
SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'sum(CASE WHEN statusname = ''',
      statusname,
      ''' THEN 1 else 0 END) AS `',
      statusname, '`'
    )
  ) INTO @sql
FROM assetstatus;

SET @sql 
  = CONCAT('SELECT typename,
              total, ', @sql, ' 
            from
            (
              select t.typename,
                (select count(*) 
                 from assets a1 
                 where a1.assettype = t.id 
                 group by a1.assettype) total,
                s.statusname
              from assets a
              inner join assettypes t
                on a.assettype = t.id
              inner join assetstatus s
                on a.assetstatus = s.id
            ) d
            group by typename, total');

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

See SQL 摆弄演示 http://www.sqlfiddle.com/#!2/9f4cd/6.

两个数据库中的所有查询的结果相同：

| TYPENAME | TOTAL | DEPLOYED | INVENTORY | SHIPPED |
-----------------------------------------------------
|  Desktop |     2 |        1 |         1 |       0 |
|   Laptop |     1 |        0 |         0 |       1 |
|   Server |     1 |        1 |         0 |       0 |