Question

我有两个如上所示的表格。我想创建一个选择语句，其结果如下：

基本上，我想加入“ Model”和“ Num”列，并引入“ Val”值，但基于“ Ver”将其分为两列。


SELECT 'a' as Model ,'1' as Num ,'v1' as Ver ,'9' as val INTO #RefTbl UNION ALL
SELECT 'a','2','v1','10' UNION ALL
SELECT 'a','3','v1','11' UNION ALL
SELECT 'a','1','v2','5' UNION ALL
SELECT 'a','2','v2','6' UNION ALL
SELECT 'a','3','v2','7' UNION ALL
SELECT 'b','1','v1','20' UNION ALL
SELECT 'b','1','v2','21' UNION ALL
SELECT 'b','2','v1','25' UNION ALL
SELECT 'b','2','v2','26'


SELECT '519' as ID,'a' as Model,'1' as Num INTO #OrderTbl UNION ALL
SELECT '5616','a','3' UNION ALL
SELECT '871','b','1' 


-- failed attempt
SELECT o.*, '' as v1_val, '' as v2_val FROM #OrderTbl as o left join #RefTbl as r on o.Model = r.Model and o.Num = r.Num

Answer 1

您可以加入并进行条件聚合：

select
    d.ID,
    d.Model,
    d.Num,
    max(case when r.Ver = 'val1' then Val end) V1_Val,
    max(case when r.Ver = 'val2' then Val end) V2_Val
from DataTbl d
inner join ReferenceTbl r 
    on  r.Model = d.Model
    and r.Num = d.Num
group by
    d.ID,
    d.Model,
    d.Num

或者，您可以加入两次-根据您的数据集，这可能会（或可能不会）表现更好：

select
    d.ID,
    d.Model,
    d.Num,
    r1.Val V1_Val,
    r2.Val V2_Val
from DataTbl d
left join ReferenceTbl r1 
    on  r1.Model = d.Model
    and r1.Num = d.Num
    and r1.Ver = 'val1'
left join ReferenceTbl r2
    on  r2.Model = d.Model
    and r2.Num = d.Num
    and r2.Ver = 'val2'

Answer 2

Case + Group by可在大多数数据库系统上使用，这很好。

使用SQL Server PIVOT的替代答案（供参考）

WITH RefTbl AS (
    SELECT 'a' as Model ,'1' as Num ,'v1' as Ver ,'9' as val UNION ALL
    SELECT 'a','2','v1','10' UNION ALL
    SELECT 'a','3','v1','11' UNION ALL
    SELECT 'a','1','v2','5' UNION ALL
    SELECT 'a','2','v2','6' UNION ALL
    SELECT 'a','3','v2','7' UNION ALL
    SELECT 'b','1','v1','20' UNION ALL
    SELECT 'b','1','v2','21' UNION ALL
    SELECT 'b','2','v1','25' UNION ALL
    SELECT 'b','2','v2','26'), 
OrderTbl AS (
    SELECT '519' as ID,'a' as Model,'1' as Num UNION ALL
    SELECT '5616','a','3' UNION ALL
    SELECT '871','b','1' 
)
SELECT Id, Model, Num AS Model, [v1] AS v1_Val, [v2] as v2_Val
FROM  
    (SELECT o.id, r.Model, r.Num, r.val, r.ver from OrderTbl as o 
     left join RefTbl as r on o.Model = r.Model and o.Num = r.Num) AS SourceTable  
PIVOT  
(MAX(val) FOR ver IN ([v1], [v2])) AS PivotTable;

Id      Model   Model   v1_Val  v2_Val
519     a       1       9       5
5616    a       3       11      7
871     b       1       20      21

SQL连接，并将1列分为2列

2 个答案: