Question

我使用左外连接在SQL中加入了两个表（见下文）。

是否可以用其他数据填充空单元格？

（来自小提琴）

CREATE TABLE Data1
    (cost_type nvarchar(10), contract nvarchar(10))
;

INSERT INTO Data1
    (cost_type, contract)
VALUES
    ('LABR', 'contract1'),
    ('EQP', ''),
    ('RST', 'contract1')
;

CREATE TABLE data2
    (cost_type nvarchar(10), contract nvarchar(10), Name nvarchar(max))
;

INSERT INTO data2
    (cost_type,contract,Name)
VALUES
    ('LABR','contract1','John'),
    ('MAT','contract1','John'),
    ('EQP','','')
;

当前正在运行的查询：

select * from data1 dt1 
left outer join data2 dt2 on dt1.cost_type=dt2.cost_type

我需要的结果如下：

COST_TYPE  CONTRACT  NAME  
LABR, contract1, John  
EQP, contract1, John  
RST, contract1, John

此结果基于查找CONTRACT列的最常用值并使用该值替换所有空值。我需要为NAME列做同样的事情。

Answer 1

编辑：当您在上面的评论中明确表示您希望使用最常用的合同/名称填充的值时，查询并不是太复杂而无法编写; CTE用于查找每个最常用的合同/名称，以及用CTE值替换空值的查询;

WITH most_used_contract AS (
  SELECT TOP 1 contract FROM Data1
  WHERE contract IS NOT NULL
  GROUP BY contract
  ORDER BY COUNT(*) DESC
), most_used_name AS (
  SELECT TOP 1 name FROM Data2
  WHERE name IS NOT NULL
  GROUP BY name
  ORDER BY COUNT(*) DESC
)
SELECT data1.cost_type, 
       CASE WHEN data1.contract IS NULL OR data1.contract = ''
            THEN muc.contract
            ELSE data1.contract END contract, 
       CASE WHEN data2.name IS NULL OR data2.name = ''
            THEN mun.name
            ELSE data2.name END name
FROM data1  
LEFT JOIN data2 ON data1.cost_type=data2.cost_type
LEFT JOIN most_used_contract muc ON 1=1
LEFT JOIN most_used_name mun ON 1=1

An SQLfiddle to test with

SQl离开外连接以填充null

1 个答案: