如果在联合中未找到任何行，请选择一些默认值

Question

我正在尝试做这样的事情，其中​​不存在ID = 2的行

SELECT 
     coalesce( ID, 1 ) as ID 
     , coalesce( someVal, 0 ) as someVal
     FROM tablename WHERE ID = 1
UNION ALL
SELECT 
     coalesce( ID, 2 ) as ID 
     , coalesce( someVal, 0 ) as someVal
     FROM tablename WHERE ID = 2
UNION ALL
SELECT 
     coalesce( ID, 3 ) as ID 
     , coalesce( someVal, 0 ) as someVal
     FROM tablename WHERE ID = 3

我得到的是

ID   |    someVal
1    |    500.23
3    |    492.01

我想要的是

ID   |    someVal
1    |    500.23
2    |    0
3    |    492.01

如果没有相应ID的记录，如何使它返回带有一些默认值的行？

Answer 1

我相信您想在两个不同的选择中选择两个列

 SELECT ISNULL((SELECT isnull( ID, 2 ) FROM #tablename WHERE ID = 2),2) ,
 ISNULL((SELECT isnull( someval, 2 ) FROM #tablename WHERE ID = 2),0)

码：

create table #tablename (id int ,someval int)

insert into  #tablename values (1,500)

insert into  #tablename values (3,492.23)

 SELECT ISNULL((SELECT isnull( ID, 1 ) FROM #tablename WHERE ID = 1),2) ,
 ISNULL((SELECT isnull( someval, 0 ) FROM #tablename WHERE ID = 1),0)
 union all
 SELECT ISNULL((SELECT isnull( ID, 2 ) FROM #tablename WHERE ID = 2),2) ,
 ISNULL((SELECT isnull( someval, 0 ) FROM #tablename WHERE ID = 2),0)
 union all
 SELECT ISNULL((SELECT isnull( ID, 3 ) FROM #tablename WHERE ID = 3),2) ,
 ISNULL((SELECT isnull( someval, 0 ) FROM #tablename WHERE ID = 3),0)

Answer 2

您需要具有带有ID值的数字表，并将LEFT JOIN与原始表一起使用，如下所示。 根据您的需要，数字表也可以是临时表。

DECLARE @tbl table(ID INT IDENTITY, SomeVal INT) 
INSERT INTO @tbl VALUES
(1)  
,(2)
,(3); 

DECLARE @numtbl TABLE(ID INT);
INSERT INTO @numtbl VALUES
(1)  
,(2)
,(3)
,(4) -- not present in original table
,(5); --not present in original table

SELECT (t.ID) as id, COALESCE(t1.SomeVal,0)  as someval
FROM
@numtbl AS t 
LEFT JOIN @tbl AS t1
ON t.ID = t1.ID 
WHERE t.ID = 5 -- ID is not present in original table