选择联合SQL

Question

I am using the following query :

select 8 Union Select 0 Union Select 15 

to populate the these 3 number in a column. The result I get is:

0  
8  
15

But I want 8 to come first and then 0 and then 15, eg

8  
0  
15

How do I do this?

Answer 1

使用UNION ALL Eg

select 8 UNION ALL Select 0 UNION ALL Select 15 

Answer 2

@SimonMartin's answer works for the exact data set you give, but be aware that if your data set contains duplicate values, the UNION ALL will produce different results than UNION .

The UNION operator removes duplicates, whereas the UNION ALL will preserve them (as well as their order, as noted in @SimonMartin's answer).

If you want to combine the functionality of your UNION operator with the ordering capabilities provided by UNION ALL , then you need to start with UNION ALL then filter out the duplicate values yourself:

-- baseline query + 1 duplicate record at the end
with query as 
(
    select 8 as Val
        UNION ALL 
    Select 0 as Val
        UNION ALL 
    Select 15 as Val
        UNION ALL 
    Select 0 as Val
)
-- now add row numbers
, queryWithRowNumbers as 
(
    select row_number() over (order by (select 0)) as rn, Val
    from query
)
-- finally, get rid of the duplicates
select Val from (
    select Val, min(rn) as minRn
    from querywithrownumbers
    group by val
) q
order by minRn

This will give results of

8
0
15

whereas if you ONLY use UNION ALL you will end up with

8
0
15
0