从2个不相关的表中选择并合并唯一的ID列

Question

I'm trying to return a combined result of data from 2 tables, but need to merge the ID column from both to form one result set, the full outer join is the closest I have to returning the correct row number.

Example:

T1

ID  A
a   s
b   s
e   s
f   s

T2

ID  B
a   a
c   a
d   a
f   a

Result

ID   A      B
a    s      a
b    s      NULL
c    NULL   a
d    NULL   a
e    s      NULL
f    s      a



    declare @t1 table (
                  ID varchar(1),
                  A varchar(1)
                 )
insert into @t1 values ('a','s')
insert into @t1 values ('b','s')
insert into @t1 values ('e','s')
insert into @t1 values ('f','s')

declare @t2 table (
                  ID varchar(1),
                  B varchar(1)
                 )

insert into @t2 values ('a','a')
insert into @t2 values ('c','a')
insert into @t2 values ('d','a')
insert into @t2 values ('f','a')

select * from @t1
select * from @t2

Answer 1

If you are using MySQL; you don't have FULL JOINS in MySQL, but you can surely emulate them .

For a code SAMPLE transcribed from this SO question you have:

with two tables t1, t2:

SELECT * FROM t1
LEFT JOIN t2 ON t1.id = t2.id
UNION
SELECT * FROM t1
RIGHT JOIN t2 ON t1.id = t2.id

So your query becomes:

SELECT COALESCE(t1.ID, t2.ID) As ID, t1.A As A, t2.B As B FROM table1 t1
LEFT JOIN table2 t2 ON t1.id = t2.id
UNION
SELECT COALESCE(t1.ID, t2.ID) As ID, t1.A As A, t2.B As B FROM table1 t1
RIGHT JOIN table2 t2 ON t1.id = t2.id
order by ID

It gives me correct result with your inputs as:

ID   A      B
a    s      a
b    s      NULL
c    NULL   a
d    NULL   a
e    s      NULL
f    s      a