sql查询返回一行结果

Question

I am trying to write the query for existing table data. TABLE_A and TABLE_B has one record but TABLE_C has 2 records. One for Home address and other is for Work address.

So the following query returns 2 records. I am trying to get only one record out of 2 records.

If CITY is NULL, state_id is null for address_type = 1(Home) then get Work(address_type = 2) address. If both are null then get 'Home' address. What is the best way to achieve this functionality.

Thank you for any suggestion.

select a.A_ID, a.B_ID, a.A_DESC, b.first_name, b.last_name, c.address_type,  c.city, c.state
from table_A a
left join table_B b on b.B_ID = a.B_ID
left join table_C c on c.B_id = b.B_id
where a.A_ID = 10

TABLE_A

A_ID int
B_ID int 
A_Desc  varchar(20)

TABLE_B

B_ID int
first_name  varchar(30)
last_name   varchar(30)

TABLE_C

C_ID    int
B_ID    int 
address_type    int 
city      varchar(50)
state  int

Result:

 A_ID     B_ID   A_DESC   first_name  last_name  address_type   city       state
 --------------------------------------------------------------------------------
 10       200    test_     name1        name_last    1            NULL       NULL 
 10       200    test_     name1        name_last    2           City_test    2

I want this final result

 A_ID     B_ID   A_DESC   first_name  last_name  address_type   city       state
 --------------------------------------------------------------------------------
 10       200    test_     name1        name_last    2           City_test    2

Answer 1

You could use outer apply to look up the address with the highest type:

select  *
from    table_A a
left join 
        table_B b 
on      b.B_ID = a.B_ID
outer apply
        (
        select  top 1 *
        from    table_C c 
        where   c.B_id = b.B_id
        order by
                case
                when c.address_type = 2 and c.city is not null then 1
                else c.address_type = 1 and c.city is not null then 2
                end
        ) c
where   a.A_ID = 10

Answer 2

Just build this logic into your join condition for left joins to tables b and c.

If CITY is NULL, state_id is null for address_type = 1(Home) then get Work(address_type = 2) address. If both are null then get 'Home' address

Answer 3

select a.A_ID, a.B_ID, a.A_DESC, b.first_name, b.last_name,
       coalesce(c1.address_type,c2.address_type) address_type, 
       coalesce(c1.city,c2.city) city, 
       coalesce(c1.state,c2.state) state
from table_A a
left join table_B b on b.B_ID = a.B_ID
left join table_C c1 on c.B_id = b.B_id and c.Address_Type = 1
left join table_C c2 on c.B_id = b.B_id and c.Address_Type = 2

where a.A_ID = 10

Answer 4

the general technique:

select distinct a.A_ID
, a.B_ID
, a.A_DESC
, b.first_name
, b.last_name
, coalesce(home.address_type, work.address_type)
, coalesce(home.city,work.city)
, coalesce(home.state, work.state) 
from table_A a 
left join table_B b on b.B_ID = a.B_ID 
left join table_C home on home.B_id = b.B_id and home.address_type = 1
left join table_C work on work.B_id = b.B_id and home.address_type = 2
where a.A_ID = 10