如何比较where子句中的多行

Question

Given table:

create table borrower (
customer_number char ( 1 0 ) ,
loan_number char ( 1 0 ));

question: Find the customer number (ie, ID) of every customer that shares all of the loans that customer “1234” has. If the customer whose customer number is “1234” has loans “L1” and “L2”, you need to find all customers (including customer “1234”) that share both “L1” and “L2”.

I have created 4 entries in the table for the columns (customer_number, loan_number) are (1234, L1) (1234, L2) (1, LI)(1, L2)(2, L1). I am using query

select distinct customer_number 
from borrower
where loan_number IN(
    select loan_number 
    from borrower 
    where customer_number='1234'

but it is retrieving output such as

1234, 1, 2 

I want only 1 and 1234(Customer_number) in my output because it is the only one having both loan number L1 and L2. Cutsomer_number "2" is not associated with both the loan_number, so it should come in the out put.

I have also tried "all" in place of "IN".

select distinct customer_number 
    from borrower
    where loan_number= all(
        select loan_number 
        from borrower 
        where customer_number='1234'

output: nothing

Answer 1

Edit: As per OP's clarification

SELECT customer_number
FROM borrower b1
    WHERE b1.loan_number IN
    (SELECT loan_number FROM borrower
     WHERE customer_number=1234
     )
GROUP BY customer_number
HAVING count(*)=
  (SELECT count(*)
   FROM borrower
   WHERE customer_number=1234)

Explanation: First I am counting the number of loans for the given customer_number. In this case, it should be 2 . Now I am comparing this count with each group of customer_number where the count is same.

Answer 2

I think you want only customer_number who have both loan L1 and L2. so you try this code for your table

Query -

SELECT customer_number
FROM
  (SELECT customer_number,
          loan_number
   FROM borrower
   WHERE loan_number IN (SELECT loan_number FROM borrower
 WHERE customer_number=1234)
   GROUP BY loan_number,
            customer_number)t
GROUP BY customer_number
HAVING count(*) =
  (SELECT count(*)
   FROM borrower
   WHERE customer_number=1234)

If customer number not mentioned. But we need the customer list who are all applicable for all the loans like both L1 and L2

Query2 -

SELECT customer_number
FROM
  (SELECT customer_number,
          loan_number
   FROM borrower
   WHERE loan_number IN (SELECT distinct(loan_number) FROM borrower)
   GROUP BY loan_number,
            customer_number)t
GROUP BY customer_number
HAVING count(*) =
  (SELECT count(distinct(loan_number)) FROM borrower)

Explanation for Query2

SELECT distinct(loan_number) FROM borrower

loan_number
L1        
L2

The above query is used to find unique loans from borrower table.

SELECT customer_number, loan_number FROM borrower
   WHERE loan_number IN (SELECT loan_number FROM borrower
 WHERE customer_number=1234)
   GROUP BY loan_number, customer_number

customer_number    loan_number
1                   L1        
1234                L1        
2                   L1        
1                   L2        
1234                L2

This above query is used to find the customers who are all having the loans grouping based on their loans.

SELECT count(distinct(loan_number)) FROM borrower

The above code gives count 2 as output.(ie, L1 and L2). In Query Having count(*) will check how many times customer_number will present. From this example, it prints customer_number who are all presenting two times in table.

Finally Query2 shows the output like

1         
1234

Final output remove customer_number 2 because he has only "L1". Both user 1 and 1234 has both loans "L1" and "L2"

Hope this code will helps you.

Answer 3

Are you sure that you execute all the sql sentense? looks like its ok:

select distinct customer_number 
from borrower
where 
  loan_number IN(
    select a.loan_number from borrower a where a.customer_number='1234'
  )

Answer 4

You could use a temporary table and a join.

/* create a table of the loans we are looking for */
create table Temp select distinct loan_number from Borrower 
where customer_number = '1234';

/* join against the temp table and select borrowers with 3 matches */
select customer_number as 'Match' 
from (select customer_number, COUNT(*) as C 
         from Borrower 
         inner join Temp on Borrower.loan_number = Temp.loan_number
         group by customer_number) X
where C = 3

Answer 5

I got another query to retrieve desired rows, this query may not work in MySQL because of EXCEPT

Select customer_number from borrower as b
where not exists
   (select loan_number from borrower where customer_number='1234')
except
   (select loan_number from borrower where customer_number=b.customer_number)