The column in table 'Users' do not match an existing primary key or unique constraint

Question

I have two tables, 'Users' and 'IssueBooks'. In both the tables, I have ADMIN_ID,USN and E_ID as columns.

When I try to connect Users Table to IssueBooks Table making those columns foreign key, this error pops up:-

The column in table 'Users' do not match an existing primary key or unique constraint

All three columns are primary key and I want them to be foreign key in IssueBooks table.

All these columns are spelled same in both the tables.

Answer 1

It means that Users is having a combination not present in the parent table IssueBooks . Figure out the value and update it accordingly.

1. Figure out the combination, which is missing in parent

SELECT ADMIN_ID, USN, E_ID
FROM Users AS uo
WHERE NOT EXISTS (SELECT 1 FROM IssueBooks 
                  WHERE ADMIN_ID = uo.ADMIN_ID 
                    AND USN = uo.USN 
                    AND E_ID = uo.E_ID)

2. Now, you need to either update or delete the combination in Users :

UPDATE Users
SET ADMIN_ID = <newvalue>,
    USN = <newvalue>,
    E_ID = <newvalue>
WHERE ADMIN_ID = <oldvalue> 
  AND USN = <oldvalue> 
  AND E_ID = <oldvalue>

or

DELETE Users
WHERE ADMIN_ID = <oldvalue> AND USN = <oldvalue> AND E_ID = <oldvalue>

3. Now create the foreign key accordingly in Users table:

ALTER TABLE Users 
    ADD CONSTRAINT FK_Users_issueBooks 
        FOREIGN KEY (ADMIN_ID, USN, E_ID) 
        REFERENCES IssueBooks(ADMIN_ID, USN, E_ID)