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mysqlsqljoinmysql5
Lalith B
Lalith B

Reputation: 12239

MySQL Query Join to select unmatched rows from two tables

I have two tables as below.

user_id   |   username        |  first_name |   role_type
-----------------------------------------------------------
1         |   testuser1       |  testu1     |    student
2         |   testuser2       |  testu2     |    student
3         |   testuser3       |  testu3     |    student
4         |   testuser4       |  testu4     |    student
5         |   testuser5       |  testu5     |    student
6         |   testuser6       |  testu6     |    admin
7         |   testuser7       |  testu7     |    admin
-----------------------------------------------------------

user_id   |   username         |    approved_id
----------------------------------------------------------------------
1         |   testuser1        |  3B888F52-50BC-11E2-B08B-99E5B2CADDF7
2         |   testuser2        |  3B888F52-50BC-11E2-B08B-99E5B2CADDF7
3         |   testuser3        |  3B888F52-50BC-11E2-B08B-99E5B2CADDF7
----------------------------------------------------------------------

I tried the query 

SELECT users.* FROM users 
WHERE users.username NOT IN(
     SELECT users_approval.username FROM users_approval 
     WHERE users_approval.approved_id = "3B888F52-50BC-11E2-B08B-99E5B2CADDF7"
) AND users.role_type = "student"

and got the result below 

user_id   |   username        |  first_name |   role_type
-------------------------------------------------------------
4         |   testuser4       |  testu4     |    student
5         |   testuser5       |  testu5     |    student
-------------------------------------------------------------

Is there any way to use JOIN to fetch the same resultset as above ?.

Help is much appriciated.

Upvotes: 2

Views: 11336

Answers (2)

Muhammad Raheel
Muhammad Raheel

Reputation: 19882

SELECT 
    users.* 
FROM users as u
LEFT JOIN users_approval as ua ON  ua.id = u.id
WHERE u.role_type = "student" AND ua.approved_id IS NULL

Assuming you have user_id as foreign key in the second table it can be used to join instead of using username to join table

Upvotes: 2

John Woo
John Woo

Reputation: 263693

SELECT users.* 
FROM   users 
       LEFT JOIN users_approval b
          ON users.username = b.username AND
             b.approved_id = "3B888F52-50BC-11E2-B08B-99E5B2CADDF7"
WHERE  users.role_type = "student" AND
       b.approved_id IS NULL

Upvotes: 10

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