Question

I’m trying to select all records that have a duplicate value in the LASTNAME column. This is my code so far

If EXISTS( SELECT name FROM sysobjects WHERE name = 'USER_DUPLICATES' AND type = 'U' ) 
    DROP TABLE USER_DUPLICATES
GO

CREATE TABLE USER_DUPLICATES
(
    FIRSTNAME VARCHAR(MAX),
    LASTNAME VARCHAR(MAX),
    PHONE VARCHAR(MAX),
    EMAIL VARCHAR(MAX),
    TITLE VARCHAR(MAX),
    LMU VARCHAR(MAX)
)
GO

INSERT INTO USER_DUPLICATES
(
    FIRSTNAME,
    LASTNAME,
    PHONE,
    EMAIL,
    TITLE,
    LMU
)
SELECT
    FIRSTNAME,
    LASTNAME,
    PHONE,
    EMAIL,
    TITLE,
    LMU
FROM TM_USER
GROUP BY
    FIRSTNAME,
    LASTNAME,
    PHONE,
    EMAIL,
    TITLE,
    LMU
HAVING COUNT(LASTNAME) > 1

It does not return any records. I changed the

HAVING COUNT(LASTNAME) > 1

to

HAVING COUNT(LASTNAME) > 0

and it returns all the records. I am also certain there are records with the same LASTNAME value. It is written using T-SQL on SQL Server

Answer 1

Try this:

SELECT
    a.FIRSTNAME,
    a.LASTNAME,
    a.PHONE,
    a.EMAIL,
    a.TITLE,
    a.LMU
FROM TM_USER a
INNER JOIN
(
    SELECT LASTNAME
    FROM TM_USER
    GROUP BY LASTNAME
    HAVING COUNT(1) > 1
) b ON a.LASTNAME = b.LASTNAME