How to delete records in the table which are repeated?

Question

Hi Here i came across a situation in which by mistakenly Without dropping the table i have run the batch file of the table which consists of some insert statements in detail

Answer 1

First , consider setting your ID fields as AI (auto increasment) and even PK (Primary Key).

In order to remove those duplicated rows , we will create a new table and will move all those duplicated rows to it. After that , drop that table.

CREATE TEMPORARY TABLE bad_temp AS SELECT DISTINCT * FROM alert_priority

Answer 2

you can copy all unique records into a new table, then delete the old table:

SELECT DISTINCT * INTO new_table FROM old_table

Answer 3

CREATE TABLE new_tbl(id int AUTO_INCREMENT,priority_name);

INSERT INTO new_tbl
select priority_name from old_tbl group by priority_name;

Answer 4

To just delete the duplicate new rows and leave the old ones in place (on the basis that I assume there are already other tables whose rows refer to the original rows):-

DELETE FROM alert_priority
WHERE Id IN (SELECT MaxId
FROM (SELECT priority_name, MAX(Id) AS MaxId, COUNT(Id)  AS CountId
FROM alert_priority
GROUP BY priority_name
HAVING CountId > 1))

Answer 5

Following query will give you all records that you want to keep:

SELECT min(id)
FROM alert_priority
GROUP BY priority_name
HAVING count(*) > 1
    OR min(id) = max(id)

To remove all duplicates, run this query:

DELETE FROM alert_priority
WHERE id NOT IN (
    SELECT min(id)
    FROM alert_priority
    GROUP BY priority_name
    HAVING count(*) > 1
        OR min(id) = max(id)
)

Answer 6

In SQL-Server it would be easy using ROW_NUMBER, but alas MySQL doesn't have a function like that :-(

Best way to solve it would be as follows:

• Create a new table identical in structure to the first, but with no data.
• Use the query: INSERT INTO name_of_new_table SELECT DISTINCT * FROM name_of_old_table
• Drop the old table
• Rename the new table to whatever the old table was called.