How to delete from select in MySQL?

问题

This code doesn't work for MySQL 5.0, how to re-write it to make it work

DELETE FROM posts where id=(SELECT id FROM posts GROUP BY id  HAVING ( COUNT(id) > 1 ))

I want to delete columns that dont have unique id. I will add that most of the time its only one id(I tried the in syntax and it doesnt work as well).

回答1:

SELECT (sub)queries return result sets. So you need to use IN, not = in your WHERE clause.

Additionally, as shown in this answer you cannot modify the same table from a subquery within the same query. However, you can either SELECT then DELETE in separate queries, or nest another subquery and alias the inner subquery result (looks rather hacky, though):

DELETE FROM posts WHERE id IN (
    SELECT * FROM (
        SELECT id FROM posts GROUP BY id HAVING ( COUNT(id) > 1 )
    ) AS p
)

Or use joins as suggested by Mchl.

回答2:

DELETE 
  p1
  FROM posts AS p1 
CROSS JOIN (
  SELECT ID FROM posts GROUP BY id HAVING COUNT(id) > 1
) AS p2
USING (id)

回答3:

you can use inner join :

DELETE 
    ps 
FROM 
    posts ps INNER JOIN 
         (SELECT 
           distinct id 
         FROM 
             posts 
         GROUP BY id  
      HAVING COUNT(id) > 1 ) dubids on dubids.id = ps.id

回答4:

If you want to delete all duplicates, but one out of each set of duplicates, this is one solution:

DELETE posts
FROM posts
LEFT JOIN (
    SELECT id
    FROM posts
    GROUP BY id
    HAVING COUNT(id) = 1

    UNION

    SELECT id
    FROM posts
    GROUP BY id
    HAVING COUNT(id) != 1
) AS duplicate USING (id)
WHERE duplicate.id IS NULL;

来源：https://stackoverflow.com/questions/4562787/how-to-delete-from-select-in-mysql

标签

sql

mysql

select

uniqueidentifier

subquery