I need an update statement to resolve some issues with duplicates in a table on MySQL. The table structure is shown below. I need a MySQL statement that will set the value of duplicate as NULL except the first one, i.e the one with the lowest id. Here the id is the primary key.
This is an example of what I have:
id name
1 foo
2 foo
3 bar
4 NULL
5 NULL
6 foo
7 bar
This is the desired result:
id name
1 foo
2 NULL
3 bar
4 NULL
5 NULL
6 NULL
7 NULL
The table has other columns with useful information. Hence, the row can't just simply be deleted.
I would write this as:
UPDATE t JOIN
(SELECT name, MIN(id) as min_id
FROM t
GROUP BY name
) tt
ON t.name = tt.name and t.id > tt.min_id
SET t.name = NULL;
I think the logic is easier to follow using JOIN. Basically, it says to find the minimum id for each name. Then set all other rows for the same name to NULL.
Your UPDATE query can include a JOIN.
e.g. join the minimum id for each name and only update where the id is not the minimum.
UPDATE
t
LEFT OUTER JOIN (
SELECT
MIN(id) AS id
FROM
t
GROUP BY
name
) t1 ON t.id = t1.id
SET
t.name = NULL
WHERE
t1.id IS NULL
DB Fiddle
UPDATE t JOIN
(SELECT name, MIN(id) as min_id
FROM t
WHERE name IS NOT NULL
GROUP BY name
HAVING COUNT(*) > 1
) tt
ON t.name = tt.name and t.id > tt.min_id
SET t.name = NULL;
I wasn't sure how to word the title, but here is what I am trying to do. I have a table where the id can have multiple entries
id | number
___________
1 | 90
1 | 88
2 | 88
3 | 88
I want a query that will return all ids that don't contain the number 90, so only 2 and 3 in this example. I have tried the below, but it still returns the id of 1 since it also has a number of 88.
SELECT DISTINCT id FROM table WHERE number NOT IN (90)
One way of getting the result is by using NOT EXISTS. Basically what it does it it gets all ID which has 90 in the inner query and the NOT EXISTS only shows all ID not in the inner query.
SELECT A.*
FROM TableName a
WHERE NOT EXISTS (SELECT NULL
FROM TableName B
WHERE a.ID = b.ID
AND b.number = 90)
Here's a Demo.
An alternative is by using LEFT JOIN which yields the same result as above.
SELECT a.*
FROM TableName a
LEFT JOIN TableName b
ON a.ID = b.ID
AND b.number = 90
WHERE b.id IS NULL
Here's a Demo.
You can use subquery:
SELECT id
FROM table
WHERE id NOT IN (SELECT id FROM table WHERE number = 90)
You can use aggregation as illustrated below for better performance:
SELECT ID
FROM YourTable
GROUP BY ID
HAVING NOT INSTR(GROUP_CONCAT(`number`),'90');
Demo on SQL Fiddle.
I have a database table with the columns: email, name, id
There are duplicate records with the same email and name (ids may or may not be different)
I want to remove all duplicates and not keep any of them.
Example
email | name | id
-------------------------------------------------
a#b.com | a | 2 --- remove
a#b.com | a | 4 --- remove
b#c.com | b | 3
c#d.com | c | 5
What sql query can I use in phpmyadmin to do this?
You could use EXISTS:
DELETE FROM TableName t1
WHERE EXISTS
(
SELECT 1 FROM TableName t2
WHERE t1.id <> t2.id
AND COALESCE(t1.email,'') = COALESCE(t2.email,'')
AND COALESCE(t1.name,'') = COALESCE(t2.name,'')
)
I've used COALESCE to also delete duplicates if the emails or names are null.
In MySQL, you should do this with a join:
delete t
from example t join
(select email, name
from example
group by email, name
having count(*) > 1
) todelete
on t.email = todelete.email and t.name = todelete.name;
Unfortunately, MySQL does not support simple subqueries on the table being modified in an update or delete statement.
EDIT:
Deleting a lot of records can be a performance bottleneck. To get around this, create a temporary table with the records you want, truncate the original table, and re-insert them.
So, try this:
create temporary table tempt as
select t.*
from example t join
(select email, name
from example
group by email, name
having count(*) = 1
) tokeep
on t.email = tokeep.email and t.name = tokeep.name;
truncate table example;
insert into example
select * from tempt;
Try the select query first to be sure it has reasonable performance and does what you want.
DELETE n1 FROM tablename n1, tablename n2 WHERE n1.email = n2.email
I am using MySQL 5.6.17.
I have a self-referencing table TableA with columns id (PK), title (varchar), type (varchar), parent_id (FK that refers to id of the same table).
The sample data is as below :
id title type parent_id
1 abc G NULL
2 def G NULL
3 xyz G NULL
4 pqr G NULL
5 abc T NULL
6 def T NULL
7 xyz T NULL
8 pqr T NULL
Now, I want each record having type='G' should become the child of the record with type='T' having the same title.
So the resultant table data should be :
id title type parent_id
1 abc G 5
2 def G 6
3 xyz G 7
4 pqr G 8
5 abc T NULL
6 def T NULL
7 xyz T NULL
8 pqr T NULL
I've tried query below :
UPDATE TableA
SET parent_id = (SELECT id FROM ( SELECT id FROM TableA WHERE TYPE='T' ) d)
WHERE TYPE='G';
But it returns
Error Code: 1242
Subquery returns more than 1 row
I also have tried :
UPDATE TableA t1
SET t1.parent_id = t2.newlocalid
INNER JOIN (
SELECT title, id AS newlocalid
FROM TableA t2
WHERE TYPE='T'
) t2 ON t1.title = t2.title
WHERE t1.type='G'
But it also returns the error in Syntax.
Can anyone help me to achieve it?
UPDATE TABLEA a
JOIN TABLEA b ON a.title = b.title and a.type='G'and b.type='T'
SET a.parent_id = b.id
This should work:
SELECT title, id AS newlocalid
INTO #t2
FROM TableA
WHERE TYPE='T'
UPDATE t1
SET t1.parent_id = t2.newlocalid
FROM TableA as t1
INNER JOIN #t2 as t2
ON t1.title = t2.title
WHERE t1.type='G'
Try:
UPDATE TableA a
SET parent_id = (SELECT id FROM TableA ref WHERE TYPE='T' AND ref.title=a.title)
WHERE TYPE='G';
to update the table column first you have to identify which value to set. you can not use multiple values to update the single column in same statement.
change your sql to something like this:
UPDATE TableA
SET parent_id = (SELECT id FROM TableA WHERE TYPE='T' limit 0,1)// i mean make sure that it is returning single record not multiple.or better add some more where condition to get a single and required record without using limit
WHERE TYPE='G';
or to some specific condition like this:
UPDATE TableA
SET parent_id = (SELECT id FROM TableA aa WHERE TYPE='T' and aa.type=TableA.type)
WHERE TYPE='G';
I want to pull out duplicate records in a MySQL Database. This can be done with:
SELECT address, count(id) as cnt FROM list
GROUP BY address HAVING cnt > 1
Which results in:
100 MAIN ST 2
I would like to pull it so that it shows each row that is a duplicate. Something like:
JIM JONES 100 MAIN ST
JOHN SMITH 100 MAIN ST
Any thoughts on how this can be done? I'm trying to avoid doing the first one then looking up the duplicates with a second query in the code.
The key is to rewrite this query so that it can be used as a subquery.
SELECT firstname,
lastname,
list.address
FROM list
INNER JOIN (SELECT address
FROM list
GROUP BY address
HAVING COUNT(id) > 1) dup
ON list.address = dup.address;
SELECT date FROM logs group by date having count(*) >= 2
Why not just INNER JOIN the table with itself?
SELECT a.firstname, a.lastname, a.address
FROM list a
INNER JOIN list b ON a.address = b.address
WHERE a.id <> b.id
A DISTINCT is needed if the address could exist more than two times.
I tried the best answer chosen for this question, but it confused me somewhat. I actually needed that just on a single field from my table. The following example from this link worked out very well for me:
SELECT COUNT(*) c,title FROM `data` GROUP BY title HAVING c > 1;
Isn't this easier :
SELECT *
FROM tc_tariff_groups
GROUP BY group_id
HAVING COUNT(group_id) >1
?
select `cityname` from `codcities` group by `cityname` having count(*)>=2
This is the similar query you have asked for and its 200% working and easy too.
Enjoy!!!
Find duplicate users by email address with this query...
SELECT users.name, users.uid, users.mail, from_unixtime(created)
FROM users
INNER JOIN (
SELECT mail
FROM users
GROUP BY mail
HAVING count(mail) > 1
) dupes ON users.mail = dupes.mail
ORDER BY users.mail;
we can found the duplicates depends on more then one fields also.For those cases you can use below format.
SELECT COUNT(*), column1, column2
FROM tablename
GROUP BY column1, column2
HAVING COUNT(*)>1;
Finding duplicate addresses is much more complex than it seems, especially if you require accuracy. A MySQL query is not enough in this case...
I work at SmartyStreets, where we do address validation and de-duplication and other stuff, and I've seen a lot of diverse challenges with similar problems.
There are several third-party services which will flag duplicates in a list for you. Doing this solely with a MySQL subquery will not account for differences in address formats and standards. The USPS (for US address) has certain guidelines to make these standard, but only a handful of vendors are certified to perform such operations.
So, I would recommend the best answer for you is to export the table into a CSV file, for instance, and submit it to a capable list processor. One such is LiveAddress which will have it done for you in a few seconds to a few minutes automatically. It will flag duplicate rows with a new field called "Duplicate" and a value of Y in it.
Another solution would be to use table aliases, like so:
SELECT p1.id, p2.id, p1.address
FROM list AS p1, list AS p2
WHERE p1.address = p2.address
AND p1.id != p2.id
All you're really doing in this case is taking the original list table, creating two pretend tables -- p1 and p2 -- out of that, and then performing a join on the address column (line 3). The 4th line makes sure that the same record doesn't show up multiple times in your set of results ("duplicate duplicates").
Not going to be very efficient, but it should work:
SELECT *
FROM list AS outer
WHERE (SELECT COUNT(*)
FROM list AS inner
WHERE inner.address = outer.address) > 1;
This will select duplicates in one table pass, no subqueries.
SELECT *
FROM (
SELECT ao.*, (#r := #r + 1) AS rn
FROM (
SELECT #_address := 'N'
) vars,
(
SELECT *
FROM
list a
ORDER BY
address, id
) ao
WHERE CASE WHEN #_address <> address THEN #r := 0 ELSE 0 END IS NOT NULL
AND (#_address := address ) IS NOT NULL
) aoo
WHERE rn > 1
This query actially emulates ROW_NUMBER() present in Oracle and SQL Server
See the article in my blog for details:
Analytic functions: SUM, AVG, ROW_NUMBER - emulating in MySQL.
This also will show you how many duplicates have and will order the results without joins
SELECT `Language` , id, COUNT( id ) AS how_many
FROM `languages`
GROUP BY `Language`
HAVING how_many >=2
ORDER BY how_many DESC
SELECT firstname, lastname, address FROM list
WHERE
Address in
(SELECT address FROM list
GROUP BY address
HAVING count(*) > 1)
select * from table_name t1 inner join (select distinct <attribute list> from table_name as temp)t2 where t1.attribute_name = t2.attribute_name
For your table it would be something like
select * from list l1 inner join (select distinct address from list as list2)l2 where l1.address=l2.address
This query will give you all the distinct address entries in your list table... I am not sure how this will work if you have any primary key values for name, etc..
Fastest duplicates removal queries procedure:
/* create temp table with one primary column id */
INSERT INTO temp(id) SELECT MIN(id) FROM list GROUP BY (isbn) HAVING COUNT(*)>1;
DELETE FROM list WHERE id IN (SELECT id FROM temp);
DELETE FROM temp;
Personally this query has solved my problem:
SELECT `SUB_ID`, COUNT(SRV_KW_ID) as subscriptions FROM `SUB_SUBSCR` group by SUB_ID, SRV_KW_ID HAVING subscriptions > 1;
What this script does is showing all the subscriber ID's that exists more than once into the table and the number of duplicates found.
This are the table columns:
| SUB_SUBSCR_ID | int(11) | NO | PRI | NULL | auto_increment |
| MSI_ALIAS | varchar(64) | YES | UNI | NULL | |
| SUB_ID | int(11) | NO | MUL | NULL | |
| SRV_KW_ID | int(11) | NO | MUL | NULL | |
Hope it will be helpful for you either!
SELECT t.*,(select count(*) from city as tt where tt.name=t.name) as count FROM `city` as t where (select count(*) from city as tt where tt.name=t.name) > 1 order by count desc
Replace city with your Table.
Replace name with your field name
SELECT id, count(*) as c
FROM 'list'
GROUP BY id HAVING c > 1
This will return you the id with the number of times that id is repeated, or nothing in which case you will not have repeated id.
Change the id in the group by (ex: address) and it will return the number of times an address is repeated identified by the first found id with that address.
SELECT id, count(*) as c
FROM 'list'
GROUP BY address HAVING c > 1
I hope it helps. Enjoy ;)
SELECT *
FROM (SELECT address, COUNT(id) AS cnt
FROM list
GROUP BY address
HAVING ( COUNT(id) > 1 ))
I use the following:
SELECT * FROM mytable
WHERE id IN (
SELECT id FROM mytable
GROUP BY column1, column2, column3
HAVING count(*) > 1
)
Most of the answers here don't cope with the case when you have MORE THAN ONE duplicate result and/or when you have MORE THAN ONE column to check for duplications. When you are in such case, you can use this query to get all duplicate ids:
SELECT address, email, COUNT(*) AS QUANTITY_DUPLICATES, GROUP_CONCAT(id) AS ID_DUPLICATES
FROM list
GROUP BY address, email
HAVING COUNT(*)>1;
If you want to list every result as a single line, you need a more complex query. This is the one I found working:
CREATE TEMPORARY TABLE IF NOT EXISTS temptable AS (
SELECT GROUP_CONCAT(id) AS ID_DUPLICATES
FROM list
GROUP BY address, email
HAVING COUNT(*)>1
);
SELECT d.*
FROM list AS d, temptable AS t
WHERE FIND_IN_SET(d.id, t.ID_DUPLICATES)
ORDER BY d.id;
Find duplicate Records:
Suppose we have table : Student
student_id int
student_name varchar
Records:
+------------+---------------------+
| student_id | student_name |
+------------+---------------------+
| 101 | usman |
| 101 | usman |
| 101 | usman |
| 102 | usmanyaqoob |
| 103 | muhammadusmanyaqoob |
| 103 | muhammadusmanyaqoob |
+------------+---------------------+
Now we want to see duplicate records
Use this query:
select student_name,student_id ,count(*) c from student group by student_id,student_name having c>1;
+--------------------+------------+---+
| student_name | student_id | c |
+---------------------+------------+---+
| usman | 101 | 3 |
| muhammadusmanyaqoob | 103 | 2 |
+---------------------+------------+---+
To quickly see the duplicate rows you can run a single simple query
Here I am querying the table and listing all duplicate rows with same user_id, market_place and sku:
select user_id, market_place,sku, count(id)as totals from sku_analytics group by user_id, market_place,sku having count(id)>1;
To delete the duplicate row you have to decide which row you want to delete. Eg the one with lower id (usually older) or maybe some other date information. In my case I just want to delete the lower id since the newer id is latest information.
First double check if the right records will be deleted. Here I am selecting the record among duplicates which will be deleted (by unique id).
select a.user_id, a.market_place,a.sku from sku_analytics a inner join sku_analytics b where a.id< b.id and a.user_id= b.user_id and a.market_place= b.market_place and a.sku = b.sku;
Then I run the delete query to delete the dupes:
delete a from sku_analytics a inner join sku_analytics b where a.id< b.id and a.user_id= b.user_id and a.market_place= b.market_place and a.sku = b.sku;
Backup, Double check, verify, verify backup then execute.
SELECT * FROM bookings
WHERE DATE(created_at) = '2022-01-11'
AND code IN (
SELECT code FROM bookings
GROUP BY code
HAVING COUNT(code) > 1
) ORDER BY id DESC
Would go with something like this:
SELECT t1.firstname t1.lastname t1.address FROM list t1
INNER JOIN list t2
WHERE
t1.id < t2.id AND
t1.address = t2.address;
select address from list where address = any (select address from (select address, count(id) cnt from list group by address having cnt > 1 ) as t1) order by address
the inner sub-query returns rows with duplicate address then
the outer sub-query returns the address column for address with duplicates.
the outer sub-query must return only one column because it used as operand for the operator '= any'
Powerlord answer is indeed the best and I would recommend one more change: use LIMIT to make sure db would not get overloaded:
SELECT firstname, lastname, list.address FROM list
INNER JOIN (SELECT address FROM list
GROUP BY address HAVING count(id) > 1) dup ON list.address = dup.address
LIMIT 10
It is a good habit to use LIMIT if there is no WHERE and when making joins. Start with small value, check how heavy the query is and then increase the limit.