I'd like to perform a cleanup in one of my MySQL Drupal tables to remove duplicate values stored. Here is the structure:
NID VID DELTA FIELD_VALUE
100 100 0 foobar
100 100 1 foobar
101 101 0 barbar
101 101 1 barbar
102 102 0 foofoo
My goal is to remove rows with bigger DELTAs if a row with the same NID, VID, FIELD_VALUE exists with smaller DELTA.
My first attempt was the following query:
delete from mytable a where a.delta=1 and 1=(select count(nid) from mytable b where b.nid=a.nid and b.vid=a.vid and b.delta=0 and b.field_value=a.field_value)
Unfortunately the DB says: (MySQL 5.1.65-cll)
#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'a where a.delta=1 and 1 = (select count from `field_value` b where' at line 1
which is not very helpful to me.
UPDATE:
A deleted answer told me that MySQL does not support alias in delete statements, but removing aliases did not help. The subquery is ok, checked separately.
How about this one?
DELETE a
FROM mytable a
JOIN mytable b ON (a.nid = b.nid
AND a.vid = b.vid
AND a.field_value = b.field_value)
WHERE a.delta > b.delta
(don't forget to backup your data)
Join the table to itself on three columns (NID, VID, FIELD_VALUE) and SELECT the MAX value for DELTA.
This will work as long as you don't have any other columns involved.
Here is a good example for this
Related
I have a some entries in database table rows as follows.
101 - 1
101 - 2
101 - 3
102 - 1
102 - 2
102 - 3
103
I need to get the result of SELECT Query for count as '3' since there are 101 and 102 are the only number before the -.
So is there any way to find the unique value in db table columns before a character?
EDIT : I have entries even without the - .
In case your entries have always the format you have provided us, you just have to find the position of the '-' character, split the values, get the first n characters and count the distinct values
This works for SQL Server, otherwise informs us about what DBMS you are using or replace the functions with the ones of your DBMS on your own
SELECT COUNT(DISTINCT SUBSTRING(val,0,CHARINDEX('-', val))) from YourTable
create table T1
(
id int primary key identity,
col1 varchar(20)
)
insert into T1 values('101 - 1'),('101 - 2'),('101 - 3'),('102 - 1'),('102 - 2'),('102 - 3')
select SUBSTRING(col1,0,CHARINDEX(' ',col1)) as 'Value',count(*) as 'Count' from T1 group by SUBSTRING(col1,0,CHARINDEX(' ',col1))
I have following data in MySQL table named info:
chapter | section
3 | 0
3 | 1
3 | 2
3 | 3
4 | 0
5 | 0
I would like to delete a row for chapter = n, but only when there is no section>0 for same chapter. So chapter 3 can't be deleted while chapter 4 and 5 can. I know the following doesn't work:
DELETE info WHERE chapter = 3 AND NOT EXISTS (SELECT * FROM info WHERE chapter = 3 AND section>0);
The same table is used twice in the statement. So what is the easiest way to achieve my goal?
You've got the idea right. Here is the syntax:
DELETE
FROM mytable
WHERE chapter NOT IN (
SELECT * FROM (
select tt.chapter
from mytable tt
where tt.section <> 0
group by tt.chapter
) tmp
)
The nested select is a workaround a bug in MySQL.
Demo.
You can run a sub query to return the rows that have sections of more then one and then delete the rows returned from the sub query.
DELETE FROM table1 WHERE table1.chapter Not IN (select chapter from
(SELECT table1.chapter FROM table1 WHERE Table1.section >=1 ) Results);
Example Fiddle based on your question
You could also supply the chapter as well in the sub query where clause if you only want to delete a specfic chapter. If it does not meet the where clause then no records will be deleted.
This should do it.
DELETE FROM Table t
WHERE NOT EXISTS(
SELECT 1
FROM Table t2
Where t2.chapter = t.chapter
And t2.section > 0
)
In my experience Exists generally performs better than In. If you are storing a large amount of records you should take this into consideration.
I am using mysql DB server ..
I have the following table that consists of only one column with the following data (where 0's separate sorted integers)
Number
-------
0
1
2
3
0
4
5
0
6
7
8
0
9
10
0
11
I want to get the first value that comes after each 0 , so e.g. output would be
Output
------
1
4
6
9
11
MySQL doesn't guarantee a return order unless you specify a ORDER BY clause. If you get the values back in the order you insert them then that's just coincidence. As it stands there's no way to do what you want to do reliably. You need to add something to order the data by. An ID field set to autoincrement will probably do.
SELECT id1 FROM table WHERE id IN
(SELECT t1.id+1 FROM table t1
LEFT JOIN table t2 ON t1.id1=t2.id
WHERE t2.id1 IS NULL);
SQL Fiddle
Assuming no gaps in the increment field,but since it will be created..
First of all you should add Auto_increment key to your table to guarantee order of records.
Alter table T ADD id INT PRIMARY KEY AUTO_INCREMENT;
And here is the query:
select * from T as T1
Where (SELECT Number From T where Id<T1.Id ORDER BY ID DESC LIMIT 1) = 0
order by ID
SQL Fiddle demo
I thought I had a very simple query to perform, but I can't seem to make it work.
I have this table with 2 columns:
version_id trim_id
1 15
1 25
1 28
1 30
1 35
2 12
2 25
2 33
2 48
3 11
3 25
3 30
3 32
I am trying to get any version-id's that have say a sub-set of trim_id's. Let's say all version_id's that have trim_id's 25 and 30. My obvious attempt was :
SELECT * FROM table WHERE trim_id=25 AND trim_id=30
I was expecting to have version_id 1 and 3 as a result, but instead I get nothing.
I am working with the latest version of MAMP, which has some odd behavior, like in this case it just tells me its 'LOADING' and never gives me an error message or something. But that's normally the case when there is no data to return.
This is InnoDB, if that helps.
Thanks for your input.
Your query does not work because you are using AND and the trim_id cannot have two different values at the same time, so you need to apply Relational Division to get the result.
You will need to use something similar to the following:
SELECT version_id
FROM yourtable
WHERE trim_id in (25, 30)
group by version_id
having count(distinct trim_id) = 2
See SQL Fiddle with Demo.
This will return the version_id values that have both 25 and 30. Then if you wanted to include additional columns in the final result, you can expand the query to:
select t1.version_id, t1.trim_id
from yourtable t1
where exists (SELECT t2.version_id
FROM yourtable t2
WHERE t2.trim_id in (25, 30)
and t1.version_id = t2.version_id
group by t2.version_id
having count(distinct t2.trim_id) = 2);
See SQL Fiddle with Demo
SELECT *
FROM table
WHERE trim_id IN(25,30)
when I DELETE, as example, the id 3, I have this:
id | name
1 |
2 |
4 |
5 |
...
now, I want to search for the missing id(s), because i want to fill the id again with:
INSERT INTO xx (id,...) VALUES (3,...)
is there a way to search for "holes" in the auto_increment index?
thanks!
You can find the top value of gaps like this:
select t1.id - 1 as missing_id
from mytable t1
left join mytable t2 on t2.id = t1.id - 1
where t2.id is null
The purpose of AUTO_INCREMENT is to generate simple unique and meaningless identifiers for your rows. As soon as you plan to re-use those IDs, they're no longer unique (not at least in time) so I have the impression that you are not using the right tool for the job. If you decide to get rid of AUTO_INCREMENT, you can do all your inserts with the same algorithm.
As about the SQL code, this query will match existing rows with the rows that has the next ID:
SELECT a.foo_id, b.foo_id
FROM foo a
LEFT JOIN foo b ON a.foo_id=b.foo_id-1
E.g.:
1 NULL
4 NULL
10 NULL
12 NULL
17 NULL
19 20
20 NULL
24 25
25 26
26 27
27 NULL
So it's easy to filter out rows and get the first gap:
SELECT MIN(a.foo_id)+1 AS next_id
FROM foo a
LEFT JOIN foo b ON a.foo_id=b.foo_id-1
WHERE b.foo_id IS NULL
Take this as a starting point because it still needs some tweaking:
You need to consider the case where the lowest available number is the lowest possible one.
You need to lock the table to handle concurrent inserts.
In my computer it's slow as hell with big tables.
I think the only way you can do this is with a loop:
Any other solutions wont show gaps bigger than 1:
insert into XX values (1)
insert into XX values (2)
insert into XX values (4)
insert into XX values (5)
insert into XX values (10)
declare #min int
declare #max int
select #min=MIN(ID) from xx
select #max=MAX(ID) from xx
while #min<#max begin
if not exists(select 1 from XX where id = #min+1) BEGIN
print 'GAP: '+ cast(#min +1 as varchar(10))
END
set #min=#min+1
end
result:
GAP: 3
GAP: 6
GAP: 7
GAP: 8
GAP: 9
First, I agree with the comments that you shouldn't try filling in holes. You won't be able to find all the holes with a single SQL statement. You'll have to loop through all possible numbers starting with 1 until you find a hole. You could write a sql function to do this for you that could then be used in a function. So if you wrote a function called find_first_hole you could then call it in an insert like:
INSERT INTO xx (id, ...) VALUES (find_first_hole(), ...)
This is a gaps&island problem, see my (and other) replies here and here. In most cases, gaps&islands problems are most elegantly solved using recursive CTE's, which are not available in mysql.