I wasn't sure how to word my question, but here we go... With an example of what I'm trying to achieve.
I have a table, which looks like this:
-------------------
X_ID | Y_ID
-------------------
2 | 8
2 | 12
--------------------
I want to return one row per X_ID, which has only one Y_ID for that X_ID.
I don't want to return a row if it has > 1 Y_ID, for a particular X_ID. And, I want to return only one row out of all X_IDs that match the above rule.
Using the table above as an example, I need a query that would return 0 rows for the data in that table.
I need the same query to return 1 row from the following table
-------------------
X_ID | Y_ID
-------------------
2 | 8
2 | 12
3 | 19
3 | 19
-------------------
I need a query that will return one row form this - either of the bottom 2.
I just need the X_ID.
I've tried just about as much as I can think of, using DISTINCT and GROUP BY.
Any ideas?
Oddly, this would be more complicated in MSSQL since it would require you to group on X_ID and Y_ID; but this should work. Normally, the Y_ID in the results would be an effectively random selection of all the Y_ID values found in that group; but since we are specifically filtering out groups with more than one Y_ID, it ends up being the exact Y_ID you need.
SELECT X_ID, Y_ID
FROM (
SELECT X_ID, Y_ID, COUNT(DISTINCT Y_ID) AS yCount
FROM theTable
GROUP BY X_ID
HAVING yCount = 1
) AS subQ
;
I'm not quite as well versed in the intricacies of MSSQL, but I think something this would work (for both MySQL and MSSQL).
SELECT t1.X_ID, t1.Y_ID
FROM theTable AS t1
INNER JOIN (
SELECT X_ID, COUNT(DISTINCT Y_ID) AS yCount
FROM theTable
GROUP BY X_ID
HAVING COUNT(DISTINCT Y_ID) = 1
) AS t2 ON X_ID
;
I say think because I am not 100% sure MSSQL supports COUNT(DISTINCT value).
You can try this. It should do what you want it to do.
SELECT X_ID, Y_ID FROM theTable
GROUP BY X_ID
HAVING COUNT(DISTINCT X_ID, Y_ID) = 1
Related
Is there any way to get the inverse of a group by statement in mysql? My use case is to delete all duplicates.
Say my table looks like this:
ID | columnA | ...
1 | A
2 | A
3 | A
4 | B
5 | B
6 | C
I want my result set to look like this:
ID | columnA | ...
2 | A
3 | A
5 | B
(Essentially this finds all duplicates leaving one behind. Could be used to purge all duplicate records down to 1, or to perform other analysis later).
One way is to take all but the first id for each value of ColumnA:
select t.*
from t
where t.id > (select min(t2.id) from t t2 where t2.columnA = t.columnA);
Your result seems
select max(id), columnA group by columnA
This should perform a lot better then inner select based queries.
SELECT
*
FROM
TABLE
QUALIFY
RANK() OVER (partition by columnA order by ID ASC ) = 1
EDIT : This apparently wont work in MySQL. Guess the only answer is to by a oracle license - or use another answer. ;)
I realized my own solution based on #scaisEdge response before he edited it. In need the opposite of my group by, so using a subquery:
SELECT * FROM mytable WHERE ID NOT IN (SELECT ID FROM mytable GROUP BY columnA);
I am confident this will help.
create table test.temptable select distinct * from YourTable;
truncate YourTable;
insert into YourTable select * from test.temptable ;
MODE is the value that occurs the MOST times in the data, there can be ONE MODE or MANY MODES
here's some values in two tables (sqlFiddle)
create table t100(id int auto_increment primary key, value int);
create table t200(id int auto_increment primary key, value int);
insert into t100(value) values (1),
(2),(2),(2),
(3),(3),
(4);
insert into t200(value) values (1),
(2),(2),(2),
(3),(3),
(4),(4),(4);
right now, to get the MODE(S) returned as comma separated list, I run the below query for table t100
SELECT GROUP_CONCAT(value) as modes,occurs
FROM
(SELECT value,occurs FROM
(SELECT value,count(*) as occurs
FROM
T100
GROUP BY value)T1,
(SELECT max(occurs) as maxoccurs FROM
(SELECT value,count(*) as occurs
FROM
T100
GROUP BY value)T2
)T3
WHERE T1.occurs = T3.maxoccurs)T4
GROUP BY occurs;
and the below query for table t200 (same query just with table name changed) I have 2 tables in this example because to show that it works for cases where there's 1 MODE and where there are multiple MODES.
SELECT GROUP_CONCAT(value) as modes,occurs
FROM
(SELECT value,occurs FROM
(SELECT value,count(*) as occurs
FROM
T200
GROUP BY value)T1,
(SELECT max(occurs) as maxoccurs FROM
(SELECT value,count(*) as occurs
FROM
T200
GROUP BY value)T2
)T3
WHERE T1.occurs = T3.maxoccurs)T4
GROUP BY occurs;
My question is "Is there a simpler way?"
I was thinking like using HAVING count(*) = max(count(*)) or something similar to get rid of the extra join but couldn't get HAVING to return the result i wanted.
UPDATED:
as suggested by #zneak, I can simplify T3 like below:
SELECT GROUP_CONCAT(value) as modes,occurs
FROM
(SELECT value,occurs FROM
(SELECT value,count(*) as occurs
FROM
T200
GROUP BY value)T1,
(SELECT count(*) as maxoccurs
FROM
T200
GROUP BY value
ORDER BY count(*) DESC
LIMIT 1
)T3
WHERE T1.occurs = T3.maxoccurs)T4
GROUP BY occurs;
Now is there a way to get ride of T3 altogether?
I tried this but it returns no rows for some reason
SELECT value,occurs FROM
(SELECT value,count(*) as occurs
FROM t200
GROUP BY `value`)T1
HAVING occurs=max(occurs)
basically I am wondering if there's a way to do it such that I only need to specify t100 or t200 once.
UPDATED: i found a way to specify t100 or t200 only once by adding a variable to set my own maxoccurs like below
SELECT GROUP_CONCAT(CASE WHEN occurs=#maxoccurs THEN value ELSE NULL END) as modes
FROM
(SELECT value,occurs,#maxoccurs:=GREATEST(#maxoccurs,occurs) as maxoccurs
FROM (SELECT value,count(*) as occurs
FROM t200
GROUP BY `value`)T1,(SELECT #maxoccurs:=0)mo
)T2
You are very close with the last query. The following finds one mode:
SELECT value, occurs
FROM (SELECT value,count(*) as occurs
FROM t200
GROUP BY `value`
LIMIT 1
) T1
I think your question was about multiple modes, though:
SELECT value, occurs
FROM (SELECT value, count(*) as occurs
FROM t200
GROUP BY `value`
) T1
WHERE occurs = (select max(occurs)
from (select `value`, count(*) as occurs
from t200
group by `value`
) t
);
EDIT:
This is much easier in almost any other database. MySQL supports neither with nor window/analytic functions.
Your query (shown below) does not do what you think it is doing:
SELECT value, occurs
FROM (SELECT value, count(*) as occurs
FROM t200
GROUP BY `value`
) T1
HAVING occurs = max(occurs) ;
The final having clause refers to the variable occurs but does use max(occurs). Because of the use of max(occurs) this is an aggregation query that returns one row, summarizing all rows from the subquery.
The variable occurs is not using for grouping. So, what value does MySQL use? It uses an arbitrary value from one of the rows in the subquery. This arbitrary value might match, or it might not. But, the value only comes from one row. There is no iteration over it.
I realize this is a very old question but in looking for the best way to find the MODE in a MySQL table, I came up with this:
SELECT [column name], count(*) as [ccount] FROM [table] WHERE [field] = [item] GROUP BY [column name] ORDER BY [ccount] DESC LIMIT 1 ;
In my actual situation, I had a log with recorded events in it. I wanted to know during which period (1, 2 or 3 as recorded in my log) the specific event occurred the most number of times. (Eg, the MODE of "period" column of the table for that specific event
My table looked like this (abridged):
EVENT_TYPE | PERIOD
-------------------------
1 | 3
1 | 3
1 | 3
1 | 2
2 | 1
2 | 1
2 | 1
2 | 3
Using the query:
SELECT event_type, period, count(*) as pcount FROM proto_log WHERE event_type = 1 GROUP BY period ORDER BY pcount DESC LIMIT 1 ;
I get the result:
> EVENT_TYPE | PERIOD | PCOUNT
> --------------------------------------
1 | 3 | 3
Using this result, the period column ($result['period'] for example) should contain the MODE for that query and of course pcount contains the actual count.
If you wanted to get multiple modes, I suppse you could keep adding other criteria to your WHERE clause using ORs:
SELECT event_type, period, count(*) as pcount FROM proto_log WHERE event_type = 1 ***OR event_type = 2*** GROUP BY period ORDER BY pcount DESC LIMIT 2 ;
The multiple ORs should give you the additional results and the LIMIT increase will add the additional MODES to the results. (Otherwise it will still only show the top 1 result)
Results:
EVENT_TYPE | PERIOD | PCOUNT
--------------------------------------
1 | 3 | 3
2 | 1 | 3
I am not 100% sure this is doing exactly what I think it is doing, or if it will work in all situations, so please let me know if I am on or off track here.
I have a MySQL table like this
id Name count
1 ABC 1
2 CDF 3
3 FGH 4
using simply select query I get the values as
1 ABC 1
2 CDF 3
3 FGH 4
How I can get the result like this
1 ABC 1
2 CDF 3
3 FGH 4
4 NULL 0
You can see Last row. When Records are finished an extra row in this format
last_id+1, Null ,0 should be added. You can see above. Even I have no such row in my original table. There may be N rows not fixed 3,4
The answer is very simple
select (select max(id) from mytable)+1 as id, NULL as Name, 0 as count union all select id,Name,count from mytable;
This looks a little messy but it should work.
SELECT a.id, b.name, coalesce(b.`count`) as `count`
FROM
(
SELECT 1 as ID
UNION
SELECT 2 as ID
UNION
SELECT 3 as ID
UNION
SELECT 4 as ID
) a LEFT JOIN table1 b
ON a.id = b.id
WHERE a.ID IN (1,2,3,4)
UPDATE 1
You could simply generate a table that have 1 column preferably with name (ID) that has records maybe up 10,000 or more. Then you could simply join it with your table that has the original record. For Example, assuming that you have a table named DummyRecord with 1 column and has 10,000 rows on it
SELECT a.id, b.name, coalesce(b.`count`) as `count`
FROM DummyRecord a LEFT JOIN table1 b
ON a.id = b.id
WHERE a.ID >= 1 AND
a.ID <= 4
that's it. Or if you want to have from 10 to 100, then you could use this condition
...
WHERE a.ID >= 10 AND
a.ID <= 100
To clarify this is how one can append an extra row to the result set
select * from table union select 123 as id,'abc' as name
results
id | name
------------
*** | ***
*** | ***
123 | abc
Simply use mysql ROLLUP.
SELECT * FROM your_table
GROUP BY Name WITH ROLLUP;
select
x.id,
t.name,
ifnull(t.count, 0) as count
from
(SELECT 1 AS id
-- Part of the query below, you will need to generate dynamically,
-- just as you would otherwise need to generate 'in (1,2,3,4)'
UNION ALL SELECT 2
UNION ALL SELECT 3
UNION ALL SELECT 4
UNION ALL SELECT 5
) x
LEFT JOIN YourTable t
ON t.id = x.id
If the id does not exist in the table you're selecting from, you'll need to LEFT JOIN against a list of every id you want returned - this way, it will return the null values for ones that don't exist and the true values for those that do.
I would suggest creating a numbers table that is a single-columned table filled with numbers:
CREATE TABLE `numbers` (
id int(11) unsigned NOT NULL
);
And then inserting a large amount of numbers, starting at 1 and going up to what you think the highest id you'll ever see plus a thousand or so. Maybe go from 1 to 1000000 to be on the safe side. Regardless, you just need to make sure it's more-than-high enough to cover any possible id you'll run into.
After that, your query can look like:
SELECT n.id, a.*
FROM
`numbers` n
LEFT JOIN table t
ON t.id = n.id
WHERE n.id IN (1,2,3,4);
This solution will allow for a dynamically growing list of ids without the need for a sub-query with a list of unions; though, the other solutions provided will equally work for a small known list too (and could also be dynamically generated).
I have a table student like this
id | name | zip
1 | abc | 1234
2 | xyz | 4321
3 | asd | 1234
I want to get all records but zip code should not be repeated. So In case of above table records, record No 1 and 2 should be fetched. Record No. 3 will not be fetched because it has a zip code which is already in record No. 1
SELECT DISTINCT fieldName FROM tableName;
The following query will only select distinct 'zip' field.
SELECT DISTINCT zip FROM student;
SELECT * FROM tableName GROUP BY fieldName;
The following query will select all fields along with distinct zip field.
SELECT * FROM student GROUP BY zip;
TRY
SELECT DISTINCT(zip),id,name FROM student;
OR
SELECT * FROM student GROUP BY zip;
Altough in MySQL you can get away with:
SELECT *
FROM student
GROUP BY zip
I would choose:
SELECT *
FROM student t
JOIN
( SELECT MIN(id) AS minid
FROM student
GROUP BY zip
) AS grp
ON grp.minid = t.id
Since presumably the other columns are of some interest....
SELECT y.*
FROM yourTable y,
(SELECT MIN(y2.id)
FROM yourTable y2
GROUP BY y2.zip) ilv
WHERE ilv.id=y.id;
(or you could use the max-concat trick)
update
Oracle have now removed the max concat trick from the linked page - but it is described elsewhere on the internet
Try Using
Select Distinct(zip),id,name group by zip;
Is there any problem if I use as this below?
select distinct zip,name,id from student;
select id, name, distinct(zip) from student;
I'm trying to figure out a way to return results by using the group by function.
GROUP BY is working as expected, but my question is: Is it possible to have a group by ignoring the NULL field. So that it does not group NULLs together because I still need all the rows where the specified field is NULL.
SELECT `table1`.*,
GROUP_CONCAT(id SEPARATOR ',') AS `children_ids`
FROM `table1`
WHERE (enabled = 1)
GROUP BY `ancestor`
So now let's say I have 5 rows and the ancestor field is NULL, it returns me 1 row....but I want all 5.
Perhaps you should add something to the null columns to make them unique and group on that? I was looking for some sort of sequence to use instead of UUID() but this might work just as well.
SELECT `table1`.*,
IFNULL(ancestor,UUID()) as unq_ancestor
GROUP_CONCAT(id SEPARATOR ',') AS `children_ids`
FROM `table1`
WHERE (enabled = 1)
GROUP BY unq_ancestor
When grouping by column Y, all rows for which the value in Y is NULL are grouped together.
This behaviour is defined by the SQL-2003 standard, though it's slightly surprising because NULL is not equal to NULL.
You can work around it by grouping on a different value, some function (mathematically speaking) of the data in your grouping column.
If you have a unique column X then this is easy.
Input
X Y
-------------
1 a
2 a
3 b
4 b
5 c
6 (NULL)
7 (NULL)
8 d
Without fix
SELECT GROUP_CONCAT(`X`)
FROM `tbl`
GROUP BY `Y`;
Result:
GROUP_CONCAT(`foo`)
-------------------
6,7
1,2
3,4
5
8
With fix
SELECT GROUP_CONCAT(`X`)
FROM `tbl`
GROUP BY IFNULL(`Y`, `X`);
Result:
GROUP_CONCAT(`foo`)
-------------------
6
7
1,2
3,4
5
8
Let's take a closer look at how this is working
SELECT GROUP_CONCAT(`X`), IFNULL(`Y`, `X`) AS `grp`
FROM `tbl`
GROUP BY `grp`;
Result:
GROUP_CONCAT(`foo`) `grp`
-----------------------------
6 6
7 7
1,2 a
3,4 b
5 c
8 d
If you don't have a unique column that you can use, you can try to generate a unique placeholder value instead. I'll leave this as an exercise to the reader.
GROUP BY IFNULL(required_field, id)
SELECT table1.*,
GROUP_CONCAT(id SEPARATOR ',') AS children_ids
FROM table1
WHERE (enabled = 1)
GROUP BY ancestor
, CASE WHEN ancestor IS NULL
THEN table1.id
ELSE 0
END
Maybe faster version of previous solution in case you have unique identifier in table1 (let suppose it is table1.id) :
SELECT `table1`.*,
GROUP_CONCAT(id SEPARATOR ',') AS `children_ids`,
IF(ISNULL(ancestor),table1.id,NULL) as `do_not_group_on_null_ancestor`
FROM `table1`
WHERE (enabled = 1)
GROUP BY `ancestor`, `do_not_group_on_null_ancestor`
To union multiple tables and group_concat different column and a sum of the column for the (unique primary or foreign key) column to display a value in the same row
select column1,column2,column3,GROUP_CONCAT(if(column4='', null, column4)) as
column4,sum(column5) as column5
from (
select column1,group_concat(column2) as column2,sum(column3 ) as column3,'' as
column4,'' as column5
from table1
group by column1
union all
select column1,'' as column2,'' as column3,group_concat(column4) as
column4,sum(column5) as column5
from table 2
group by column1
) as t
group by column1