I'd like to find the first "gap" in a counter column in an SQL table. For example, if there are values 1,2,4 and 5 I'd like to find out 3.
I can of course get the values in order and go through it manually, but I'd like to know if there would be a way to do it in SQL.
In addition, it should be quite standard SQL, working with different DBMSes.
In MySQL and PostgreSQL:
SELECT id + 1
FROM mytable mo
WHERE NOT EXISTS
(
SELECT NULL
FROM mytable mi
WHERE mi.id = mo.id + 1
)
ORDER BY
id
LIMIT 1
In SQL Server:
SELECT TOP 1
id + 1
FROM mytable mo
WHERE NOT EXISTS
(
SELECT NULL
FROM mytable mi
WHERE mi.id = mo.id + 1
)
ORDER BY
id
In Oracle:
SELECT *
FROM (
SELECT id + 1 AS gap
FROM mytable mo
WHERE NOT EXISTS
(
SELECT NULL
FROM mytable mi
WHERE mi.id = mo.id + 1
)
ORDER BY
id
)
WHERE rownum = 1
ANSI (works everywhere, least efficient):
SELECT MIN(id) + 1
FROM mytable mo
WHERE NOT EXISTS
(
SELECT NULL
FROM mytable mi
WHERE mi.id = mo.id + 1
)
Systems supporting sliding window functions:
SELECT -- TOP 1
-- Uncomment above for SQL Server 2012+
previd
FROM (
SELECT id,
LAG(id) OVER (ORDER BY id) previd
FROM mytable
) q
WHERE previd <> id - 1
ORDER BY
id
-- LIMIT 1
-- Uncomment above for PostgreSQL
Your answers all work fine if you have a first value id = 1, otherwise this gap will not be detected. For instance if your table id values are 3,4,5, your queries will return 6.
I did something like this
SELECT MIN(ID+1) FROM (
SELECT 0 AS ID UNION ALL
SELECT
MIN(ID + 1)
FROM
TableX) AS T1
WHERE
ID+1 NOT IN (SELECT ID FROM TableX)
There isn't really an extremely standard SQL way to do this, but with some form of limiting clause you can do
SELECT `table`.`num` + 1
FROM `table`
LEFT JOIN `table` AS `alt`
ON `alt`.`num` = `table`.`num` + 1
WHERE `alt`.`num` IS NULL
LIMIT 1
(MySQL, PostgreSQL)
or
SELECT TOP 1 `num` + 1
FROM `table`
LEFT JOIN `table` AS `alt`
ON `alt`.`num` = `table`.`num` + 1
WHERE `alt`.`num` IS NULL
(SQL Server)
or
SELECT `num` + 1
FROM `table`
LEFT JOIN `table` AS `alt`
ON `alt`.`num` = `table`.`num` + 1
WHERE `alt`.`num` IS NULL
AND ROWNUM = 1
(Oracle)
The first thing that came into my head. Not sure if it's a good idea to go this way at all, but should work. Suppose the table is t and the column is c:
SELECT
t1.c + 1 AS gap
FROM t as t1
LEFT OUTER JOIN t as t2 ON (t1.c + 1 = t2.c)
WHERE t2.c IS NULL
ORDER BY gap ASC
LIMIT 1
Edit: This one may be a tick faster (and shorter!):
SELECT
min(t1.c) + 1 AS gap
FROM t as t1
LEFT OUTER JOIN t as t2 ON (t1.c + 1 = t2.c)
WHERE t2.c IS NULL
This works in SQL Server - can't test it in other systems but it seems standard...
SELECT MIN(t1.ID)+1 FROM mytable t1 WHERE NOT EXISTS (SELECT ID FROM mytable WHERE ID = (t1.ID + 1))
You could also add a starting point to the where clause...
SELECT MIN(t1.ID)+1 FROM mytable t1 WHERE NOT EXISTS (SELECT ID FROM mytable WHERE ID = (t1.ID + 1)) AND ID > 2000
So if you had 2000, 2001, 2002, and 2005 where 2003 and 2004 didn't exist, it would return 2003.
The following solution:
provides test data;
an inner query that produces other gaps; and
it works in SQL Server 2012.
Numbers the ordered rows sequentially in the "with" clause and then reuses the result twice with an inner join on the row number, but offset by 1 so as to compare the row before with the row after, looking for IDs with a gap greater than 1. More than asked for but more widely applicable.
create table #ID ( id integer );
insert into #ID values (1),(2), (4),(5),(6),(7),(8), (12),(13),(14),(15);
with Source as (
select
row_number()over ( order by A.id ) as seq
,A.id as id
from #ID as A WITH(NOLOCK)
)
Select top 1 gap_start from (
Select
(J.id+1) as gap_start
,(K.id-1) as gap_end
from Source as J
inner join Source as K
on (J.seq+1) = K.seq
where (J.id - (K.id-1)) <> 0
) as G
The inner query produces:
gap_start gap_end
3 3
9 11
The outer query produces:
gap_start
3
Inner join to a view or sequence that has a all possible values.
No table? Make a table. I always keep a dummy table around just for this.
create table artificial_range(
id int not null primary key auto_increment,
name varchar( 20 ) null ) ;
-- or whatever your database requires for an auto increment column
insert into artificial_range( name ) values ( null )
-- create one row.
insert into artificial_range( name ) select name from artificial_range;
-- you now have two rows
insert into artificial_range( name ) select name from artificial_range;
-- you now have four rows
insert into artificial_range( name ) select name from artificial_range;
-- you now have eight rows
--etc.
insert into artificial_range( name ) select name from artificial_range;
-- you now have 1024 rows, with ids 1-1024
Then,
select a.id from artificial_range a
where not exists ( select * from your_table b
where b.counter = a.id) ;
This one accounts for everything mentioned so far. It includes 0 as a starting point, which it will default to if no values exist as well. I also added the appropriate locations for the other parts of a multi-value key. This has only been tested on SQL Server.
select
MIN(ID)
from (
select
0 ID
union all
select
[YourIdColumn]+1
from
[YourTable]
where
--Filter the rest of your key--
) foo
left join
[YourTable]
on [YourIdColumn]=ID
and --Filter the rest of your key--
where
[YourIdColumn] is null
For PostgreSQL
An example that makes use of recursive query.
This might be useful if you want to find a gap in a specific range
(it will work even if the table is empty, whereas the other examples will not)
WITH
RECURSIVE a(id) AS (VALUES (1) UNION ALL SELECT id + 1 FROM a WHERE id < 100), -- range 1..100
b AS (SELECT id FROM my_table) -- your table ID list
SELECT a.id -- find numbers from the range that do not exist in main table
FROM a
LEFT JOIN b ON b.id = a.id
WHERE b.id IS NULL
-- LIMIT 1 -- uncomment if only the first value is needed
My guess:
SELECT MIN(p1.field) + 1 as gap
FROM table1 AS p1
INNER JOIN table1 as p3 ON (p1.field = p3.field + 2)
LEFT OUTER JOIN table1 AS p2 ON (p1.field = p2.field + 1)
WHERE p2.field is null;
I wrote up a quick way of doing it. Not sure this is the most efficient, but gets the job done. Note that it does not tell you the gap, but tells you the id before and after the gap (keep in mind the gap could be multiple values, so for example 1,2,4,7,11 etc)
I'm using sqlite as an example
If this is your table structure
create table sequential(id int not null, name varchar(10) null);
and these are your rows
id|name
1|one
2|two
4|four
5|five
9|nine
The query is
select a.* from sequential a left join sequential b on a.id = b.id + 1 where b.id is null and a.id <> (select min(id) from sequential)
union
select a.* from sequential a left join sequential b on a.id = b.id - 1 where b.id is null and a.id <> (select max(id) from sequential);
https://gist.github.com/wkimeria/7787ffe84d1c54216f1b320996b17b7e
Here is an alternative to show the range of all possible gap values in portable and more compact way :
Assume your table schema looks like this :
> SELECT id FROM your_table;
+-----+
| id |
+-----+
| 90 |
| 103 |
| 104 |
| 118 |
| 119 |
| 120 |
| 121 |
| 161 |
| 162 |
| 163 |
| 185 |
+-----+
To fetch the ranges of all possible gap values, you have the following query :
The subquery lists pairs of ids, each of which has the lowerbound column being smaller than upperbound column, then use GROUP BY and MIN(m2.id) to reduce number of useless records.
The outer query further removes the records where lowerbound is exactly upperbound - 1
My query doesn't (explicitly) output the 2 records (YOUR_MIN_ID_VALUE, 89) and (186, YOUR_MAX_ID_VALUE) at both ends, that implicitly means any number in both of the ranges hasn't been used in your_table so far.
> SELECT m3.lowerbound + 1, m3.upperbound - 1 FROM
(
SELECT m1.id as lowerbound, MIN(m2.id) as upperbound FROM
your_table m1 INNER JOIN your_table
AS m2 ON m1.id < m2.id GROUP BY m1.id
)
m3 WHERE m3.lowerbound < m3.upperbound - 1;
+-------------------+-------------------+
| m3.lowerbound + 1 | m3.upperbound - 1 |
+-------------------+-------------------+
| 91 | 102 |
| 105 | 117 |
| 122 | 160 |
| 164 | 184 |
+-------------------+-------------------+
select min([ColumnName]) from [TableName]
where [ColumnName]-1 not in (select [ColumnName] from [TableName])
and [ColumnName] <> (select min([ColumnName]) from [TableName])
Here is standard a SQL solution that runs on all database servers with no change:
select min(counter + 1) FIRST_GAP
from my_table a
where not exists (select 'x' from my_table b where b.counter = a.counter + 1)
and a.counter <> (select max(c.counter) from my_table c);
See in action for;
PL/SQL via Oracle's livesql,
MySQL via sqlfiddle,
PostgreSQL via sqlfiddle
MS Sql via sqlfiddle
It works for empty tables or with negatives values as well. Just tested in SQL Server 2012
select min(n) from (
select case when lead(i,1,0) over(order by i)>i+1 then i+1 else null end n from MyTable) w
If You use Firebird 3 this is most elegant and simple:
select RowID
from (
select `ID_Column`, Row_Number() over(order by `ID_Column`) as RowID
from `Your_Table`
order by `ID_Column`)
where `ID_Column` <> RowID
rows 1
-- PUT THE TABLE NAME AND COLUMN NAME BELOW
-- IN MY EXAMPLE, THE TABLE NAME IS = SHOW_GAPS AND COLUMN NAME IS = ID
-- PUT THESE TWO VALUES AND EXECUTE THE QUERY
DECLARE #TABLE_NAME VARCHAR(100) = 'SHOW_GAPS'
DECLARE #COLUMN_NAME VARCHAR(100) = 'ID'
DECLARE #SQL VARCHAR(MAX)
SET #SQL =
'SELECT TOP 1
'+#COLUMN_NAME+' + 1
FROM '+#TABLE_NAME+' mo
WHERE NOT EXISTS
(
SELECT NULL
FROM '+#TABLE_NAME+' mi
WHERE mi.'+#COLUMN_NAME+' = mo.'+#COLUMN_NAME+' + 1
)
ORDER BY
'+#COLUMN_NAME
-- SELECT #SQL
DECLARE #MISSING_ID TABLE (ID INT)
INSERT INTO #MISSING_ID
EXEC (#SQL)
--select * from #MISSING_ID
declare #var_for_cursor int
DECLARE #LOW INT
DECLARE #HIGH INT
DECLARE #FINAL_RANGE TABLE (LOWER_MISSING_RANGE INT, HIGHER_MISSING_RANGE INT)
DECLARE IdentityGapCursor CURSOR FOR
select * from #MISSING_ID
ORDER BY 1;
open IdentityGapCursor
fetch next from IdentityGapCursor
into #var_for_cursor
WHILE ##FETCH_STATUS = 0
BEGIN
SET #SQL = '
DECLARE #LOW INT
SELECT #LOW = MAX('+#COLUMN_NAME+') + 1 FROM '+#TABLE_NAME
+' WHERE '+#COLUMN_NAME+' < ' + cast( #var_for_cursor as VARCHAR(MAX))
SET #SQL = #sql + '
DECLARE #HIGH INT
SELECT #HIGH = MIN('+#COLUMN_NAME+') - 1 FROM '+#TABLE_NAME
+' WHERE '+#COLUMN_NAME+' > ' + cast( #var_for_cursor as VARCHAR(MAX))
SET #SQL = #sql + 'SELECT #LOW,#HIGH'
INSERT INTO #FINAL_RANGE
EXEC( #SQL)
fetch next from IdentityGapCursor
into #var_for_cursor
END
CLOSE IdentityGapCursor;
DEALLOCATE IdentityGapCursor;
SELECT ROW_NUMBER() OVER(ORDER BY LOWER_MISSING_RANGE) AS 'Gap Number',* FROM #FINAL_RANGE
Found most of approaches run very, very slow in mysql. Here is my solution for mysql < 8.0. Tested on 1M records with a gap near the end ~ 1sec to finish. Not sure if it fits other SQL flavours.
SELECT cardNumber - 1
FROM
(SELECT #row_number := 0) as t,
(
SELECT (#row_number:=#row_number+1), cardNumber, cardNumber-#row_number AS diff
FROM cards
ORDER BY cardNumber
) as x
WHERE diff >= 1
LIMIT 0,1
I assume that sequence starts from `1`.
If your counter is starting from 1 and you want to generate first number of sequence (1) when empty, here is the corrected piece of code from first answer valid for Oracle:
SELECT
NVL(MIN(id + 1),1) AS gap
FROM
mytable mo
WHERE 1=1
AND NOT EXISTS
(
SELECT NULL
FROM mytable mi
WHERE mi.id = mo.id + 1
)
AND EXISTS
(
SELECT NULL
FROM mytable mi
WHERE mi.id = 1
)
DECLARE #Table AS TABLE(
[Value] int
)
INSERT INTO #Table ([Value])
VALUES
(1),(2),(4),(5),(6),(10),(20),(21),(22),(50),(51),(52),(53),(54),(55)
--Gaps
--Start End Size
--3 3 1
--7 9 3
--11 19 9
--23 49 27
SELECT [startTable].[Value]+1 [Start]
,[EndTable].[Value]-1 [End]
,([EndTable].[Value]-1) - ([startTable].[Value]) Size
FROM
(
SELECT [Value]
,ROW_NUMBER() OVER(PARTITION BY 1 ORDER BY [Value]) Record
FROM #Table
)AS startTable
JOIN
(
SELECT [Value]
,ROW_NUMBER() OVER(PARTITION BY 1 ORDER BY [Value]) Record
FROM #Table
)AS EndTable
ON [EndTable].Record = [startTable].Record+1
WHERE [startTable].[Value]+1 <>[EndTable].[Value]
If the numbers in the column are positive integers (starting from 1) then here is how to solve it easily. (assuming ID is your column name)
SELECT TEMP.ID
FROM (SELECT ROW_NUMBER() OVER () AS NUM FROM 'TABLE-NAME') AS TEMP
WHERE ID NOT IN (SELECT ID FROM 'TABLE-NAME')
ORDER BY 1 ASC LIMIT 1
SELECT ID+1 FROM table WHERE ID+1 NOT IN (SELECT ID FROM table) ORDER BY 1;
I have a database table setup like this:
id | code | group_id | status ---
---|-------|---------|------------
1 | abcd1 | group_1 | available
2 | abcd2 | group_1 | available
3 | adsd3 | group_1 | available
4 | dfgd4 | group_1 | available
5 | vfcd5 | group_1 | available
6 | bgcd6 | group_2 | available
7 | abcd7 | group_2 | available
8 | ahgf8 | group_2 | available
9 | dfgd9 | group_2 | available
10 | qwer6 | group_2 | available
In the example above, each group_id has 5 total rows (arbitrary for example, total rows will be dynamic and vary), I need to remove every row that matches available in status except for 2 of them (which 2 does not matter, as long as there are 2 of them remaining)
Basically every unique group_id should only have 2 total rows with status of available. I am able to do a simple SQL query to remove all of them, but struggling to come up with a SQL query to remove all except for 2 ... please helppppp :)
If code is unique, you can use subqueries to keep the "min" and "max"
DELETE FROM t
WHERE t.status = 'available'
AND (t.group_id, t.code) NOT IN (
SELECT group_id, MAX(code)
FROM t
WHERE status = 'available'
GROUP BY group_id
)
AND (t.group_id, t.code) NOT IN (
SELECT group_id, MIN(code)
FROM t
WHERE status = 'available'
GROUP BY group_id
)
Similarly, with an auto increment id:
DELETE FROM t
WHERE t.status = 'available'
AND t.id NOT IN (
SELECT MAX(id) FROM t WHERE status = 'available' GROUP BY group_id
UNION
SELECT MIN(id) FROM t WHERE status = 'available' GROUP BY group_id
)
I reworked the subquery into a UNION instead in this version, but the "AND" format would work just as well too. Also, if "code" was unique across the whole table, the NOT IN could be simplified down to excluding the group_id as well (though it would still be needed in the subqueries' GROUP BY clauses).
Edit: MySQL doesn't like subqueries referencing tables being UPDATEd/DELETEd in the WHERE of the query doing the UPDATE/DELETE; in those cases, you can usually double-wrap the subquery to give it an alias, causing MySQL to treat it as a temporary table (behind the scenes).
DELETE FROM t
WHERE t.status = 'available'
AND t.id NOT IN (
SELECT * FROM (
SELECT MAX(id) FROM t WHERE status = 'available' GROUP BY group_id
UNION
SELECT MIN(id) FROM t WHERE status = 'available' GROUP BY group_id
) AS a
)
Another alternative, I don't recall if MySQL complains as much about joins in DELETE/UPDATE....
DELETE t
FROM t
LEFT JOIN (
SELECT MIN(id) AS minId, MAX(id) AS maxId, 1 AS keep_flag
FROM t
WHERE status = 'available'
GROUP BY group_id
) AS tKeep ON t.id IN (tKeep.minId, tKeep.maxId)
WHERE t.status = 'available'
AND tKeep.keep_flag IS NULL
To keep the min and max ids, I think a join is the simplest solution:
DELETE t
FROM t LEFT JOIN
(SELECT group_id, MIN(id) as min_id, MAX(id) as max_id
FROM t
WHERE t.status = 'available'
GROUP BY group_id
) tt
ON t.id IN (tt.min_id, tt.max_id)
WHERE t.status = 'available' AND
tt.group_id IS NULL;
If the column "id" is the PRIMARY KEY or a UNIQUE KEY, then we could use a correlated subquery to get the second lowest value for a particular group_id.
We could then use that to identify rows for group_id that have higher values of the "id" column.
A query something like this:
SELECT t.`id`
, t.`group_id`
FROM `setup_like_this` t
WHERE t.`status` = 'available'
AND t.`id`
> ( SELECT s.`id`
FROM `setup_like_this` s
WHERE s.`status` = 'available'
AND s.`group_id` = t.`group_id`
ORDER
BY s.`id`
LIMIT 1,1
)
We test that as a SELECT first, to examine the rows that are returned. When we are satisfied this query is returning the set of rows we want to delete, we can replace SELECT ... FROM with DELETE t.* FROM to convert it to a DELETE statement to remove the rows.
Error 1093 encountered converting to DELETE statement.
One workaround is to make the query above into a inline view, and then join to the target table
DELETE q.*
FROM `setup_like_this` q
JOIN ( -- inline view, query from above returns `id` of rows we want to delete
SELECT t.`id`
, t.`group_id`
FROM `setup_like_this` t
WHERE t.`status` = 'available'
AND t.`id`
> ( SELECT s.`id`
FROM `setup_like_this` s
WHERE s.`status` = 'available'
AND s.`group_id` = t.`group_id`
ORDER
BY s.`id`
LIMIT 1,1
)
) r
ON r.id = q.id
select id, code, group_id, status
from (
select id, code, group_id, status
, ROW_NUMBER() OVER (
PARTITION BY group_id
ORDER BY id DESC) row_num
) rownum
from a
) q
where rownum < 3
I have a MySQL table tbl below:
now I run the following query:
SELECT DAY_NUMBER, WEEK_NUMBER, MAX(total_volume)
FROM `tbl`
GROUP BY WEEK_NUMBER
I get the following output:
Everything looks good except for the DAY_NUMBER. The DAY_NUMBER does not reflect the TOTAL_VOLUME from which I query the MAX(TOTAL_VOLUME). If you look at WEEK_NUMBER 31, the MAX(TOTAL_VOLUME) 777 has DAY_NUMBER 7 but the query has 5.
My goal is to have DAY_NUMBER reflect MAX(TOTAL_VOLUME) value DAY_NUMBER.
could you please tell me how do I fix it?
With NOT EXISTS:
SELECT t.*
FROM tbl t
WHERE NOT EXISTS (
SELECT 1 FROM tbl
WHERE WEEK_NUMBER = t.WEEK_NUMBER AND total_volume > t.total_volume
)
Use like this,
SELECT DAY_NUMBER, WEEK_NUMBER, total_volume
FROM `tbl` WHERE total_volume IN(SELECT MAX(total_volume)
FROM `tbl`
GROUP BY WEEK_NUMBER)
You will get Desired output
Do not use GROUP BY for a query where you should be filtering.
I recommend a correlated subquery:
select t.*
from tbl t
where t.total_volume = (select max(t2.total_volume)
from tbl t2
where t2.week_number = t.week_number
);
Alternatively, you can use window functions in MySQL 8+:
select t.*
from (select t.*,
row_number() over (partition by week_number order by volume desc) as seqnum
from tbl t
) t
where seqnum = 1;
With join
drop table if exists t;
create table t
(day_number int, week_number int, value int);
insert into t values
(1,1,10),(2,1,20),
(10,2,20),(11,2,10);
select t.day_number,t.week_number,t.value
from t
join
(select week_number,max(value) m
from t
group by week_number
) w on w.week_number = t.week_number and w.m = t.value;
+------------+-------------+-------+
| day_number | week_number | value |
+------------+-------------+-------+
| 2 | 1 | 20 |
| 10 | 2 | 20 |
+------------+-------------+-------+
2 rows in set (0.00 sec)
In the event of a draw you will get all days which match the max value.
I am using a MySQL query to fetch data from 2 tables. Here I have a status Transfer Out in table2. I do need to fetch all the details with status Transfer Out and at the same time, there should not be any details with Transfer In status which is added after the Transfer Out. So that I should not get the details which are Transfer back In after a Transfer Out.
Right now I am using subquery for the same. But when the data count gets higher, it is causing timeout issues. Is there a better way to rewrite the query and get the same result?
My query sample is
SELECT sq.etid
FROM (
SELECT og.etid, pt.timestamp
FROM og_membership og
INNER JOIN table1 n ON(n.nid=og.etid)
INNER JOIN table2 pt ON(og.etid=pt.animal_nid)
WHERE og.entity_type='node'
AND pt.partner_gid = :gid
AND pt.shelter_gid = :our_gid
AND pt.type = 'Transfer Out'
AND (
SELECT count(id)
FROM table2
WHERE timestamp > pt.timestamp
AND type = 'Transfer In'
AND partner_gid = :gid
AND shelter_gid = :our_gid
) = 0
) AS sq
You could possibly do this with a group by for example
select something
from somehwere
group by something having isnull(max(out_date),0) > isnull(max(indate) ,0)
For example
DROP TABLE IF EXISTS LOANS;
CREATE TABLE LOANS (ID INT AUTO_INCREMENT PRIMARY KEY, ISBN INT,DIRECTION VARCHAR(3), DT DATETIME);
INSERT INTO LOANS(ISBN,DIRECTION,DT) VALUES
(1,'OUT','2017-10-01 09:00:00'),
(2,'OUT','2017-10-02 10:00:00'),
(2,'IN', '2017-10-02 10:10:00'),
(3,'REC','2017-10-02 10:00:00'),
(4,'REC','2017-10-02 10:00:00'),
(4,'OUT','2017-10-03 10:00:00'),
(4,'IN', '2017-10-04 10:00:00'),
(4,'OUT','2017-10-05 10:00:00')
;
SELECT ISBN
FROM LOANS
WHERE DIRECTION IN('OUT','IN')
GROUP BY ISBN HAVING
MAX(CASE WHEN DIRECTION = 'OUT' THEN DT ELSE 0 END) >
MAX(CASE WHEN DIRECTION = 'IN' THEN DT ELSE 0 END) ;
result
+------+
| ISBN |
+------+
| 1 |
| 4 |
+------+
2 rows in set (0.00 sec)
In case of a tie on DT you could substitute id.
Change
( SELECT COUNT(id) FROM ... ) = 0
to
EXISTS ( SELECT 1 FROM ... )
Get rid of the outermost query and the first pt.timestamp. (Or is there some obscure reason for pt.timestamp?)
table2 needs INDEX(type, partner_gid, shelter_gid, timestamp). timestamp must be last, but the others can be in any order.
table2 needs INDEX(type, partner_gid, shelter_gid, animal_nid); the columns can be in any order. (This index cannot be combined with the previous one.)
og_membership needs INDEX(etid, entity_type) (in either order).
Why do you have INNER JOIN table1 n ON(n.nid=og.etid) in the query? table1 does not seem to be used at all -- except maybe for verifying the existence of a row. Remove it if possible.
After making changes, please provide EXPLAIN SELECT ... and SHOW CREATE TABLE for the 2 (or 3??) tables.
I'd like to select all the rows from a temporary table that have a value equal to the maximum value.
TEMPORARY TABLE test
id | value
1 | 7
2 | 6
3 | 7
Expected result:
id | value
1 | 7
3 | 7
I've already tried several things but all attempts (except creating another temporary table with the same content) failed so far because of "You cannot refer to a TEMPORARY table more than once in the same query." (Source: http://dev.mysql.com/doc/refman/5.0/en/temporary-table-problems.html).
Is there a possibility to do this in a more "elegant" way than copying the table and its contents?
What I've tested so far:
SELECT table1.* FROM test table1 LEFT JOIN test table2 ON table1.value < table2.value
WHERE table2.value IS NULL;
SELECT * FROM test WHERE value = (SELECT MAX(value) FROM test);
And this is my current solution:
CREATE TEMPORARY TABLE test2 (...);
INSERT INTO test2 SELECT * FROM test;
SELECT * FROM test WHERE value = (SELECT MAX(value) FROM test2);
You could try using variables. The following will scan the test table only once (not-tested):
SELECT test.*,
#curMax := IF(#curMax = -1, value, #curMax)
FROM test,
(SELECT #curMax := -1) r
HAVING #curMax = value OR #curMax = -1
ORDER BY value DESC;
Select id,value From SomeTable
inner Join (Select Max(SomeValue) as MaximumValue From SomeTable) maximums
On SomeTable.Value = maximums.MaximumValue
Should do the job
How about this:
SELECT MAX(value) INTO #max
FROM test;
SELECT *
FROM test
WHERE value = #max;