How can I optimize this query SQL?
CREATE TABLE table1 AS
SELECT * FROM temp
WHERE Birth_Place IN
(SELECT c.DES_COM
FROM tableCom AS c
WHERE c.COD_PROV IS NULL)
ORDER BY Cod, Birth_Date
I think that the problem is the IN clause
First of all it's not quite valid SQL, since you are selecting and sorting by columns that are not part of the group. What you want to do is called "select top N in group", check out Select first row in each GROUP BY group?
Your query doesn't make sense, because you have SELECT * with GROUP BY. Ignoring that, I would recommend writing the query as:
SELECT t.*
FROM temp t
WHERE EXISTS (SELECT 1
FROM tableCom c
WHERE t.Birth_Place = c.DES_COM AND
c.COD_PROV IS NULL
)
ORDER BY Cod, Birth_Date;
For this, I recommend an index on tableCom(desc_com, cod_prov). Your database might also be able to use an an index on temp(cod, birth_date, birthplace).
Related
My problem is the following, I want set a list of ID in a variable, then use this variable in a subquery. The problem is that WorkBench (my GUI) return the following error : "subquery returning multiple rows". It seems to me that's what I want.
Please explain me where I am wrong.
This is my query :
set #listID := (select ID_VOIE as ID from voies
where ORIGINE = 'XXX'
group by CODE_INSEE, CODE_VOIE
having count(*) > 1);
select substring(v.CODE_INSEE,1,2), count(*) from voies v
where v.ID_VOIE in (#listID)
group by substring(vs.CODE_INSEE,1,2);
The thing is I'm blocked with the "group by", I want do a groupd by after a first group by, that's why I can't (or at least i didn't find a way) write the request with a single WHERE clause.
The thing is I know that I can put the whole request directly in my subquery instead of using variable but :
It can let me use this trick in another requests that needed this behaviour (DRY concept !)
I'm not sure but the subquery will be executed in each turn of my loop, and that will be very inefficient
So I seek 2 possible ways : a way that let me use a list in a variable in a subquery OR a way that let me use "group by" twice in a single query.
Thanks you in advance for your answers (oh and sorry for my english, this is not my maternal language).
Unless you need that variable for something else, you should be able to skip it entirely as follows:
SELECT
SUBSTRING(v.CODE_INSEE,1,2),
COUNT(*)
FROM
voies v
WHERE
v.ID_VOIE in
(SELECT
ID_VOIE as ID
FROM
voies
WHERE
ORIGINE = 'XXX'
GROUP BY
CODE_INSEE,
CODE_VOIE
HAVING COUNT(*) > 1)
GROUP BY
SUBSTRING(vs.CODE_INSEE,1,2);
As you say, the subquery will be executed for all rows. To avoid that, a variable would be best, but MySQL doesn't support table variables. Instead, you can use a temporary table:
IF EXISTS DROP TABLE myTempTable;
CREATE TEMPORARY TABLE myTempTable (ID_VOIE int); -- I don't know the datatype
INSERT INTO myTempTable (ID_VOIE)
SELECT DISTINCT -- using distinct so I can join instead of use IN.
ID_VOIE as ID from voies
WHERE
ORIGINE = 'XXX'
GROUP BY
CODE_INSEE, CODE_VOIE
HAVING COUNT(*) > 1
And now you can do this:
SELECT
SUBSTRING(v.CODE_INSEE,1,2), COUNT(*)
FROM
voies v
JOIN myTempTable tt ON
v.ID_VOIE = tt.ID_VOIE
GROUP BY SUBSTRING(vs.CODE_INSEE,1,2);
I have the below SQL statement and I am trying to add a USE INDEX clause to index on percent and doc_type which I have already added. No matter where I put the USE INDEX (ipercent,idoc_type) clause, it gives me an error say USE is in the wrong place. Any ideas?
select name,e_title
from
(select * from problem2.workson natural join
(problem2.documents,problem2.employees)) as newTable
where percent = 100
and (doc_type = 'internal-report'
or doc_type = 'external-report')
group by name
having count(name) > 1
Explain output:
I'm not an expert in SQL, i have an sql statement :
SELECT * FROM articles WHERE article_id IN
(SELECT distinct(content_id) FROM contents_by_cats WHERE cat_id='$cat')
AND permission='true' AND date <= '$now_date_time' ORDER BY date DESC;
Table contents_by_cats has 11000 rows.
Table articles has 2700 rows.
Variables $now_date_time and $cat are php variables.
This query takes about 10 seconds to return the values (i think because it has nested SELECT statements) , and 10 seconds is a big amount of time.
How can i achieve this in another way ? (Views or JOIN) ?
I think JOIN will help me here but i don't know how to use it properly for the SQL statement that i mentioned.
Thanks in advance.
A JOIN is exactly what you are looking for. Try something like this:
SELECT DISTINCT articles.*
FROM articles
JOIN contents_by_cats ON articles.article_id = contents_by_cats.content_id
WHERE contents_by_cats.cat_id='$cat'
AND articles.permission='true'
AND articles.date <= '$now_date_time'
ORDER BY date DESC;
If your query is still not as fast as you would like then check that you have an index on articles.article_id and contents_by_cats.content_id and contents_by_cats.cat_id. Depending on the data you may want an index on articles.date as well.
Do note that if the $cat and $now_date_time values are coming from a user then you should really be preparing and binding the query rather than just dumping these values into the query.
This is the query we are starting with:
SELECT a.*
FROM articles a
WHERE article_id IN (SELECT distinct(content_id)
FROM contents_by_cats
WHERE cat_id ='$cat'
) AND
permission ='true' AND
date <= '$now_date_time'
ORDER BY date DESC;
Two things will help this query. The first is to rewrite it using exists rather than in and to simplify the subquery:
SELECT a.*
FROM articles a
WHERE EXISTS (SELECT 1
FROM contents_by_cats cbc
WHERE cbc.content_id = a.article_id and cat_id = '$cat'
) AND
permission ='true' AND
date <= '$now_date_time'
ORDER BY date DESC;
Second, you want indexes on both articles and contents_by_cats:
create index idx_articles_3 on articles(permission, date, article_id);
create index idx_contents_by_cats_2 on contents_by_cat(content_id, cat_id);
By the way, instead of $now_date_time, you can just use the now() function in MySQL.
I have a list of ids, and I want to query a mysql table for ids not present in the table.
e.g.
list_of_ids = [1,2,4]
mysql table
id
1
3
5
6
..
Query should return [2,4] because those are the ids not in the table
since we cant view ur code i can only work on asumption
Try this anyway
SELECT id FROM list_of_ids
WHERE id NOT IN (SELECT id
FROM table)
I hope this helps
There is a horrible text-based hack:
SELECT
substr(result,2,length(result)-2) AS notmatched
FROM (
SELECT
#set:=replace(#set,concat(',',id,','),',') AS result
FROM (
select #set:=concat(',',
'1,2,4' -- your list here
,',')
) AS setinit,
tablename --Your tablename here
) AS innerview
ORDER BY LENGTH(result)
LIMIT 1;
If you represent your ids as a derived table, then you can do this directly in SQL:
select list.val
from (select 1 as val union all
select 2 union all
select 4
) list left outer join
t
on t.id = list.val
where t.id is null;
SQL doesn't really have a "list" type, so your question is ambiguous. If you mean a comma separated string, then a text hack might work. If you mean a table, then something like this might work. If you are constructing the SQL statement, I would advise you to go down this route, because it should be more efficient.
I have this query:
select *
from transaction_batch
where id IN
(
select MAX(id) as id
from transaction_batch
where status_id IN (1,2)
group by status_id
);
The inner query runs very fast (less than 0.1 seconds) to get two ID's, one for status 1, one for status 2, then it selects based on primary key so it is indexed. The explain query says that it's searching 135k rows using where only, and I cannot for the life of me figure out why this is so slow.
The inner query is run seperatly for every row of your table over and over again.
As there is no reference to the outer query in the inner query, I suggest you split those two queries and just insert the results of the inner query in the WHERE clause.
select b.*
from transaction_batch b
inner join (
select max(id) as id
from transaction_batch
where status_id in (1, 2)
group by status_id
) bm on b.id = bm.id
my first post here.. sorry about the lack of formatting
I had a performance problem shown below:
90sec: WHERE [Column] LIKE (Select [Value] From [Table]) //Dynamic, slow
1sec: WHERE [Column] LIKE ('A','B','C') //Hardcoded, fast
1sec: WHERE #CSV like CONCAT('%',[Column],'%') //Solution, below
I had tried joining rather than subquerying.
I had also tried a hardcoded CTE.
I had lastly tried a temp table.
None of these standard options worked, and I was not willing to dosp_execute option.
The only solution that worked as:
DECLARE #CSV nvarchar(max) = Select STRING_AGG([Value],',') From [Table];
// This yields #CSV = 'A,B,C'
...
WHERE #CSV LIKE CONCAT('%',[Column],'%')