I have one table with user and their posts. It looks like "user_id | post_id | post_status".
Now I have a list of userid (ex, 100 users) and I want to know how many of them has at least one post that gets deleted (ex, post_status 3).
Here is my sample search:
select count(distinct user_id)
from post_table
where user_id in ( {my set} )
and post_status=3
It runs super slow since it iterates the entire table. Is there a way to speed up the query?
Use something like
SELECT COUNT(*)
FROM
-- the list of userid as a rowset
( SELECT 123 AS user_id UNION ALL
SELECT 456 UNION ALL
-- ...
SELECT 789
) user_id_list
WHERE EXISTS ( SELECT NULL
FROM post_table
WHERE post_table.user_id = user_id_list.user_id
AND post_table.post_status = 3 )
If your MySQL version is 8.0.4 or above then you may provide the users list as CSV/JSON and parse it using JSON_TABLE (the query text will be more compact).
INDEX(post_status, user_id)
may help speed up your query, especially if very few rows have status=3.
This could also speed up Akina's solution.
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).
I'm trying to select 2 different columns (newsID from the table news and movID from the table movies) so that I can use mysql_num_rows to grab the items in those conditions.
I tried this with the code below, but it is not working. How can I fix it?
$queryy="SELECT newsID FROM ".PREFIX."news WHERE published='1'";
$queryy="UNION (SELECT movID FROM ".PREFIX."movies WHERE activated='2')";
$all=safe_query($queryy);
$gesamt=mysql_num_rows($all);
You're overwriting the variable with the second assignment. Do it all in one string assignment:
$queryy = "SELECT newsID FROM ".PREFIX."news WHERE published='1'
UNION (SELECT movID FROM ".PREFIX."movies WHERE activated='2')";
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],'%')
I'd like to use a single SQL query (in MySQL) to find the record which comes after one that I specify.
I.e., if the table has:
id, fruit
-- -----
1 apples
2 pears
3 oranges
I'd like to be able to do a query like:
SELECT * FROM table where previous_record has id=1 order by id;
(clearly that's not real SQL syntax, I'm just using pseudo-SQL to illustrate what I'm trying to achieve)
which would return:
2, pears
My current solution is just to fetch all the records, and look through them in PHP, but that's slower than I'd like. Is there a quicker way to do it?
I'd be happy with something that returned two rows -- i.e. the one with the specified value and the following row.
EDIT: Sorry, my question was badly worded. Unfortunately, my definition of "next" is not based on ID, but on alphabetical order of fruit name. Hence, my example above is wrong, and should return oranges, as it comes alphabetically next after apples. Is there a way to do the comparison on strings instead of ids?
After the question's edit and the simplification below, we can change it to
SELECT id FROM table WHERE fruit > 'apples' ORDER BY fruit LIMIT 1
SELECT * FROM table WHERE id > 1 ORDER BY id LIMIT 1
Even simpler
UPDATE:
SELECT * FROM table WHERE fruit > 'apples' ORDER BY fruit LIMIT 1
So simple, and no gymnastics required
Select * from Table
where id =
(Select Max(id) from Table
where id < #Id)
or, based on the string #fruitName = 'apples', or 'oranges' etc...
Select * from Table
where id =
(Select Max(id) from Table
where id < (Select id from Table
Where fruit = #fruitName))
I'm not familiar with the MySQL syntax, but with SQL Server you can do something with "top", for example:
SELECT TOP 1 * FROM table WHERE id > 1 ORDER BY id;
This assumes that the id field is unique. If it is not unique (say, a foreign key), you can do something similar and then join back against the same table.
Since I don't use MySQL, I am not sure of the syntax, but would imagine it to be similar.
Unless you specify a sort order, I don't believe the concepts of "previous" or "next" are available to you in SQL. You aren't guaranteed a particular order by the RDBMS by default. If you can sort by some column into ascending or descending order that's another matter.
This should work. The string 'apples' will need to be a parameter.
Fill in that parameter with a string, and this query will return the entire record for the first fruit after that item, in alphabetical order.
Unlike the LIMIT 1 approach, this should be platform-independent.
--STEP THREE: Get the full record w/the ID we found in step 2
select *
from
fruits fr
,(
--STEP TWO: Get the ID # of the name we found in step 1
select
min(vendor_id) min_id
from
fruits fr1
,(
--STEP ONE: Get the next name after "apples"
select min(name) next_name
from fruits frx
where frx.name > 'apples'
) minval
where fr1.name = minval.next_name
) x
where fr.vendor_id = x.min_id;
The equivalent to the LIMIT 1 approach in Oracle (just for reference) would be this:
select *
from
(
select *
from fruits frx
where frx.name > 'apples'
order by name
)
where rownum = 1
I don't know MySQL SQL but I still try
select n.id
from fruit n
, fruit p
where n.id = p.id + 1;
edit:
select n.id, n.fruitname
from fruits n
, fruits p
where n.id = p.id + 1;
edit two:
Jason Lepack has said that that doesn't work when there are gaps and that is true and I should read the question better.
I should have used analytics to sort the results on fruitname
select id
, fruitname
, lead(id) over (order by fruitname) id_next
, lead(fruitname) over (order by fruitname) fruitname_next
from fruits;
If you are using MS SQL Server 2008 (not sure if available for previous versions)...
In the event that you are trying to find the next record and you do not have a unique ID to reference in an applicable manner, try using ROW_NUMBER(). See this link
Depending on how savvy your T-SQL skill is, you can create row numbers based on your sorting order. Then you can find more than just the previous and next record. Utilize it in views or sub-queries to find another record relative to the current record's row number.
SELECT cur.id as id, nxt.id as nextId, prev.id as prevId FROM video as cur
LEFT JOIN video as nxt ON nxt.id > cur.id
LEFT JOIN video as prev ON prev.id < cur.id
WHERE cur.id = 12
ORDER BY prev.id DESC, nxt.id ASC
LIMIT 1
If you want the item with previous and next item this query lets you do just that.
This also allows You to have gaps in the data!
How about this:
Select * from table where id = 1 + 1