Can anyone give me some pointers to get this working??
I want to combine to queries into one listing with different sorting.
The first will be any business that are a spotlight sorted randomly, then all other listings sorted alphabetically.
This is what I'm using, but the sorting doesn't work.
(SELECT * FROM business_listings WHERE city='Toronto' AND spotlight='1' ORDER by rand())
UNION
(SELECT * FROM business_listings WHERE city='Toronto' AND spotlight='0' ORDER BY busname)
You may not need a UNION, use the CASE clause in ORDER BY like this:
SELECT *
FROM business_listings
WHERE city='Toronto'
ORDER BY CASE
WHEN spotlight='1' THEN FLOOR(RAND()*10)
WHEN spotlight='0' THEN 10
END, busname
What it will do is, sort records using a random value (from 0 to 9) for records having spotlight=1. Whereas all records having spotlight=0 will come later because ORDER BY will use the value 10 as the sort order.
Working Demo: http://sqlfiddle.com/#!2/1bf6e/1
from this SO question
Example Fiddle
Try this:
SELECT *
FROM (SELECT *
FROM business_listings
WHERE city='Toronto'
AND spotlight='1'
ORDER by rand()) as t1
UNION ALL
SELECT *
FROM (SELECT *
FROM business_listings
WHERE city='Toronto'
AND spotlight='0'
ORDER BY busname) as t2
Related
I want to select all the matching results in a database table with also random results but with the matching results being at the top. With the way, I am doing now I am using two queries first one being the matching query, and if the count is zero I now select random results. I would like to do this with just one query.
You could attempt using a UNION ALL query as follows.
select product_name,price
from marketing_table
where price >=5000 /*user supplied filter*/
and price <=10000 /*user supplied filter*/
union all
select m.product_name,m.price
from marketing_table m
where not exists (select *
from marketing_table m1
where m1.price >=5000 /*user supplied filter*/
and m1.price <=10000 /*user supplied filter*/
)
What I understand from you comment, you may try something simple like this first:
SET #product := 'purse'; -- search term
SELECT * FROM product
ORDER BY product_name LIKE CONCAT('%',#product,'%') DESC, price ASC;
This is the simplest I can think of and it could be a starting point for you.
Here's a demo : https://www.db-fiddle.com/f/31jrR27dFJqYQQigzBqLcs/2
If this is not what you want, you have to edit your question and insert some example data with expected output. Your current question tend to be flagged as too broad and need focus/clarity.
Did you try using a UNION subquery with a LIMIT?
SELECT *
FROM (
SELECT 0 priority, t.*
FROM first_table t
UNION ALL
SELECT 1 priority, t.*
FROM second_table t
)
ORDER BY priority
LIMIT 20
If you do not want to include any second_table records if first_table returns, you would need to do a subquery on the second query to confirm that no rows exist.
SELECT *
FROM (
SELECT 0 priority, t.*
FROM first_table t
UNION ALL
SELECT 1 priority, t.*
FROM second_table t
LEFT JOIN (SELECT ... FROM first_table) a
WHERE a.id IS NULL
)
ORDER BY priority
LIMIT 20
I think it would be possible to use the Common Table Expressions (CTE) feature in MySQL 8, if you are using that version.
https://dev.mysql.com/doc/refman/8.0/en/with.html
I am trying to get my head around using GROUP_CONCAT within MYSQL.
Basically I have the following table, table1:
id, field1, field2, active
I want to bring back 5 rows within the table but in random order. So I'm using this:
SELECT GROUP_CONCAT(id ORDER BY rand()) FROM table1 WHERE active=1
This behaves as I would expect. I then want to use the output to select the other columns (field1, field2) from the table and display the results.
So I've tried using:
SELECT *
FROM table1
WHERE id IN
(
SELECT GROUP_CONCAT(id ORDER BY rand()) as id FROM table1 WHERE active=1
);
I expected something like the above to work but I cant figure out why it doesn't. It DOES bring back results but not all of them, (i.e.) my table contains 10 rows. 6 rows are set to active=1. Therefore I would expect 6 rows to be returned ... this isn't happening I may get 1,2 or 0.
Additionally if it helps I'd like to limit the number of results returned by the sub-query to 3 but adding LIMIT doesn't seem to have any affect on the results returned.
Thank you in advance for your help
I think this is what you are looking for. This will bring back 5 random active rows.
SELECT *
FROM table1
WHERE active=1
ORDER BY RAND()
LIMIT 5;
why not use this :
SELECT *, GROUP_CONCAT(id ORDER BY rand()) as randoms FROM table1 WHERE active=1
If I understand correctly, you are trying to build a query like this:
select *
from table1
where id in (1,2,3,4,5) -- Just an example
and you are trying to "fill" the in condition with a group_concat() result.
That's not the way to do it.
You only need to specify the subquery in the parenthesis:
select *
from table1
where id in (select id from table1 where active=1)
Notice some additional things:
The order by rand() is irrelevant, because the in () will be evaluated regardless of the order of the values.
In this particular scenario, I would recommend to use a join instead of in.
Using join:
select t1.*
from
table1 as t1
inner join table1 as t2 on t1.id = t2.id
where t2.active=1
It is not clear to me where a LIMIT applies to a UNION
If I have:
SELECT * From table A
where conditions
UNION
SELECT * From table B
where conditions
LIMIT 10
Does the LIMIT 10 apply to the result of the UNION? Or to the select of table B?
What I need is to apply to the result of the UNION
Where is the UNION operator? Anyway the LIMIT of 10 probably applies on the result of the UNION at least in the place you put it.
Straight from the manual:
To use an ORDER BY or LIMIT clause to sort or limit the entire UNION result, parenthesize the individual SELECT statements and place the ORDER BY or LIMIT after the last one. The following example uses both clauses:
(SELECT a FROM t1 WHERE a=10 AND B=1)
UNION
(SELECT a FROM t2 WHERE a=11 AND B=2)
ORDER BY a LIMIT 10;
A statement without parentheses is equivalent to one parenthesized as just shown.
In your case:
SELECT * From table A
where conditions
UNION --assuming the union is here
SELECT * From table B
where conditions
LIMIT 10
The limit will be applied to the result of the union.
Assuming table1 and table2 both have a large number of rows (ie several hundred thousand), is the following an inefficient query?
Edit: Order by field added.
SELECT * FROM (
SELECT title, updated FROM table1
UNION
SELECT title, updated FROM table2
) AS query
ORDER BY updated DESC
LIMIT 25
If you absolutely need distinct results, another possibility is to use union all and a group by clause instead:
SELECT title FROM (
SELECT title FROM table1 group by title
UNION ALL
SELECT title FROM table2 group by title
) AS query
group by title
LIMIT 25;
Testing this without the limit clause on an indexed ID column from two tables with ~920K rows each in a test database (at $work) resulted in a bit over a second with the query above and about 17 seconds via a union.
this should be even faster - but then I see no ORDER BY so what 25 records do you actually want?
SELECT * FROM (
SELECT title FROM table1 LIMIT 25
UNION
SELECT title FROM table2 LIMIT 25
) AS query
LIMIT 25
UNION must make an extra pass to fetch the distinct records, so you should use UNION ALL.
Yes, use order by and limits in the inner queries.
SELECT * FROM (
(SELECT title FROM table1 ORDER BY title ASC LIMIT C)
UNION
(SELECT title FROM table2 ORDER BY title ASC LIMIT C)
) AS query
LIMIT 25
This will only go through C rows instead of N (hundreds of thousands). The ORDER BY is necessary and should be on an indexed column.
C is a heuristic constant that should be tuned according to the domain. If you only expect a few duplicates, C=50-100 is probably ok.
You can also find out this for yourself by using EXPLAIN.
I'am trying to understand what causes the following, maybe you could help me:
I have a query like:
select field1,fieldDate from table1
union all
select field1,fieldDate from table2
order by fieldDate desc
and the another one like this:
select field1,field2,fieldDate from table1
union all
select field1,field2,fieldDate from table2
order by fieldDate desc
So basically they are the same with the exception that in the second I retrieve an extra field.
Now, both results come with a diferent ordering, but just for the cases that the dates are exacly the same. For example there are 2 rows (row1,row2) with date 2009-11-25 09:41:55. For query 1 row1 comes before row2 and for query 2 row2 comes before row1.
Does somebody knows why this happens?
Thanks,
Regards
The ordering based on any fields that you don't explicitly order by is undefined, and the optimizer can change the ordering if it thinks that results in a better execution plan. Given two rows with the exact same value in the order by field you can not depend on them being in any particularly order in relation to each other unless you explicitly order by another field with different values.
Can you do this
select * from ( select
field1,field2,fieldDate, 0 as ordercol from table1
union all select
field1,field2,fieldDate, 1 as ordercol from table2) t1
order by fieldDate desc, ordercol asc
Straight from the MySQl manual, to user order by on a union you have to parenthesis the individual tables.
(select field1,fieldDate from table1)
union all
(select field1,fieldDate from table2)
order by fieldDate desc
This is not SQL standards compliant! The code you entered should order the union of both tables but to my surprise MySQL has the above syntax.
The order in which rows with the same fieldDate are returned can differ for each query execution. Usually this order will be the same but you should not count on it. If you want any extra ordering state more order by fields.
EDIT: This answer is wrong: the order by works on the entire union. I'll leave it here to save others the trouble :)
Your order by only works on the second part of the union. You can use a subquery to make the order by work on the entire union:
select field1,field2,fieldDate
from (
select field1,field2,fieldDate
from table1
union all
select field1,field2,fieldDate
from table2
) SubQueryName
order by fieldDate desc