How would you optimize the following query?
'example_companies' contains companies data.
'example_roles_companies' contains companies roles (pivot)
'example_industries_companies' contains companies industries (pivot)
SELECT DISTINCT a.id,
a.mode,
a.name,
a.city,
b.name AS USER,
b.phone
FROM example_companies a
LEFT JOIN example_users b
ON a.contact_id = b.id
LEFT JOIN example_roles_companies c
ON a.id = c.company_id
WHERE "2" IN (SELECT industry_id
FROM example_industries_companies
WHERE company_id = a.id)
AND c.role_id = 2
AND a.account_mode != 2
ORDER BY a.id
Query:
SELECT DISTINCT a.id,
a.mode,
a.name,
a.city,
b.name AS USER,
b.phone
FROM example_companies a
LEFT JOIN example_users b ON a.contact_id = b.id
INNER JOIN example_roles_companies c ON a.id = c.company_id AND c.role_id = 2
INNER JOIN example_industries_companies i
ON i.company_id = a.id AND i.industry_id = "2"
WHERE
a.account_mode != 2
ORDER BY
a.id
Structure:
Index on a.id, not null
Index on b.id, not null [analyze the opportunity of adding another index (b.id, b.name, b.phone) to this table as well]
Index on (c.company_id, c.role_id) not null both
Index on (i.company_id, i.industry_id), not null both
Remarks:
Please note that your industry_id = "2" seems weird to me, ids are generally numbers and if they are not then it should be looked since integers are faster to process than strings. Additionally, this way of double-quoting is not usual in mysql. Are you sure of your syntax?
Related
tables and query are here
http://sqlfiddle.com/#!9/2b6f35a/1/0
In it for each name i get its tags title, So it would be like this
name1: title1;
name2: title1;
name3: title1;
My problem is that i get double the tags
name1: title1, title1;
name2: title1, title1;
name3: title1;
What is the mistake i've made?
The entire problem comes for tablx
Sorry about the mess before, didn't know about sqlfiddle
The join with X table is returning the 4th row. http://sqlfiddle.com/#!9/2b6f35a/6, which draws the same title1 value in from the tags table, which is then aggregated into the final response with GROUP_CONCAT()
A solution if you need to join both these tables in one query but only want the title1 one time is to remove the GROUP_CONCAT() aggregator: http://sqlfiddle.com/#!9/2b6f35a/7
SELECT a.name, x.rate, c.title
FROM tabl1 a
LEFT JOIN tablx x ON x.pid = a.id
INNER JOIN tabl2 b ON a.id = b.pid
INNER JOIN tabl3 c ON c.id = b.bid
WHERE c.title IN ('title1')
GROUP BY a.id
In your case, it might be more useful to have an aggregator on the rate column for x table, like so: http://sqlfiddle.com/#!9/2b6f35a/9
SELECT a.name, x.rate, c.title, SUM(x.rate) AS rate_sum
FROM tabl1 a
LEFT JOIN tablx x ON x.pid = a.id
INNER JOIN tabl2 b ON a.id = b.pid
INNER JOIN tabl3 c ON c.id = b.bid
WHERE c.title IN ('title1')
GROUP BY a.id
If you just want to count the number of distinct tags in this situation, you can use COUNT(DISTINCT...). http://sqlfiddle.com/#!9/2b6f35a/15:
SELECT a.name, b.id as bid, c.title, x.id as xid, x.rate, c.title, SUM(x.rate) AS rate_sum, COUNT(DISTINCT c.title) as title_count
FROM tabl1 a
LEFT JOIN tablx x ON x.pid = a.id
INNER JOIN tabl2 b ON a.id = b.pid
INNER JOIN tabl3 c ON c.id = b.bid
WHERE c.title IN ('title1')
GROUP BY a.id
If everything in the posted question is correct, you aren't doing anything wrong.
See this sqlfiddle:
http://sqlfiddle.com/#!9/03205d/1
I have a big multiple table query join select where some values are optional.
This is the query:
SELECT a.date_in, a.date_out, b.name, b.phone, b.birthdate,
b.country, b.hotel, b.room_nr, b.passport_nr, c.email,
d.size, e.name, GROUP_CONCAT(DISTINCT g.service), GROUP_CONCAT(DISTINCT h.service)
, GROUP_CONCAT(DISTINCT i.time), GROUP_CONCAT(DISTINCT j.location)
FROM reservation a, rider b, user c,
bike_size d, bike e, services_reservation f, services g,
bike_shipping h, bike_shipping_reservation i
, bike_shipping_location j WHERE a.rider_id = b.id
AND b.user_id = c.id AND a.bike_size_id = d.id AND
d.bike_id = e.id AND a.id = f.reservation_id AND
f.services_id = g.id
AND h.id = i.bike_shipping_id AND a.id = i.reservation_id
AND i.bike_shipping_location_id = j.id
AND a.id = 80
In the tables from the query above, the table named services_reservation with the following columns (id, services_id, reservation_id) is completely empty in this case, which makes the values that I select from the table bike_shipping_reservation NULL.
How can I make some tables that I select from optional in case they are empty?
Here is the SQL Fiddle with 1 empty table, you can see the NULL results at the end (only GROUP_CONCAT(DISTINCT g.service) should be NULL).
http://sqlfiddle.com/#!9/ee31b/6
Here is the SQL Fiddle with all tables having values in there columns, you can see that all values are returned not NULL.
http://sqlfiddle.com/#!9/8bc033/34
Any thoughts?
Use left join where the table (or the row) are empty on don't match
SELECT a.date_in, a.date_out, b.name, b.phone, b.birthdate,
b.country, b.hotel, b.room_nr, b.passport_nr, c.email,
d.size, e.name, GROUP_CONCAT(DISTINCT g.service), GROUP_CONCAT(DISTINCT h.service)
, GROUP_CONCAT(DISTINCT i.time), GROUP_CONCAT(DISTINCT j.location)
FROM reservation a
INNER JOIN rider b on a.rider_id = b.id
INNER JOIN user c on b.user_id = c.id
INNER JOIN bike_size d on a.bike_size_id = d.id
INNER JOIN bike e ON d.bike_id = e.id
LEFT JOIN services_reservation f on a.id = f.reservation_id
INNER JOIN services g on f.services_id = g.id
INNER JOIN bike_shipping_reservation i on a.id = i.reservation_id
INNER JOIN bike_shipping h ON h.id = i.bike_shipping_id
INNER JOIN bike_shipping_location j on i.bike_shipping_location_id = j.id
where a.id = 80
i have 2 sql statements which produce the same result, but wondering which one to choose?
lets say 1 have 3 tables:
supplier
supplier_status
supplier_contact
statement 1)
SELECT a.*, b.status_name
(SELECT c.name FROM contact c
WHERE c.supplier_id = a.supplier_id
ORDER BY c.contact_id DESC limit 1) AS contact_name
FROM supplier a LEFT JOIN supplier_status b
ON a.status_id = b.status_id
statement 2)
SELECT a.*, b.status_name, c.name AS contact_name
FROM supplier a LEFT JOIN supplier_status b
ON a.status_id = b.status_id
LEFT JOIN (SELECT name, supplier_id
FROM contact
ORDER BY contact_id DESC
) c ON a.supplier_id = c.supplier_id
GROUP BY a.supplier_id
Try this query:
SELECT a.*, b.status_name, c.name AS contact_name
FROM supplier a
LEFT JOIN supplier_status b ON a.status_id = b.status_id
LEFT JOIN contact c ON a.supplier_id = c.supplier_id
LEFT JOIN contact d ON c.supplier_id = d.supplier_id AND c.contact_id < d.contact_id
WHERE d.contact_id IS NULL
It's possible that it doesn't produce the same result as yours (I didn't test it) but if it does then all you have to do is to make sure the fields that appear in the JOIN conditions are indexed (they probably are FKs, so they already are).
I'm not that into MySQL joins, so maybe you could give me a hand. I've got the following tables:
Table a
Fields ID,name
Table b
Fields aID,cID,ID,found
Table c
Fields ID,name
The result I want to get is the following: I want all the records where b.found = 1. Of these records I don't want a.id or a.name, but I want the number of records that would have been returned if I would have wanted so. So if there are five records that have b.found = 1 and c.id = (for example) 3, then I want a returned value of 5, c.id and c.name.
Someone is able to do this?
Actually this is what I want to get from the database:
A list of all records in table C and a count of records in table B that has found = 1 and b.c_id = c.id
Table: a
Fields: ID, name
Table: b
Fields: aID, cID, found
Table: c
Fields: ID, name
SELECT c.ID, c.name, COUNT(1)
FROM b
JOIN c ON c.ID = b.cID AND b.found=1
GROUP BY c.ID
SELECT c.id, c.name, COUNT(*)
FROM c
INNER JOIN b
ON c.id = b.c_id
AND b.found = 1
GROUP BY c.id, c.name
SELECT COUNT(*), c.id, c.name
FROM a, b, c
WHERE a.id = b.a.id AND c.id = b.a.id AND b.found = 1 AND c.id = idThatIAmSearchingFor
Apologies if I didn't get the syntax exact, but I believe that's the basic structure you want. The COUNT function returns the number of rows found by the query.
Something like:
SELECT count(`c`.*),
`c`.`id`,
`c`.`name`
FROM `b`
JOIN `c`
ON `c`.`id` = `b`.`c_id`
WHERE `b.found` = 1
I think this would provide the required output -
select count(*), b.cID, c.name from b
inner join c on c.id=b.cID and b.found=1
group by b.cID
SELECT COUNT(*) AS Count, c.id, c.name
FROM b join a on a.id = b.a_id
WHERE b.found = 1
GROUP BY c.Id;
COUNT returns count of records in each group from GROUP BY.
This is the query I'm performing (without some Joins that are not relevant):
SELECT a.*, c.id
FROM a
LEFT OUTER JOIN b ON a.id = b.id_anunciante
LEFT OUTER JOIN c ON c.id = b.id_rubro
GROUP BY a.id
Each row of "a" is linked with 1 to 5 rows in "b".
The problem is that GROUP BY has performance issues (it takes 10x or more using GROUP BY than not using it). I need to retrieve only one row of each member in "a".
How can I make this faster?
edit: I need to be able to filter by a.id AND/OR c.id. The resultset I should be getting is only 1 row per "valid" member of "a", meaning the rows that match the constraints. Rows that don't match the filters shouldn't be returned.
In my original query, this would be done this way:
SELECT a.*, c.id
FROM a
LEFT OUTER JOIN b ON a.id = b.id_anunciante
LEFT OUTER JOIN c ON c.id = b.id_rubro
WHERE c.id = 1
OR a.id = 1
GROUP BY a.id
a.id, b.id_anunciante, b.id_rubro, c.id are all indexes.
SELECT a.*,
(
SELECT c.id
FROM b
JOIN с
ON c.id = b.id_rubro
WHERE b.id_anunciante = a.id
-- add the ORDER BY condition to define which row will be selected.
LIMIT 1
)
FROM a
Create the index on b (id_anunciante) for this to work faster.
Update:
You don't need the OUTER JOINs here.
Rewrite your query as this:
SELECT a.*, c.id
FROM a
JOIN b
ON b.id_anunciante = a.id
JOIN c
ON c.id = b.id_rubro
WHERE a.id = 1
UNION ALL
SELECT a.*, 1
FROM a
WHERE EXISTS
(
SELECT NULL
FROM c
JOIN b
ON b.id_rubro = c.id
WHERE c.id = 1
AND b.id_anunciante = a.id
)
Add ORDER BY NULL to avoid the implicit sorting MySQL does when doing a group by.
I suppose you have indexes/PKs on a.id, b.id_anunciante, b.id_rubro and c.id ? I guess you could try adding a composite index on (b.id_anunciante, b.id_rubro) if your mysql version is not able to do an index merge.