Limit a Left Join on the first table - mysql

Question

I have two tables: gems and gemdetail that are left joined. I am trying to limit the LEFT JOIN to 10 records in the gems table. There are 2 other tables joined (gemreply and users) as well, but they do not contribute to the problem. The following does not work:
SELECT
gems.gemid,
gems.title,
r.tot,
gemdetail.filename
FROM
(
(
gems
LEFT JOIN(
SELECT
gemid,
COUNT(*) AS tot
FROM
gemreply
GROUP BY
gemid
) AS r
ON
gems.gemid = r.gemid
)
LEFT JOIN gemdetail ON gems.gemid = gemdetail.gemid
)
LEFT JOIN users ON gems.userid = users.userid
WHERE
gems.grade = '7'
ORDER BY
gems.gemid
LIMIT 0, 10;
This limits the total number of returned rows to 10, but since there are multiple detail records for each gem, I am left with fewer than 10 gem records. I've read every "LIMIT" post, but haven't found this situation.
This version of MySQL doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery'.

Answer 1

Something like that
SELECT * FROM A
INNER JOIN ( SELECT * FROM A WHERE A.FIELD1='X' ORDER BY A.FIELD2 LIMIT 10) X
ON (A.KEYFIELD=X.KEYFIELD)
LEFT JOIN B ON (A.FIELD = B.FIELD)
LEFT JOIN C ON (A.FIELD = C.FIELD)

Answer 2

Try this:
SELECT g.gemid, g.title, r.tot, gemdetail.filename
FROM (SELECT * FROM gems WHERE grade = '7' LIMIT 10) g
LEFT JOIN (SELECT gemid, COUNT(*) AS tot FROM gemreply GROUP BY gemid) r
ON r.gemid = g.gemid
LEFT JOIN gemdetail ON g.gemid = gemdetail.gemid
LEFT JOIN users ON g.userid = users.userid
ORDER BY g.gemid;
This should work.

Answer 3

Ten years later, I can LIMIT records within a nested query on the left table of a one to many JOIN where more than one record will be returned for the left table--even when there is a WHERE or ORDER BY clause on fields on the right side tables of the join.
In the inner query, have all the tables with joins necessary to satisfy the WHERE clause. Apply the limit there.
In the outer query, rejoin to all the same tables to add the many to many fields
SELECT
alias.field_from_A,
alias.field_from_B
FROM (
SELECT DISTINCT
/* ONLY fields from LEFT table (or tables
with a one to one relationship with it) will
allow LIMIT to apply only to the LEFT table. DISTINCT is needed due to JOIN*/
A.field_from_A
FROM
A
/* JOIN to your hearts content on tables
which need to satisfy WHERE and ORDER BY */
LEFT JOIN B ON A.field_from_A = B.field_from_B
WHERE A.field_from_A = 'value' AND B.field_from_B = 'value 2'
ORDER BY A.field_from_A, B.field_from_B
LIMIT 0, 10
) alias
/* JOIN the one to many tables here to add the field info */
LEFT JOIN B ON A.field_from_A = B.field_from_B
/* the WHERE and ORDER BY need to be applied again */
WHERE alias.field_from_A = 'value' AND B.field_from_B = 'value 2'
ORDER BY alias.field_from_A, B.field_from_B

Answer 4

WITH last_orders AS (
SELECT *
FROM orders
WHERE id IN (
SELECT MAX(id)
FROM orders
GROUP BY customer_id
)
)
SELECT customers.id, customers.first_name, customers.last_name,
last_orders.order_date, last_orders.order_status
FROM customers
JOIN last_orders
ON customers.id = last_orders.customer_id
ORDER BY customer_id;