MySQL: Using JOIN statement in a subqery [duplicate] - mysql

Question

This question already has answers here:
Referencing a query result alias in a subquery
(3 answers)
Closed 2 years ago.
Joins can be formulated in an explicit syntax ([INNER|LEFT|OUTER|..] JOIN... ON...) or specifying the conditions in the WHERE statement.
How can I refer to a table called in the external FROM statement and JOIN it in the subquery?
In this case I'm referring to the table with the alias p
SELECT
p.id,
p.post_title,
(SELECT
GROUP_CONCAT(DISTINCT wp_terms.name
SEPARATOR ',')
FROM
p
JOIN
wp_term_relationships ON (p.id = wp_term_relationships.object_id)
LEFT JOIN
wp_term_taxonomy ON (wp_term_relationships.term_taxonomy_id = wp_term_taxonomy.term_taxonomy_id)
LEFT JOIN
wp_terms ON (wp_terms.term_id = wp_term_taxonomy.term_id)
AND wp_term_taxonomy.taxonomy IN ('post_tag' , 'category'))
FROM
`post_senza_revisioni` p
WHERE
p.post_type = 'post'
AND p.post_status = 'publish'
AND p.post_parent = 0
GROUP BY id , post_title

Answer 1

I'm pretty sure you want a correlated subquery:
SELECT p.id, p.post_title,
(SELECT GROUP_CONCAT(DISTINCT wp_terms.nameSEPARATOR ',')
FROM wp_term_relationships tr
wp_term_taxonomy tt
ON tr.term_taxonomy_id = tt.term_taxonomy_id LEFT JOIN
wp_terms t
ON t.term_id = tt.term_id AND
tt.taxonomy IN ('post_tag' , 'category'))
WHERE p.id = r.object_id
)
FROM `post_senza_revisioni` p
WHERE p.post_type = 'post' AND
p.post_status = 'publish' AND
p.post_parent = 0;
I doubt the GROUP BY is needed in the outer query, so I removed it. If you do have duplicate id values in the p table, then you can add it back in -- although that suggests that id is a really bad name for the column.

Answer 2

Without knowing the data you, I think you should be able to use the sub query in the FROM clause, join on the ID and then just select * or your desired columns from the sub query.
SELECT
p.id,
p.post_title,
sub.*
FROM
`post_senza_revisioni` p
JOIN (SELECT
GROUP_CONCAT(DISTINCT wp_terms.name
SEPARATOR ',')
FROM
p
JOIN
wp_term_relationships ON (p.id = wp_term_relationships.object_id)
LEFT JOIN
wp_term_taxonomy ON (wp_term_relationships.term_taxonomy_id = wp_term_taxonomy.term_taxonomy_id)
LEFT JOIN
wp_terms ON (wp_terms.term_id = wp_term_taxonomy.term_id)
AND wp_term_taxonomy.taxonomy IN ('post_tag' , 'category')
) sub
ON p.id = sub.id
WHERE
p.post_type = 'post'
AND p.post_status = 'publish'
AND p.post_parent = 0
GROUP BY id , post_title