MySQL选择一个复杂的子查询作为字段

Question

I currently have:

SELECT tbl_review.*, users.first_name, users.last_name, (
    SELECT order_ns.tran_date 
    FROM order_ns 
    LEFT JOIN product_2_order_ns.external_order_id = order_ns.order_id 
    WHERE product_2_order_ns.bkfno IN :id
    ORDER BY order_ns.trandate ASC 
    LIMIT 1
) as purchase_date
FROM tbl_review
LEFT JOIN users ON users.sequal_user_id = tbl_review.user_id
WHERE tbl_review.product_id IN :id AND tbl_review.approved = 1

Which, in its sub query, selects an order the user has which has a product in question (defined in :id ) get the the oldest transaction date on file for one of the found orders.

I would really like to keep this to one call of the database (don't really want to call again for each returned user for just one field, or even do a range query of all users) but obviously this particular query isn't working.

What can I do, if anything, to get this working?

I cannot make the sub query into a join since they are two distinct pieces of data, the sub query needs to return detail for each row in the main query.

Answer 1

I think you just want a correlated subquery. It is unclear exactly what the relationship is between the inner query and the outer one. My guess is that it is on users and orders:

SELECT tbl_review.*, users.first_name, users.last_name,
       (SELECT order_ns.tran_date 
        FROM order_ns LEFT JOIN
             product_2_order_ns
             on product_2_order_ns.external_order_id = order_ns.order_id and
                product_2_order_ns.bkfno = tbl_review.product_id and
        WHERE order_ns.user_id = tbl_review.user_id
        ORDER BY order_ns.trandate ASC 
        LIMIT 1
       ) as purchase_date
FROM tbl_review LEFT JOIN
     users
     ON users.sequal_user_id = tbl_review.user_id
WHERE tbl_review.product_id IN :id AND tbl_review.approved = 1;

EDIT:

Oh, the inner query has no relationship to the outer query. Then it is easier. Move it to the from clause using cross join :

SELECT tbl_review.*, users.first_name, users.last_name,
       innerquery.tran_date as purchase_date
FROM tbl_review LEFT JOIN
     users
     ON users.sequal_user_id = tbl_review.user_id cross join
     (SELECT order_ns.tran_date 
      FROM order_ns LEFT JOIN
           product_2_order_ns
           on product_2_order_ns.external_order_id = order_ns.order_id 
      WHERE product_2_order_ns.bkfno IN :id
      ORDER BY order_ns.trandate ASC 
      LIMIT 1
     ) innerquery
WHERE tbl_review.product_id IN :id AND tbl_review.approved = 1;

Answer 2

@Gordons answer is really close but I wanted it to return even if no data was found for tran_date so I changed my query to:

SELECT tbl_review.*, users.first_name, users.last_name, order_ns.tran_date
FROM tbl_review
LEFT JOIN users ON users.sequal_user_id = tbl_review.user_id 
LEFT JOIN order_ns ON order_ns.order_id = (
    SELECT order_ns.order_id 
    FROM order_ns
    LEFT JOIN product_2_order_ns on product_2_order_ns.external_order_id = order_ns.order_id
            WHERE product_2_order_ns.bkfno IN :id
    ORDER BY order_ns.tran_date ASC
    LIMIT 1
 ) 
 WHERE tbl_review.product_id IN :id AND tbl_review.approved = 1;    

This will return the distinct data of tran_date irrespective of whether it is found or not.