由于使用子查询将查询重写为使用联接的查询而导致的SQL错误

Question

The original query:

SELECT      o.offering_number,
        o.english_description,
        o.french_description,
        fop.price_amount,
        fop.price_type_code,
        fop.price_status_code,
        fop.offering_id,
        (SELECT fop1.price_amount from facility_offering_price fop1
                WHERE fop.offering_id = fop1.Offering_Id
                    AND fop1.price_type_code = 5
                AND fop1.price_status_code = 3
            ) as 'priceAmount'
            from facility_offering_price fop
            join offering o on fop.offering_id = o.offering_id
                WHERE fop.price_start_date = '15-10-28'
                AND fop.price_status_code IN (1,2)
                /*AND (price_status_code IS NULL)*/
                AND fop.price_type_code = 5
                /*AND (o.offering_number IS NULL)*/
                    ORDER BY o.offering_number ASC, fop.price_sequence_number ASC;

It produces a result of one entry.

The result query:

SELECT      o.offering_number,
        o.english_description,
        o.french_description,
        fop.price_amount,
        fop2.price_amount,
        fop.price_type_code,
        fop.offering_id,
        fop2.offering_id
            from facility_offering_price fop
            join offering o on fop.offering_id = o.offering_id
            inner join
                (select
                    fop1.offering_id,
                    fop1.price_amount
                            from facility_offering_price fop1
                            WHERE fop1.price_type_code = 5
                            AND fop1.price_status_code = 3
                ) fop2 on fop.offering_id = fop2.offering_id
                WHERE fop.price_start_date = '15-10-28'
                AND fop.price_status_code IN (1,2)
                /*AND (price_status_code IS NULL)*/
                AND fop.price_type_code = 5
                /*AND (o.offering_number IS NULL)*/
                    ORDER BY o.offering_number ASC, fop.price_sequence_number ASC;

It's result set is empty. However, an entry is found if I ask for fop1.price_status_code = 1.

Unable to wrap my head around this one I would appreciate your help.

Answer 1

Try using LEFT JOIN instead. The conversion from SELECT a, subquery AS val FROM ... to a join is more accurately reflected that way. The original query would return rows with NULL val when the subquery has no results; your version ends up omitting such rows completely.