php - SQL Query based on value of a different row -


i'm trying query data multiple tables cannot seem achieve type of join. example, have 1 table contains products, , wp_usermeta table various user meta data:

products table

serial #     product --------------------- 0001         0002         b 0003         c

wp_usermeta (simplified)

user id     key         value -------------------------------- 1           serials     0001 1           company     company 2           serials     0001 2           company     company b 3           serials     0001 3           company     company c

i need company name based on serial numbers own, such as:

serial #      company ------------------------- 0001          company 0002          company b 0003          company c

i've been able retrieve user id based on serial number simple join query, dont know go there.

select products.serial_number, wp_usermeta.user_id products left join wp_usermeta on products.serial_number = wp_usermeta.meta_value

i not sure products table has results need.

one method "simple" self-join:

select p.value serial_number, c.value company.user_id wp_usermeta p join      wp_usermeta c      on p.user = c.user ,         p.key = 'serials' ,         c.key = 'company';

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