Question

Complex-sounding question but I suspect the answer may be a little easier!

My WordPress install uses a MySQL database with a table called wp_postmeta.

This table has four columns, meta_id, post_id, meta_key, meta_value.

I have a number of fishkeeping species profiles stored in the wp_posts table which each have an id that links up with the wp_postmeta‘s post_id column.

Each species profile has an entry in the meta table where the meta_key is genus. Similarly they have an entry where the meta_key is species.

wp_posts

    post_id     post_title
    2           Satanoperca daemon (Three spotted daemon)
    4           Betta splendens (Siamese fighting fish)

wp_postmeta

    meta_id     post_id     meta_key    meta_value
    10          2           genus       Satanoperca
    11          2           species     daemon
    12          4           genus       Betta
    13          4           species     splendens

What I need is the genus and species for each species profile I have in the post table, so that I get a list like:

genus       species
Satanoperca daemon
Betta       splendens
Geophagus   steindachneri

Thanks in advance,

Answer 1

SELECT posts.post_id AS post_id, meta1.meta_value AS genus, meta2.meta_value AS species
  FROM wp_posts posts
    LEFT OUTER JOIN wp_postmeta meta1
      ON posts.post_id = meta1.post_id AND meta1.meta_key = "genus"
    LEFT OUTER JOIN wp_postmeta meta2
      ON posts.post_id = meta2.post_id AND meta2.meta_key = "species"