Question

I have below SQL command that works to get user_meta details in WordPress. This works fine to get the data in one table and one row per user info with info for each user in each column but I’m just trying to find out how this works. Can anyone be kind enough to explain below?:

SELECT
    u.id, u.user_login,
    MIN(CASE m.meta_key WHEN 'title' THEN m.meta_value END) AS title,
    MIN(CASE m.meta_key WHEN 'first_name' THEN m.meta_value END) AS first_name,
    MIN(CASE m.meta_key WHEN 'last_name' THEN m.meta_value END) AS last_name,
    MIN(CASE m.meta_key WHEN 'suburb' THEN m.meta_value END) AS phone,
    MIN(CASE m.meta_key WHEN 'state' THEN m.meta_value END) AS state,
    MIN(CASE m.meta_key WHEN 'country' THEN m.meta_value END) AS country,
    MIN(CASE m.meta_key WHEN 'postcode' THEN m.meta_value END) AS postcode,
    MIN(CASE m.meta_key WHEN 'contact_no' THEN m.meta_value END) AS contact_no,
    MIN(CASE m.meta_key WHEN 'email' THEN m.meta_value END) AS email,
    MIN(CASE m.meta_key WHEN 'occupation' THEN m.meta_value END) AS occupation,
    MIN(CASE m.meta_key WHEN 'workplace' THEN m.meta_value END) AS workplace,
    MIN(CASE m.meta_key WHEN 'maternitybg' THEN m.meta_value END) AS maternitybg,
    MIN(CASE m.meta_key WHEN 'trainingdate' THEN m.meta_value END) AS trainingdate,
    MIN(CASE m.meta_key WHEN 'traininglocation' THEN m.meta_value END) AS traininglocation,
    MIN(CASE m.meta_key WHEN 'coltraining' THEN m.meta_value END) AS coltraining,
    MIN(CASE m.meta_key WHEN 'trainingyear' THEN m.meta_value END) AS trainingyear,
    MIN(CASE m.meta_key WHEN 'coltraining' THEN m.meta_value END) AS coltraining,
    MIN(CASE m.meta_key WHEN 'isinstructor' THEN m.meta_value END) AS isinstructor,
    MIN(CASE m.meta_key WHEN 'gender' THEN m.meta_value END) AS gender,
    MIN(CASE m.meta_key WHEN 'idf_indig_tsi' THEN m.meta_value END) AS idf_indig_tsi,
    MIN(CASE m.meta_key WHEN 'idf_ct_ld' THEN m.meta_value END) AS idf_ct_ld,
    MIN(CASE m.meta_key WHEN 'comments' THEN m.meta_value END) AS comments

    FROM wp_users u
      LEFT JOIN wp_usermeta m ON u.ID = m.user_id
        AND m.meta_key IN ('title', 'first_name', 'last_name', 'suburb', 'state', 'country', 'postcode', 'contact_no', 'email', 'occupation', 'workplace', 'maternitybg', 'trainingdate', 'traininglocation', 'coltraining', 'isinstructor', 'gender', 'idf_indig_tsi', 'idf_ct_ld', 'comments')
    GROUP BY u.ID

Thanks for your help!

Answer 1

Not sure what part you want explained but anyway, here we go

This part is about specifying what columns you want:

SELECT
    u.id, u.user_login,

Followed by the part where you include the source tables:

FROM wp_users u
  LEFT JOIN wp_usermeta m ON u.ID = m.user_id

By using left join you make sure that you will get rows from wp_users even if there are no matches in wp_usermeta. ON u.ID = m.user_id connect the rows between wp_users and wp_usermeta.

Apparently, wp_usermeta is key-value table and this limits the keys you are interested in.

AND m.meta_key IN ('title', 'first_name', 'last_name', 'suburb', 'state', 'country', 'postcode', 'contact_no', 'email', 'occupation', 'workplace', 'maternitybg', 'trainingdate', 'traininglocation', 'coltraining', 'isinstructor', 'gender', 'idf_indig_tsi', 'idf_ct_ld', 'comments')

Finally there is group by clause that will make the output one row for each distinct value of u.ID.

GROUP BY u.ID

There is a little trick in the field list as well using a case statement.

MIN(CASE m.meta_key WHEN 'title' THEN m.meta_value END) AS title,

First you get the value m.meta_value if the m.meta_key equals 'title', otherwise the value will by null.

CASE m.meta_key WHEN 'title' THEN m.meta_value END

If there are more than one 'title' keys in wp_usermeta for a given user you will get the min() value. Title ‘Bus driver’ will be picked before title ‘Cab driver’.

MIN(CASE m.meta_key WHEN 'title' THEN m.meta_value END)

And at last you give the column retrieved a column alias title.

MIN(CASE m.meta_key WHEN 'title' THEN m.meta_value END) AS title,