Question

I have a table called ‘people’ and people has an associated table named ‘appearances’. I’d like to update the people table with the ‘appearance_count’ selected with a left join in MySQL. I’m just having some trouble with the syntax. Where would I put my update statement in the following query. I tried an update similar to this but I kept getting an error ‘cannot update same table as selected table’ (or something to that effect). Here is my query in its raw select form:

 SELECT        people.*, 
 COUNT(appearances.id) as app_count,
 FROM          `people`
 INNER JOIN    `appearances`
 ON            `appearances`.`person_id` = `people`.`id`
 GROUP BY      `people`.`id`
 HAVING        app_count > 0;

How would I take “app_count” and set people.appearance_count to be that value?

Answer 1

I think HAVING is not necessary because it will filter records that have a COUNT of greater than zero and you’re joining it with table PEOPLE using LEFT JOIn.

UPDATE  people a
        LEFT JOIN
        (
            SELECT b.id, COUNT(c.person_ID) totalCOunt
            FROM    people b
                    INNER JOIN    appearances c
                        ON c.person_id = b.id
            GROUP BY b.id
        ) d ON a.ID = d.ID
SET     a.appearance_count = d.totalCount