Question

I’m having a bit of a problem with a task I was assigned.

I have this old phpmynewsletter database (MySQL backend).

Basically all emails are saved in a table with this structure:

    email   varchar(255)
    list_id int(11)
    hash    varchar(255)
    disclaimer1 tinyint(1)
    disclaimer2 tinyint(1)
    gender  char(1)
    dob date
    region  varchar(50)

So one same email can be present several times in the table, this is, subscribed in different newsletters (identified by list_id)

What I need to do is update the records so the fields disclaimer1, disclaimer2, gender, dob and region for a specific list_id are the same for the same email registered with other list_id’s.

For example:

    email: email1(at)gmail.com
    list_id: 1
    disclaimer1: 0
    disclaimer2: 0
    gender: M
    dob: 1975-05-02
    region: Portugal

and

    email: email2(at)gmail.com
    list_id: 33
    disclaimer1: 1
    disclaimer2: 0
    gender: M
    dob: 1975-05-02
    region: Portugal

How do I update the record with list_id 33 with the correct values from record with list_id 1?

I’m using PHP and I believe that running updates queries in loops is bad practise. The table has around 610000 records.

Hope somebody can give me some insight on how to accomplish this task.

Thanks,
Mário

Answer 1

@bigman what you have posted seems to be right but I guess the question is on how to change all the other data similar to list_id: 1 with the same email.

UPDATE my_table t,
 (
    SELECT
        email,
        disclaimer1,
        disclaimer2,
        gender,
        dob,
        region
    FROM
        my_table
    WHERE
        list_id = 1
) t1
SET 
 t.disclaimer1 = t1.disclaimer1,
 t.gender = t1.gender,
 t.dob = t1.dob,
 t.region = t1.region
WHERE
   t.email = t1.email

I guess this should work for all the entries that would have the list_id: 1 email address.