Перезаписать данные в таблице A, если данные присутствуют в таблице B, + отобразить на собственные перезаписанные данные, если присутствует внешний ключ для другого идентификатора

Question

У нас есть 2 таблицы, которые предоставляют список школ.

Первая таблица (school_data) - это исходные данные из общедоступной базы данных, которая обновляется при публикации правительством новых данных.

Вторая таблица school_data_overwrites имеет большинство тех же полей и используется для исправления опечаток и неточностей в первой таблице (она находится в отдельной таблице, чтобы иметь возможность обновлять данные, сохраняя наши правки).

Затем мы используем представление, которое должен запрашивать наш код, который для каждой строки должен показывать значение от school_data_overwrites, если оно присутствует, или откат до school_data, если его нет. Что является сложным, так это то, что некоторые строки имеют parent_school_id, который ссылается на другую строку, которая сама может иметь перезаписанные данные.

Мы получили следующее представление, но оно очень медленное и использует много ресурсов ЦП:

SELECT
    school_data.id AS id,
    school_data.ref_id AS ref_id,
    school_data.schoolyear AS schoolyear,

    IF(school_data_overwrites.type <> '' OR school_data_overwrites.type <> NULL, school_data_overwrites.type, school_data.type) AS type,
    IF(school_data_overwrites.name <> '' OR school_data_overwrites.name <> NULL, school_data_overwrites.name, school_data.name) AS name,
    IF(school_data_overwrites.email <> '' OR school_data_overwrites.email <> NULL, school_data_overwrites.email, school_data.email) AS email,
    IF(school_data_overwrites.certified_email <> '' OR school_data_overwrites.certified_email <> NULL,  school_data_overwrites.certified_email, school_data.certified_email) AS certified_email,
    IF(school_data_overwrites.website <> '' OR school_data_overwrites.website <> NULL, school_data_overwrites.website,  school_data.website) AS website,
    IF(school_data_overwrites.address <> '' OR school_data_overwrites.address <> NULL, school_data_overwrites.address, school_data.address) AS address,
    IF(school_data_overwrites.postcode <> '' OR school_data_overwrites.postcode <> NULL,  school_data_overwrites.postcode, school_data.postcode) AS postcode,

    school_data.city_id AS city_id,
    school_data.city_name AS city_name,
    school_data.province_id AS province_id,
    school_data.province_name AS province_name,
    school_data.province_iso_code AS province_iso_code,
    school_data.region_id AS region_id,
    school_data.region_name AS region_name,
    school_data.nuts3_2010_code AS nuts3_2010_code,

    school_data_overwrites.facebook_url AS facebook_url,
    school_data_overwrites.twitter_url AS twitter_url,
    school_data_overwrites.vip AS vip,

    school_data.parent_school_id AS parent_school_id,
    IF(school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL, parent_school_data.city_id, '') parent_school_ref_id,
    IF(school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL, parent_school_data.city_id, '') parent_school_schoolyear,

    IF(
        school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL,
        IF(parent_school_data_overwrites.type <> '' OR parent_school_data_overwrites.type <> NULL, parent_school_data_overwrites.type, parent_school_data.type),
                ''
    ) AS parent_school_type,
    IF(
        school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL,
        IF(parent_school_data_overwrites.name <> '' OR parent_school_data_overwrites.name <> NULL, parent_school_data_overwrites.name, parent_school_data.name),
                ''
    ) AS parent_school_name,
    IF(
        school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL,
        IF(parent_school_data_overwrites.email <> '' OR parent_school_data_overwrites.email <> NULL, parent_school_data_overwrites.email, parent_school_data.email),
                ''
    ) AS parent_school_email,
    IF(
        school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL,
        IF(parent_school_data_overwrites.certified_email <> '' OR parent_school_data_overwrites.certified_email <> NULL, parent_school_data_overwrites.certified_email, parent_school_data.certified_email),
                ''
    ) AS parent_school_certified_email,
    IF(
        school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL,
        IF(parent_school_data_overwrites.website <> '' OR parent_school_data_overwrites.website <> NULL, parent_school_data_overwrites.website, parent_school_data.website),
                ''
    ) AS parent_school_website,
    IF(
        school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL,
        IF(parent_school_data_overwrites.address <> '' OR parent_school_data_overwrites.address <> NULL, parent_school_data_overwrites.address, parent_school_data.address),
                ''
    ) AS parent_school_address,
    IF(
        school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL,
        IF(parent_school_data_overwrites.postcode <> '' OR parent_school_data_overwrites.postcode <> NULL, parent_school_data_overwrites.postcode, parent_school_data.postcode),
                ''
    ) AS parent_school_postcode,

    IF(school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL, parent_school_data.city_id, '') AS parent_school_city_id,
    IF(school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL, parent_school_data.city_name, '') AS parent_school_city_name,
    IF(school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL, parent_school_data.province_id, '') AS parent_school_province_id,
    IF(school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL, parent_school_data.province_name, '') AS parent_school_province_name,
    IF(school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL, parent_school_data.province_iso_code, '') AS parent_school_province_iso_code,
    IF(school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL, parent_school_data.region_id, '') AS parent_school_region_id,
    IF(school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL, parent_school_data.region_name, '') AS parent_school_region_name,
    IF(school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL, parent_school_data.nuts3_2010_code, '') AS parent_school_nuts3_2010_code,

    IF(school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL, parent_school_data_overwrites.facebook_url, '') AS parent_school_facebook_url,
    IF(school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL, parent_school_data_overwrites.twitter_url, '') AS parent_school_twitter_url,
    IF(school_data.parent_school_id <> '' OR school_data.parent_school_id <> NULL, parent_school_data_overwrites.vip, '') AS parent_school_vip
FROM
    school_data LEFT JOIN school_data_overwrites ON school_data_overwrites.school_id = school_data.id,
    school_data parent_school_data LEFT JOIN school_data_overwrites parent_school_data_overwrites ON parent_school_data_overwrites.school_id = parent_school_data.parent_school_id
WHERE parent_school_data.id = school_data.id;

school_data выглядит так:

+---------------------------------+--------------+------+-----+---------+-------+
| Field                           | Type         | Null | Key | Default | Extra |
+---------------------------------+--------------+------+-----+---------+-------+
| id                              | varchar(255) | YES  |     | NULL    |       |
| ref_id                          | varchar(255) | YES  |     | NULL    |       |
| schoolyear                      | int(11)      | YES  | MUL | NULL    |       |
| type                            | varchar(255) | YES  | MUL | NULL    |       |
| name                            | varchar(255) | YES  | MUL | NULL    |       |
| email                           | varchar(255) | YES  | MUL | NULL    |       |
| certified_email                 | varchar(255) | YES  | MUL | NULL    |       |
| website                         | varchar(255) | YES  |     | NULL    |       |
| address                         | varchar(255) | YES  | MUL | NULL    |       |
| cad_code                        | varchar(255) | YES  | MUL | NULL    |       |
| postcode                        | varchar(255) | YES  | MUL | NULL    |       |
| city_name                       | varchar(255) | YES  | MUL | NULL    |       |
| city_id                         | varchar(255) | YES  | MUL | NULL    |       |
| province_name                   | varchar(255) | YES  | MUL | NULL    |       |
| province_id                     | varchar(255) | YES  | MUL | NULL    |       |
| province_iso_code               | varchar(255) | YES  | MUL | NULL    |       |
| region_name                     | varchar(255) | YES  | MUL | NULL    |       |
| region_id                       | varchar(255) | YES  | MUL | NULL    |       |
| nuts3_2010_code                 | varchar(255) | YES  | MUL | NULL    |       |
| parent_school_id                | varchar(255) | YES  | MUL | NULL    |       |

Это school_data_overwrites:

+---------------------------+------------------+------+-----+---------+----------------+
| Field                     | Type             | Null | Key | Default | Extra          |
+---------------------------+------------------+------+-----+---------+----------------+
| id                        | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| school_id                 | varchar(255)     | NO   | UNI | NULL    |                |
| type                      | varchar(255)     | YES  | MUL | NULL    |                |
| name                      | varchar(255)     | YES  | MUL | NULL    |                |
| email                     | varchar(255)     | YES  | MUL | NULL    |                |
| certified_email           | varchar(255)     | YES  | MUL | NULL    |                |
| website                   | varchar(255)     | YES  | MUL | NULL    |                |
| address                   | varchar(255)     | YES  | MUL | NULL    |                |
| postcode                  | varchar(255)     | YES  | MUL | NULL    |                |
| city_id                   | varchar(255)     | YES  |     | NULL    |                |
| facebook_url              | varchar(255)     | YES  |     | NULL    |                |
| twitter_url               | varchar(255)     | YES  |     | NULL    |                |
| email_they_read           | tinyint(4)       | YES  |     | 0       |                |
| certified_email_they_read | tinyint(4)       | YES  |     | 0       |                |
| vip                       | tinyint(4)       | YES  |     | 0       |                |
| created_at                | timestamp        | YES  |     | NULL    |                |
| updated_at                | timestamp        | YES  |     | NULL    |                |
+---------------------------+------------------+------+-----+---------+----------------+

Мы не знаем, как его оптимизировать. Я думаю, что мы включили слишком много условий, и есть более простой способ.

Как мы можем сделать это представление более производительным?