Am I using JOIN correctly in mysql?

Question

MySQL

Right now I'm using something like this

SELECT * 
FROM `city` 
LEFT JOIN `raion` ON `raion`.`id` = `city`.`raion`
LIMIT 5

There are a large number of records in the city and raion tables, and in the original there are several joins and I wondered about optimization. There is a LIMIT in the request and I wondered at what stage it works, before the join or after.
If he first searches for many records for many cities and then takes only 5 results, then this creates a load, and if he takes five cities and then looks at the districts through them, then this is normal. What can you explain?
Maybe it was easier to loop through city and make five quick requests to raion?
I decided to add a combat example. Do not judge strictly. right now I decided to do the optimization)

EXPLAIN SELECT z.*, fq.`text` AS `question`,  c.id AS `clientYes`, u.`name` AS nameUslug, city.`name` AS cityName, COUNT(zl.`id`) AS `count_zl`, p.`name` AS `partner_name`
FROM `zaiavki` z 
LEFT JOIN `ankets` a ON a.`id` = z.`anketa`
LEFT JOIN `clients` c ON c.phone = z.phone
LEFT JOIN `uslugi` u ON z.usluga = u.id
LEFT JOIN `city` ON city.id = z.city
LEFT JOIN `faq_question` fq ON fq.`zaiavka` = z.`id`
LEFT JOIN `zaiavki_nocall_log` zl ON zl.`id` = z.`id`
LEFT JOIN `partners` p ON p.`id` = z.`partner`
WHERE  z.`status` = '0'  AND  z.`delete` = '1'     
GROUP BY z.id ORDER BY z.dateCreated DESC, z.id DESC LIMIT 0, 20

Answer 1

Vyacheslav Belyaev : look at Type = all this means a full pass through the table try to add an index so as not to select all records from join tables

Answer 2

EXPLAIN will answer all your questions . The mysql optimizer can generate a different execution plan for the same query depending on the size of the tables, how they are used, and a bunch of other factors, so it's impossible to answer your question unambiguously - you need to look at specific data.
https://habrahabr.ru/post/211022/