What is the difference between two types of multi-table queries in MySQL?

Question

SQL 1:

SELECT
    a.*,
    b.name
FROM
    t_coach a
LEFT JOIN t_school b on a.school_id=b.id

SQL 2:

SELECT a.*, (select b.name FROM t_school b WHERE b.id= a.school_id) AS name  FROM t_coach a

SQL1 and SQL2 get the same result.

Can the second SQL be written like this in actual development?
Compared with SQL1, is SQL2 less efficient?

Answer 1

SQL1, table B is only scanned once
SQL2, table B will be scanned as many times as there are records in table A
When the amount of data in your database is enough, SQL2 will not be able to produce results directly, and will kill the database