Question

Let A and B be two tables in a database schema. A and B are related by a many-to-one relationship. There exists many B’s for each A, and B has a foreign key column a_id. Both tables have a primary key column id.

Which of the following two queries performs better for large data sets in A and B?

SELECT A.* FROM A,B WHERE A.id = B.a_id

or

SELECT A.* FROM A INNER JOIN B ON A.id = B.a_id

Or are they equivalent?

Answer 1

They are equivalent for all 4 major database systems: Oracle, SQL Server, MySQL, PostgreSQL.

Using JOIN syntax (to be more exact, using STRAIGHT_JOIN instead of JOIN) will help to enforce the join order you need in MySQL.

See this answer for details:

• Does the order of tables matter?

It’s also generally considered more clean and readable to use the JOIN syntax.

Though I’m grown on Oracle code samples which generally use the WHERE syntax.