Question

Is there any efficiency difference in an explicit vs implicit inner join? For example:

SELECT * FROM table a INNER JOIN table b ON a.id = b.id; 

vs.

SELECT a.*, b.* FROM table a, table b WHERE a.id = b.id; 

Answer 1

Performance-wise, they are exactly the same (at least in SQL Server).

PS: Be aware that the "implicit OUTER JOIN" syntax–using *= or =* in a WHERE after using comma–is deprecated since SQL Server 2005. (The "implicit (CROSS) JOIN" syntax using comma as used in the question is still supported.)

Deprecation of "Old Style" JOIN Syntax: Only A Partial Thing