PostGIS - st_intersects: WHERE vs INNER JOIN

Question

In PostgreSQL/PostGIS, when running an intersection between 2 geometries, what the difference between these two syntaxes ?

-- Method 1
SELECT
a.id
b.id
FROM a, b
WHERE st_intersects(a.geom, b.geom)

-- Method 2
SELECT
a.id,
b.id
FROM a
INNER JOIN b ON st_intersects(a.geom, b.geom)

In real conditions, first method is longer to execute than second for the same result. Instinctively I would have believed the opposite because the first had one condition, how to explain this ?

An EXPLAIN ANALYZE SELECT with the unrolled detail did not enlighten me more (here is an example with real tables, the names do not match the example above).

Method 1

Method 2

I'm using PostgreSQL 13.2 and PostGIS 3.1.1.

Answer 1

a INNER JOIN b ON is the same as a JOIN b ON, which is the same as SELECT FROM a,b WHERE. Your 2 queries are functionally identical.

...FROM a,b WHERE st_intersects(a.geom,b.geom)

is the same as

...FROM a INNER JOIN b ON st_intersects(a.geom,b.geom)

is the same as

...FROM a JOIN b ON st_intersects(a.geom,b.geom)