SQL left join vs multiple tables on FROM line?

Question

Most SQL dialects accept both the following queries:

SELECT a.foo, b.foo
FROM a, b
WHERE a.x = b.x

SELECT a.foo, b.foo
FROM a
LEFT JOIN b ON a.x = b.x
         


        

Answer 1

The SELECT * FROM table1, table2, ... syntax is ok for a couple of tables, but it becomes exponentially (not necessarily a mathematically accurate statement) harder and harder to read as the number of tables increases.

The JOIN syntax is harder to write (at the beginning), but it makes it explicit what criteria affects which tables. This makes it much harder to make a mistake.

Also, if all the joins are INNER, then both versions are equivalent. However, the moment you have an OUTER join anywhere in the statement, things get much more complicated and it's virtually guarantee that what you write won't be querying what you think you wrote.