sql - Why the below join query returns different result? -

1st query - select * full outer join b on a.x = b.y b.y = 10

2nd query - select * full outer join b on a.x = b.y , b.y = 10

consider these table extensions:

 table table b  ======= =======   x       y  -----   -----  1       2  5       5  10      10 

the first query return:

 10 10 

and, second query return:

 1 null  5 null  10 10 

could please let me know reasons in detail ?

the first query gives expected result.

but second query's result different because joining tables on both conditions(a.x = b.y , b.y = 10). , since outer join, it'll print values satisfy , null , output. created sql fiddle can understand better