Re: Is it possible to left join based on previous joins result

I tried the example as the following:

create table a(col1);
create table b(col1, col2)

select a.*
from a inner join b using(col2)
left join b.col2 as c on (c.col1 = a.col1)

System notifies me that b is not a schema name.

So, I guess the approach that I tried to do is not acceptable by Pgsql
grammar.

the syntax is
LEFT JOIN [table] AS ...

you have b.col2 which means the database will interpret col2 as the table name and subsequently b as the schema name

You should have
SELECT a.*
FROM a
INNER JOIN b using(col2)
LEFT JOIN b as c on (c.col1 = a.col1)

In the "using(col2)", what columns and tables are you joining there?  I always dislike that syntax as it is ambiguous in some cases and not very easy to read.