Rough notes on status, probably a bit out of date. You can also see the test files:

http://bazaar.launchpad.net/~jakewheat/hssqlppp/trunk/annotate/head%3A/Database/HsSqlPpp/Tests/ParserTests.lhs

and

http://bazaar.launchpad.net/~jakewheat/hssqlppp/trunk/annotate/head%3A/Database/HsSqlPpp/Tests/AstCheckTests.lhs

to see a load of examples of what type checks.

= Syntax supported/ not supported:

== Parsing

Partially supports:
select statements (selectlists (*, qualified, aliased/correlation names, expressions)
       distinct, basic window functions,
       from (with explicit joins - natural, inner, cross, left, right,
       full outer, on and using), aliases, from functions
       where, group by, having, order by, limit, offset
       except, intersect, union

expressions: subselects, in, row ctors, strings + dollar strings,
             integers, case, exists, boolean literals, null, arrays
             and subscripting (slightly limited), function calls,
             identifiers, cast(x as y), between (quite limited),
             substring(x from a for b)

also partially supports:
insert (with multiple values and select support), update, delete (all
three with returning)
create and drop table, type, view, domain
create function for sql and plpgsql functions
all constraint types
sort of skips copy statements instead of erroring

plpgsql statements:
        select into
        null
        continue
        perform
        execute
        assignment
        if
        return, return next, return query
        raise
        for (select and integer variants)
        while
        case statement

Many things are missing at the moment, in particular
  selects: cte, implicit joins
  joins in updates (delete from, update using)
  alter statements
  create and drop apart from table, view, domain, type, function
  transaction commands
  triggers and trigger functions
  loop statement, labels
  error trapping
  cursors
This is a non-exhaustive list.

Expression support is patchy, should work pretty well for a lot of
simple stuff though. There is a strong possibility that for some
complex selects and expressions, the implicit precedence (that is,
bits without enclosing parenthesis) may parse in the wrong
direction. Please let me know if you encounter such an error.

== Type checking

Type checking supports a good subset of expressions and select
statements that the parser parses, and has basic support for insert,
update, delete and the various create statements that the parser
supports. Development work is currently focused in this area.

= Other current downsides:

The design of the AST node types is pretty basic.

Not much work has been done on correctly rejecting invalid SQL
(although it does pretty well despite this) and not much thought has
been put into error messages and error reporting yet, this is slowly
improving, and at some point will become a major focus - I hope this
code will provide substantial benefits when developing in PL/pgSQL in
the future.

Only supports PostgreSQL SQL and PL/pgSQL.