Relax the definition of unique on columns (psql)

- Fix formatting on giant postgres query
- Invert the section that looks for unique constraints to look for a
  constraint and join to the constraint_column_usage to be more in line
  with the mysql query and also it makes a little bit more sense.
- Add more checks to ensure the schema is being enforced in the postgres
  side of things as several pieces in the unique checks were missing it
  which would lead to false positives.
- Fix #77 for postgres

bdb/drivers/postgres.go

@@ -155,16 +155,17 @@ func (p *PostgresDriver) Columns(schema, tableName string) ([]bdb.Column, error)
 		c.is_nullable = 'YES' as is_nullable,
 		(select exists(
 			select 1
-				from information_schema.constraint_column_usage as ccu
-			inner join information_schema.table_constraints tc on ccu.constraint_name = tc.constraint_name
-			where ccu.table_name = c.table_name and ccu.column_name = c.column_name and tc.constraint_type = 'UNIQUE'
-			)) OR (select exists(
+			from information_schema.table_constraints tc
+			inner join information_schema.constraint_column_usage as ccu on tc.constraint_name = ccu.constraint_name
+			where tc.table_schema = $1 and tc.constraint_type = 'UNIQUE' and ccu.constraint_schema = $1 and ccu.table_name = c.table_name and ccu.column_name = c.column_name and
+				(select count(*) from information_schema.constraint_column_usage where constraint_schema = $1 and constraint_name = tc.constraint_name) = 1
+		)) OR
+		(select exists(
 			select 1
-			from
-				pg_indexes pgix
-				inner join pg_class pgc on pgix.indexname = pgc.relname and pgc.relkind = 'i'
-				inner join pg_index pgi on pgi.indexrelid = pgc.oid
-				inner join pg_attribute pga on pga.attrelid = pgi.indrelid and pga.attnum = ANY(pgi.indkey)
+			from pg_indexes pgix
+			inner join pg_class pgc on pgix.indexname = pgc.relname and pgc.relkind = 'i' and pgc.relnatts = 1
+			inner join pg_index pgi on pgi.indexrelid = pgc.oid
+			inner join pg_attribute pga on pga.attrelid = pgi.indrelid and pga.attnum = ANY(pgi.indkey)
 			where
 				pgix.schemaname = $1 and pgix.tablename = c.table_name and pga.attname = c.column_name and pgi.indisunique = true
 		)) as is_unique
@@ -173,7 +174,7 @@ func (p *PostgresDriver) Columns(schema, tableName string) ([]bdb.Column, error)
 		left join information_schema.element_types e
 			on ((c.table_catalog, c.table_schema, c.table_name, 'TABLE', c.dtd_identifier)
 			= (e.object_catalog, e.object_schema, e.object_name, e.object_type, e.collection_type_identifier))
-		where c.table_name=$2 and c.table_schema = $1;
+		where c.table_name = $2 and c.table_schema = $1;
 	`, schema, tableName)
 
 	if err != nil {