How to view contraints of a cloumn in postgresSql? I applied a constraint but forgot its name. Now I want to drop it using ALTER TABLE [TABLENAME] DROP CONSTRAINT [CONSTRAINTNAME] . If there is a way to drop all constraint from a column that should work too. 
I cannot use psql command.
PostgreSQL exposes the constraints as well as other schema details through information_schema, so to find all the constraints for the table, query table_constraints, for example:

SELECT constraint_name FROM information_schema.table_constraints
    WHERE table_name='my_table' AND constraint_type='UNIQUE';


To find which columns are involved into the constraints, check constraint_column_usage.