Remove unnamed column constraint from a table in Oracle (Helpful link: https://stackoverflow.com/questions/5903632/can-a-subquery-be-used-in-an-oracle-alter-statement)

remove_unnamed_column_constraint_from_table.sql

DECLARE
stmt VARCHAR2(2000);
constr_name VARCHAR2(30);
BEGIN
  SELECT CONSTRAINT_NAME INTO constr_name
   FROM USER_CONS_COLUMNS
   WHERE table_name  = 'YOUR_TABLE' AND
   column_name = 'YOUR_CONSTRAINED_COLUMN';
   stmt := 'ALTER TABLE YOUR_TABLE DROP CONSTRAINT '|| constr_name;
   EXECUTE IMMEDIATE(stmt);
END;