oracle create table primary key

                                    -- Dropping Using alter
ALTER TABLE table_name
DROP CONSTRAINT constraint_name;

                                    -- Primary key in a table
SELECT * FROM ALL_CONSTRAINTS 		-- or DBA_CONSTRAINTS or UESR_CONSTRAINTS
WHERE TABLE_NAME= 'table_name' AND CONSTRAINT_TYPE = 'P';
-- With columns names:
SELECT c.OWNER, c.TABLE_NAME, c.CONSTRAINT_NAME, c.CONSTRAINT_TYPE, 
	col.COLUMN_NAME
FROM ALL_CONSTRAINTS c
JOIN ALL_CONS_COLUMNS col ON c.TABLE_NAME = col.TABLE_NAME 
    AND c.CONSTRAINT_NAME = col.CONSTRAINT_NAME
WHERE c.TABLE_NAME= 'table_name' AND c.CONSTRAINT_TYPE = 'P'
ORDER BY c.TABLE_NAME, c.CONSTRAINT_NAME, col.COLUMN_NAME;

                                    CREATE TABLE table_name
(
  column1 datatype null/not null,
  column2 datatype null/not null,
  ...
  CONSTRAINT constraint_name PRIMARY KEY (column1, column2, ... column_n)
);

                                    -- syntax:
SELECT cols.table_name, cols.column_name, cols.position, cons.status, cons.owner
FROM all_constraints cons, all_cons_columns cols
WHERE cols.table_name = '<table-name>' -- Replace <table-name> with your table-name
AND cons.constraint_type = 'P'
AND cons.constraint_name = cols.constraint_name
AND cons.owner = cols.owner


-- example:
SELECT cols.table_name, cols.column_name, cols.position, cons.status, cons.owner
FROM all_constraints cons, all_cons_columns cols
WHERE cols.table_name = 'CUSTOMERS' 
AND cons.constraint_type = 'P'
AND cons.constraint_name = cols.constraint_name
AND cons.owner = cols.owner