Oracle query - increase - delete - modify the primary key

The operation of Oracle primary key table, there are four types: query, add, modify, delete

1, the primary key query

/ * Query the constraints that exist in a table * / 
the SELECT  *  from USER_CONSTRAINTS the WHERE table_name = ' table name in uppercase ' ; 
query results show the type of constraint, the constraint name does not appear on the constraints which field 

/ * query fields in a table constraint * / 
SELECT  *  from USER_CONS_COLUMNS WHERE table_name = ' table uppercase ' ; 
search-result display constraint names, field names, does not show the constraint type 

/ * query constraint primary key of a table * / 
SELECT   A.column_name, A.constraint_name from USER_CONS_COLUMNS a , B USER_CONSTRAINTS
 WHERE A.constraint_name =B.constraint_name and A.table_name = ' table uppercase '  and B.constraint_type = ' P ' ; 
search-result display column names, constraint name. ' P ' represents a Primary Key , ' C ' represents a check, where constraint_type = ' P '

2, to increase the master key

ALTER  Table table the Add  constraint primary key name Primary  Key (column names);

3 , delete the primary key

/ * Primary key can be obtained at the query * / 
the ALTER  the Table table name drop  constraint A primary key

4, modify the primary key

oracle can not directly modify the primary key, and then increase by deleting the existing primary key to achieve the purpose of modification