Answer / dinesh a.

You can assing only one primary key on a table , so you
can't modify directoly one column to another , you need to
drop first one then create on another attribute.

SQL>ct constraint_name,constraint_type from user_constraints
where table_name='EMP' and constraint_type='P';

CONSTRAINT_NAME C
------------------------------ -
SYS_C00125220 P

SQL> alter table emp drop constraint SYS_C00125220;

sql> alter table any_table add constraint my_cons_nm
primary key(column_of_tab)

Answer / chandana

YOU CANNOT CHANGE THE CONSTRAINTS DIRECTLY ON A COLUMN.
FIRST DROP THE CONSTARINT U HAVE CREATED AND THEN USE ALTER
COMMAND TO ADD CONSTARINT TO THE CORRECT COLUMN.

Answer / manvendra

ALTER TABLE TABLE_NAME
MODIFY COLUMN (COLUMN2 PRIMARY KEY);

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