View the Exhibit and examine the structure of the EMP table which is not partitioned and not an index- organized table. Evaluate the following SQL statement:
ALTER TABLE emp
DROP COLUMN first_name;
Which two statements is true regarding the above command? (Choose two.)
A.
The FIRST_NAME column would be dropped provided it does not contain any data.
B.
The FIRST_NAME column would be dropped provided at least one or more columns remain in the table.
C.
The FIRST_NAME column can be rolled back provided the SET UNUSED option is added to the above SQL statement.
D.
The FIRST_NAME column can be dropped even if it is part of a composite PRIMARY KEY provided the
CASCADE option is used.
create table empx as select sal from emp;
desc empx;
ALTER TABLE empx DROP COLUMN sal2;
ALTER TABLE empx add (sal2 number);
ORA-12983: cannot drop all columns in a table
SET UNUSED also works the same way as DROP column
1. At least one column must be retained.
2. CASCADE option can be used
ALTER TABLE table-Name
{
ADD COLUMN column-definition |
ADD CONSTRAINT clause |
DROP [ COLUMN ] column-name [ CASCADE | RESTRICT ]
DROP { PRIMARY KEY | FOREIGN KEY constraint-name | UNIQUE
constraint-name | CHECK constraint-name | CONSTRAINT constraint-name }
ALTER [ COLUMN ] column-alteration |
LOCKSIZE { ROW | TABLE }
}