ALTER TABLE SQL Oracle – 12c

we are confused with below answers.so our answer is 3, 5

Which three actions can you perform by using the ALTER TABLE command?

1- Lock a set of rows in a table.

2- Drop pseudocolumns from a table.

3- Rename a table.

4- Drop all columns simultaneously from a table.

5- Enable or disable constraints on a table.

6- Restrict all DML statements on a table.

Thank you

Answer

3, 5 and 6

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1. Lock a set of rows in a table.

   Oracle locks rows it is performing DML on or when you use SELECT ... FOR UPDATE; you cannot lock rows with ALTER TABLE.

2. Drop pseudocolumns from a table.

   The common pseudocolumns of a table are ROWID, ROWNUM and ORA_ROWSCN; you cannot drop these.

3. Rename a table.

   CREATE TABLE table_name ( a NUMBER, b NUMBER );
   ALTER TABLE table_name RENAME TO other_name;
   

   Works.

4. Drop all columns simultaneously from a table.

   CREATE TABLE table_name ( a NUMBER, b NUMBER );
   ALTER TABLE table_name DROP ( a, b );
   

   Outputs:

   ORA-12983: cannot drop all columns in a table
   

5. Enable or disable constraints on a table.

   CREATE TABLE table_name ( a NUMBER CONSTRAINT qu5__pk PRIMARY KEY, b NUMBER );
   ALTER TABLE table_name MODIFY PRIMARY KEY DISABLE;
   

   Will disable the constraint.

6. Restrict all DML statements on a table.

   CREATE TABLE table_name ( a NUMBER, b NUMBER );
   ALTER TABLE table_name READ ONLY;
   

   Then

   INSERT INTO table_name ( a, b ) VALUES ( 1, 1 );
   UPDATE table_name SET b = 2;
   DELETE FROM table_name;
   

   all fail with the exception:

   ORA-12081: update operation not allowed on table "SCHEMA_NAME"."TABLE_NAME"
   

db<>fiddle here