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Status: published
Programming, Software and application
2020-12-07 03:13:23
ALTER TABLE DROP Column
1809
Introduction to Oracle Database Oracle Tables and Data definition Modifying data Oracle Query and Filter Oracle data types Joining tables Oracle Operators Grouping data Constraints
এই কোর্সে যা থাকছে
৩টি বিষয়
৮০টি লাইভ ক্লাস
Simply, to drop column from a table, we need to use following statement
ALTER TABLE table_name DROP COLUMN column_name;
Many time, if we use above statement to drop column from a big table, it can be time and resource consuming. Therefore, we typically drop the column logically by using the ALTER TABLE SET UNUSED COLUMN statement as follows:
ALTER TABLE table_name SET UNUSED COLUMN column_name;
Once you execute the statement, the column is no longer visible for accessing.
During the off-peak hours, you can drop the unused all columns physically using the following statement:
ALTER TABLE table_name DROP UNUSED COLUMNS;
If you want to reduce the amount of undo logs accumulated, you can use the CHECKPOINT option that forces a checkpoint after the specified number of rows has been processed.
ALTER TABLE table_name DROP UNUSED COLUMNS CHECKPOINT 250;
To drop multiple columns, you use the statement below:
ALTER TABLE table_name DROP ( column_name_1, column_name_2 );