Three ways to delete data by Oracle

Three ways to delete data by Oracle

Statement delete-truncate-drop

drop command

drop table Table name;

For example: Delete student table (student)
drop table student；

Notice:
1. UsedropDeleting table data not only deletes the data in the table, but also deletes the structure!

truncate command

truncate  tableTable name;

For example: Delete student table (student)
truncate table student；

Notice:
1. UsetruncateDelete table data, just delete the data in the table, the table structure will not be deleted!
2. When deleting data from the entire table, the process is the system to delete data at one time, which is relatively efficient
        3、truncateDelete free space

delete command

delete fromTable name;

For example: Delete student table (student)
delete from student；

Notice:
1. UsedeleteDelete table data, just delete the data in the table, the table structure will not be deleted!
2. Although it also deletes the data of the entire table, the process is the system's row by row, which is more efficient thantruncateLow
        3、deleteDeletion does not release space

A little summary about truncate:

The truncate table is functionally the same as the delete statement without the where clause: both delete all rows in the table.

But truncate is faster than delete and uses fewer system and transaction log resources.

The delete statement deletes one line at a time and records one item for each line deleted in the transaction log. Therefore, you can rollback the delete operation.

1. Truncate is very fast on various tables, whether large or small. If there is a rollback command delte will be revoked, and truncate will not be revoked.

2. truncate is a DDL language. Like all other DDL languages, it will be implicitly submitted and cannot use the rollback command for truncate.

3. truncate will reset the high-level line and all indexes. When you fully browse the entire table and index, the table after the truncate operation is much faster than the table after the delete operation.

4. Truncate cannot trigger any delete trigger.

5. When the table is cleared, the index of the table and the table will be reset to the initial size, but delete cannot.

6. Cannot clear the parent table