The Purpose of Deleting Data
When using an Oracle database, there are times when it is necessary to remove data from a table. There are two ways of removing data: deleting or truncating. It is important to understand the difference between these two methods so that the appropriate one can be used for the situation at hand.Delete vs. Truncate Statement
The DELETE statement is used when you want to selectively remove rows from a table based on a certain condition or set of conditions. This means that you can specify which rows to delete, and those that don't satisfy the specified condition will be left in the table. However, the TRUNCATE statement is used when you want to remove all the rows from a table. It is an efficient method of removing all the data from a table, since it does not require the same level of undo or redo processing that a DELETE statement would need.Differences in Usage and Impact
When deciding whether to use a DELETE or TRUNCATE statement, there are several factors to consider. One is the size of the table. A DELETE statement may take a long time to execute if the table is large, since all the rows that match the specified condition must be located and deleted. In contrast, a TRUNCATE statement will remove all the rows from the table in one step, regardless of size. However, a TRUNCATE statement cannot be used if the table is a parent table in a referential integrity relationship. Another factor to consider is the impact that the statement will have on database space. When a DELETE statement is executed, the rows that are deleted are not immediately removed from the database - they are marked for deletion and will be removed by the automatic space management system at a later time. This means that the space that the rows occupied is still reserved for them. On the other hand, when a TRUNCATE statement is executed, all the space that was used by the rows is immediately released back to the database. This can be an important consideration when dealing with large tables. In conclusion, when using an Oracle database, it is important to understand the differences between DELETE and TRUNCATE statements. While both can be used to remove data from a table, they differ in the scope of what they remove and the impact they have on the database. By carefully considering the situation at hand and the factors involved, making the right choice can help to ensure the integrity and performance of the database over the long term.
