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<\/p>\nIn today’s article, we will learn how to delete data from a table and the differences between DELETE and TRUNCATE commands.<\/p>\n
Data from a table can be deleted with DELETE and TRUNCATE commands. But there are differences between them.<\/p>\n
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By default, Oracle deals (deallocates) the space held by the table with the TRUNCATE operation.<\/p>\n
If we do not want the space held by the table to be released, we must perform the TRUNCATE operation with the word “REUSE STORAGE”.<\/p>\n
In this way, Oracle is not busy with the field allocation process while new records are inserted into the table.<\/p>\n
SQL> TRUNCATE TABLE ACCOUNT REUSE STORAGE;\r\n\r\nTable truncated.<\/pre>\nHigh-Water Mark:<\/strong> The border between used and unused areas within a segment is called the high-water mark of the table.<\/p>\n
Before data is inserted into a new table, no blocks are used and the high-water mark is zero.<\/p>\n
When large volumes of data are deleted with DELETE, Oracle will scan every block even if there is no data in the table, since the high-water mark will not change.<\/p>\n
This is a serious performance problem that appears as a “full-table scan”.<\/p>\n
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