The Database rowid and rownum pseudo columns

The Database rowid and rownum are the important pseudo columns that can be used and helpful in query writing.

Database rowid:

• It is automatically generated unique id of a row and it is generated at a time of row inserts in a table 
• It is a physical address of the rows.
• A rowid is permanent
• A rowid is 16-bit hexadecimal
• A rowid gives address of rows or records
• A rowid is the fastest means of accessing data.

Database rownum:

• It is a sequential number assigned (by database) to each returned row during query execution.
• It is temporary and numeric
• It gives count of records
• It is an dynamic value automatically retrieved along with select statement output.
• It represents the sequential order in which Oracle has retrieved the row.

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