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What are rowID and rowNum (ROWID vs ROWNUM)

I would like to know the difference between rowID and rowNUM

And how to see both of these tables in our table.

when i do this:

 SELECT * FROM emp WHERE rownum=1

It returns a single request, but when I do the same for rowid, it says

inconsistent data types: expected ROWID received NUMBER

And even in some tables, rownum returns null. Why is that?

Clarify this: rowid vs rownum? (Demo request)

thanks

EDIT: It is required to use an alias to display rowID and rowNUM (since they are pseudo- rowNUM ) as:

SELECT rownum r1, rowid r2 FROM emp

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4 answers

Both rownum and rowed are pseudo columns.

Rowid

For each row in the database, the ROWID pseudo-column returns the address of the row.

An example request would be:

 SELECT ROWID, last_name FROM employees WHERE department_id = 20;

More information about rowid here: https://docs.oracle.com/cd/B19306_01/server.102/b14200/pseudocolumns008.htm

Rownum

For each row returned by the query, the ROWNUM pseudo-column returns a number indicating the order in which Oracle selects a row from a table or a set of joined rows. The first row selected has ROWNUM equal to 1, the second has 2, etc.

You can limit the number of results using rownum as follows:

 SELECT * FROM employees WHERE ROWNUM < 10;

More information about rownum here: https://docs.oracle.com/cd/B19306_01/server.102/b14200/pseudocolumns009.htm

difference

The actual difference between rowid and rownum is that the ROWID is a constant unique identifier for this row. However, rownum is temporary. If you change your query, rownum will refer to another row, and rowid will not.

Therefore, ROWNUM is a sequential number that is applicable only to a particular SQL statement. Unlike ROWID, which is a unique identifier for a string.

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Rownum (numeric) = The generated sequence of numbers of your output.
Rowid (hexadecimal) = Created automatically during row insertion.

 SELECT rowid,rownum fROM EMP ROWID ROWNUM ----- ---------------------- AAAR4AAAFAAGzg7AAA, 1 AAAR4AAAFAAGzg7AAB, 2 AAAR4AAAFAAGzg7AAC, 3 AAAR4AAAFAAGzg7AAD, 4 AAAR4AAAFAAGzg7AAE, 5
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  1. Rowid gives the address of rows or records. Rownum gives the number of records
  2. Rowid is permanently stored in the database. Rownum is not permanently stored in the database
  3. Rowid is assigned automatically each time it is added to a table. Rownum is a dynamic value that is automatically retrieved with the output of the select statement.
  4. This is just for demonstration.
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row identifier shows unique identification for row rownum shows a unique series of default numbers.

 select * from emp where rownum<=5; (it will execute correctly and gives output first 5 rows in your table ) select * from emp where rowid<=5; (wrong because rowid helpful to identify the unique value)
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