What is rowID & rowNum (ROWID vs ROWNUM)

Question

I'd like to know difference between rowID and rowNUM

And how to see both of these in our table.

when I execute this:

SELECT * FROM emp WHERE rownum=1

It returns one query but when I do the same for rowid it says

inconsistent datatypes: expected ROWID got NUMBER

And even in some of the tables, rownum returns null . Why so?

Please clarify this: rowid vs rownum?(Demo query)

Thank you

EDIT: Require to use alias to display ROWID and ROWNUM(as they're pseudocolumn) like:

SELECT rownum r1, rowid r2 FROM emp

Oni

"No such column is there in the table" doesn't sound like an oracle error. How are you running these queries? – Ester

@Mureinik, I'm running these queries over W3schools for now. But even oracle doesn't support rownum – Oni

FYI - Use sqlfiddle.com to play around. – Delores

Answer 1

Both, ROWNUM and ROWID are pseudo columns.

Rowid

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

An example query would be:

SELECT ROWID, last_name  
   FROM employees
   WHERE department_id = 20;

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

Rownum

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

You can limit the amount of results with rownum like this:

SELECT * FROM employees WHERE ROWNUM < 10;

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

Difference

The actual difference between rowid and rownum is, that rowid is a permanent unique identifier for that row. However, the rownum is temporary. If you change your query, the rownum number will refer to another row, the rowid won't.

So the ROWNUM is a consecutive number which applicable for a specific SQL statement only. In contrary the ROWID, which is a unique ID for a row.

Orthoclase

Answer 2

Rownum (numeric) = Generated Sequence Number of your output.
Rowid (hexadecimal) = Generated automatically at the time of insertion of row.

SELECT rowid,rownum fROM EMP


ROWID ROWNUM                 
----- ---------------------- 
AAAR4AAAFAAGzg7AAA, 1                      
AAAR4AAAFAAGzg7AAB, 2                      
AAAR4AAAFAAGzg7AAC, 3                      
AAAR4AAAFAAGzg7AAD, 4                      
AAAR4AAAFAAGzg7AAE, 5      

Watteau

Joel: How to qualify the RowID as oracle's generated RowID if EMP has also an RowID field? – Lareine

this query not working in MYSQL. Error Code: 1054. Unknown column 'rowid' in 'field list' 0.000 sec – Leggy

Answer 3

1. Rowid gives the address of rows or records. Rownum gives a count of records
2. Rowid is permanently stored in the database. Rownum is not stored in the database permanently
3. Rowid is automatically assigned with every inserted into a table. Rownum is a dynamic value automatically retrieved along with select statement output.
4. It is only for display purpose.

Nona

Answer 4

row id shows the unique identification for row rownum shows the unique default series of 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)

Desiderata