What is ROWID and ROWNUM in SQL with Examples? |
您所在的位置：网站首页 › sqlserver rowid › What is ROWID and ROWNUM in SQL with Examples? |
What is ROWID and ROWNUM in SQL with Examples?
|
In this article I would like聽 to explain ‘What is ROWID and ROWNUM in SQL?’. Pseudocolumns are actually associated with the table data but it has nothing to do with table data.ROWID & ROWNUM are Pseudocolumns which are not actual columns in the table but behave like actual columns. You can select the values from Pseudocolumns like ROWID & ROWNUM.ROWID & ROWNUM are very important Pseudocolumns in oracle which is used in data retrieval. CLICK HERE TO GET 20 MOST IMPORTANT COMPLEX SQL QUERIES.. Pseudocolumns are nothing but logical columns which behaves like a physical columns in database.  聽 聽 聽 聽 聽 聽 聽 聽 Rowid and Rownum in SQL
What is ROWID?
ROWID is nothing but the physical memory location on which that data/row is stored.ROWID basically returns address of row.
ROWID uniquely identifies row in database.
ROWID is combination of data object number,data block in datafile,position of row and datafile in which row resides.
ROWID is 16 digit hexadecimal number whose datatype is also ROWID Or UROWID
The fastest way to access a single row is ROWID
ROWID is unique identifier of the ROW.
CLICK HERE TO GET 20 IMPORTANT QUESTIONS ON PERFORMANCE TUNING Example:- select rowid from dual; AAAAECAABAAAAgiAAA What is ROWNUM? ROWNUM is magical column in Oracle which assigns the sequence number to the rows retreives in the table. To limit the values in the table you can use rownum pseudocolumn ROWNUM is nothing but logical sequence number given to the rows fetched from the table. ROWNUM is logical number assigned temporarily to 聽the physical location of the row. You can limit the values in the table using rownum ROWNUM is also unique temparary sequence number assigned to that row.Example: Select Rownum from dual; Answer- 1 So in above article we have dicussed the difference between ROWID & ROWNUM.Following is the difference between ROWID & ROWNUM in tabular format: 聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽ROWID 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽ROWNUM聽 1.ROWID is nothing but Physical memory allocation2.ROWID is permanant to that row which identifies the address of that row. 3.ROWID is 16 digit Hexadecimal number which is uniquely identifies the rows. 4.ROWID returns PHYSICAL ADDRESS of that row. 5. ROWID is automatically generated unique id of a row and it is generated at the time of insertion of row. 6. ROWID is the fastest means of accessing data. 1.聽ROWNUM is nothing but the sequence which is allocated to that data retreival bunch.2.聽ROWNUM is tempararily allocated sequence to the rows. 3.ROWNUM is numeric sequence number allocated to that row temporarily. 4.ROWNUM returns the sequence number to that row. 5. ROWNUM is an dynamic value automatically retrieved along with select statement output. 6.ROWNUM is not related to access of data. Hope you like this article on聽What is ROWID and ROWNUM in SQL? . Kindly comment if any suggestions . CLICK HERE TO GET 20 SQL INTERVIEW QUESTIONS FOR FRESHER..聽 HOME |
【本文地址】