Using Escape character in Oracle

In Oracle the '_' character is used to match exactly one character, wherease '%' is used to match zero or more occurrences of any characters. For example if we need to search a string in Oracle with '_' prsence in the column, then in such cases normal LIKE operator will not work. We need to escape the character '_'.

Here is the syntax for escaping the character in Oracle

SELECT name FROM emp WHERE id LIKE '%/_%' ESCAPE '/';

Oracle: Difference between Rank and Dense_Rank

RANK leaves gaps while ranking the records whereas DENSE_RANK doesn't leave any gaps. For eg, if we have a tie at the 4th position and there are 2 records with the same value then

RANK - will place both the records in the 4th position, and will have the next record at the 6th position (leaving a gap of 1 position)

DENSE_RANK - will also place both the records in the 4th position, but the next record will be placed at 5th position (no gap will be placed).