Escape Characters in Oracle PL/SQL Queries

Oracle databases reserve some special characters with specific meaning and purpose within Oracle environment. These reserved characters include _ (underscore) wild card character which used to match exactly one character, % (percentage) which used to match zero or more occurrences of any characters and ‘ (apostrophe or quotation mark) which used to mark the value supplied. These special characters will not be interpreted literally when building SQL query in Oracle, and may cause error in results returned especially when performing string search with LIKE keyword. To use these characters so that Oracle can interpret them literally as a part of string value instead of preset mean, escape character has to be assigned.

Oracle allows the assignment of special escape characters to the reserved characters in Oracle can be escaped to normal characters that is interpreted literally, by using ESCAPE keyword.

For example, to select the name of guests with _ (underscore) in it, use the following statement:

SELECT guest_name FROM guest_table WHERE name LIKE ‘%\_%’ ESCAPE ‘\’;

Without specifying the \ (backslash) as escape clause, the query will return all guest names, making the unwanted results problem.

The above syntax will not work on ‘ (quote). To escape this quotation mark and to display the quote literally in string, insert another quote (total 2 quotes) for every quote that want to be displayed. For example:

SELECT ‘This will display line with quote’’s word.’ FROM dual;

Output: This will display line with quote’s word.