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How to handle percent (%) underscore (_) and quotes within SQL LIKE queries

Oracle Tips by Burleson Consulting
January 8, 2008

Question:  I am getting unexpected results when trying to prefix wildcards (% and _) with an escape character in a LIKE clause.  I also have quotes within the LIKE string, and I need SQL to treat these as literal quotes and not as string terminators.  How does Oracle manage these special characters within SQL queries?

Answer:  Oracle handles special characters with the ESCAPE clause, and the most common ESCAPE is for the wildcard percent sign (%), and the underscore (_).  For handling quotes within a character query, you must add two quotes for each one that is desired.  This will display "Larry's the Man!":

select 'Larry''s the Man!' from dual;

Most Oracle professionals use the UNIX escape character "\" backslash, but you can define any escape character that you desire in SQL*Plus. 

For an example using underscores, this query wants to display all values that contain the string "_to_" (e.g. hard_to_get within a query).  Here, we must escape the underscore:

set escape '\'
select stuff from mytab
where
   mycol like '%\_to\_%';
 
Or:
 
select stuff from mytab
where
   mycol like '%\_to\_%' escape '\';
 
For another example, assume that we want to seek columns that contain a percent sign (%).  Here we must leave the front and % while escaping the middle percent sign:
 
where
   mycol like '%\%%';
 
 
For more details and examples of scripts using escape characters, see these notes:
 
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