When we substitute in text for a ${var} in a database query, we have to provide special handling for escape characters. For a simple example, say you have select="select * from employees where name like '${var}' " and var is "O'Malley". If we did not escape the ' in O'Malley then the select would end up as "select * from employees where name like 'O'Malley' " which is a malformed select.

However, the problem also exists where you can have "select FIRST_NAME from EMPLOYEES" and _ is a special character in Sql Server. To handle this situation if the name of your var starts with an underscore, such as ${_var}, then no escape substitution is performed.

The escape characters handled are:

DB2
'	''
"	""
_	\_
?	\?
%	\%
\	\\

MySql
'	\'
"	\"
_	\_
%	\%
\	\\

Oracle
'	''
%	\%
\	\\

Sql Server
'	''
[	[[]
%	[%]
_	[_]

additional keywords: parameter, parameters