Conditional SQL in Cognos by using prompt values to control line commenting

Here's a technique that allows the omission of certain sections of SQL in response to prompt values in Cognos Report Studio:

1 #join('|',substitute(prompt('Prompt','token','Excl'),'',grep(prompt('Prompt','token','Excl'),array('Incl', 'Excl /* '))))#

2 And column_name is not null 
3 #join('|',substitute(prompt('Prompt','token','Excl'),'',grep(prompt('Prompt','token','Excl'),array('Incl', 'Excl */ '))))# 

The prompt named Prompt has two values, Incl and Excl.

When the prompt value is 'Excl' the grep macro in line 1 returns the array element 'Excl /* '. The substitute macro replaces the array element with an array element containing ' /* '. The join macro converts the array element to a  string. /* is used as the start of a comment block in Cognos.

Line 3 resolves to */ when the prompt value is 'Excl' thus commenting out line 2 entirely.