A database is queried with on demand database query reduction A query document includes global variables selectively set off by first tags identifying a first global variable as a complete replacement variable and by second tags identifying a second global variable as a complete removal string. An agent is provided for building from the query document an expanded query by replacing any variables set off by first tags with runtime strings, setting off any unions in the query document, and selectively replacing any variables set off by second tags and removing the second tags without replacing variables set off by second tags.