The project uses tempate for writing report generation code. please refer the file gather_report.tpl.html The AWK script apply_template.awk is used for generating the report.sql (or ../gather_report.sql)

cat gather_report.tpl.html | awk -f apply_template.awk  > report.sql; psql -X -f report.sql > out.html  

Please refer SQL documentation on SQL statement used in this project.