These posts from the Forums contain a wealth of information and references for people who are just starting out as a Tessitura DBA:
https://community.tessituranetwork.com/tessitura_software_forums/f/tessitura_technical-9/27607/learning-sql
https://community.tessituranetwork.com/tessitura_software_forums/f/tessitura_technical-9/14632/first-step-in-custom-reports/44992
https://community.tessituranetwork.com/tessitura_software_forums/f/tessitura_technical-9/10187/report-writing/31461