user: Question: What is the enrollment of STM which has been in competition since 1990?
Columns: ['School', 'Location', 'Enrolment', 'Founded', 'Denomination', 'Day/Boarding', 'School Colours', 'Abbreviation', 'In competition since']
Types: ['text', 'text', 'real', 'real', 'text', 'text', 'text', 'text', 'real']
Sample row: ["All Hallows' School", 'Brisbane', 1300.0, 1861.0, 'Catholic', 'Day', 'Light Blue & White', 'AHS', 1990.0]
SQL:

assistant: SELECT "Enrolment" FROM "Table" WHERE "In competition since" = 1990.0 AND "Abbreviation" = 'STM';