CREATE TABLE table_203_528 (id NUMBER, "year" NUMBER, "political rights" NUMBER, "civil liberties" NUMBER, "status" CLOB, "president" CLOB)

who was president before mamadou tandja ?
SELECT "president" FROM table_203_528 WHERE id = (SELECT id FROM table_203_528 WHERE "president" = 'mamadou tandja') - 1
SELECT "president" FROM "table_203_528" WHERE "id" = (SELECT "id" FROM "table_203_528" WHERE "president" = 'mamadou tandja') - 1