CREATE TABLE "first_conversion_period_1867_1887" (
  "class" text,
  "railway_number_s" text,
  "quantity_rebuilt" real,
  "rebuild_year_s" text,
  "type" text
);

Question: What's the railway number of a D(rebuild) class?
SQL: SELECT "railway_number_s" FROM "first_conversion_period_1867_1887" WHERE "class"='d(rebuild)';

Question: What the least quantity having a T2A class?
SQL: SELECT MIN("quantity_rebuilt") FROM "first_conversion_period_1867_1887" WHERE "class"='t2a';