How many cellos are suggested in the reference with section size for 20 players?
CREATE TABLE "suggested_string_section_sizes" (
  "reference" text,
  "author" text,
  "section_size" text,
  "violins" real,
  "violas" real,
  "celli" real,
  "basses" real
);
SELECT "celli" FROM "suggested_string_section_sizes" WHERE "section_size"='20 players';