CREATE TABLE "united_states" (
  "name" text,
  "level" real,
  "digits" real,
  "average_size_square_miles" text,
  "number_of_h_us_approximate" real,
  "example_name" text,
  "example_code_huc" real
);

Question: What is the mean huc example code when the example name's lower snake, there are 6 digits, and less than 3 levels?
SQL: SELECT AVG("example_code_huc") FROM "united_states" WHERE "example_name"='lower snake' AND "digits"=6 AND "level"<3;

Question: What's the approximate number of HUs when there are more than 2 digits, and 6 levels?
SQL: SELECT COUNT("number_of_h_us_approximate") FROM "united_states" WHERE "digits">2 AND "level"=6;

Question: How many HUC example codes have 1 level?
SQL: SELECT COUNT("example_code_huc") FROM "united_states" WHERE "level"=1;

Question: What is the mean level number when the example name is lower snake and the approximate number is hus is less than 370?
SQL: SELECT AVG("level") FROM "united_states" WHERE "example_name"='lower snake' AND "number_of_h_us_approximate"<370;