CREATE TABLE ref_characteristic_types (characteristic_type_code CLOB, characteristic_type_description CLOB)
CREATE TABLE products (product_id NUMBER, color_code CLOB, product_category_code CLOB, product_name CLOB, typical_buying_price CLOB, typical_selling_price CLOB, product_description CLOB, other_product_details CLOB)
CREATE TABLE characteristics (characteristic_id NUMBER, characteristic_type_code CLOB, characteristic_data_type CLOB, characteristic_name CLOB, other_characteristic_details CLOB)
CREATE TABLE ref_product_categories (product_category_code CLOB, product_category_description CLOB, unit_of_measure CLOB)
CREATE TABLE product_characteristics (product_id NUMBER, characteristic_id NUMBER, product_characteristic_value CLOB)
CREATE TABLE ref_colors (color_code CLOB, color_description CLOB)

Return the unit of measure for 'Herb' products.
SELECT unit_of_measure FROM ref_product_categories WHERE product_category_code = "Herbs"
SELECT "unit_of_measure" FROM "ref_product_categories" WHERE "Herbs" = "product_category_code"