SELECT product_name,sale_price
FROM PRODUCT AS P
WHERE EXISTS (SELECT * FROM SHOPPRODUCT AS SP
WHERE SP.shop_id = ‘00C’ AND SP.product_id = P.product_id);
其中PRODUCT表示商品表,SHOPPRODUCT指商店在售商品表,其中shop_id字段表示商店id,product_id表示产品id。
以上这段sql主要是完成了哪个操作?