1，簡單子查詢；select name,age from person where age > ( select age from person where name = "孫權")2，in巢狀查詢；select name from person where countryid in ( select countryid from country where countryname = "魏國")3，some巢狀查詢select name from person where countryid = some 　　　　　　--用等號和以下查詢到的值比較，如果與其中一個相等，就返回( select countryid from country where countryname = "魏國")4，all巢狀查詢select name from person where countryid > all　　 --當countryid大於以下返回的所有id，此結果才為True，此結果才返回( select countryid from country where countryname = "魏國")5，exits巢狀查詢SELECT * FROM PersonWHERE exists( SELECT 1 --SELECT 0 SELECT NULL 返回結果都一樣，因為這三個子查詢都有結果集返回，因此總是True SELECT * FROM Person照常執行)　但是如果子查詢中因為加了條件而沒有結果集返回，則主語句就不執行了：SELECT * FROM PersonWHERE exists( SELECT * FROM Person WHERE Person_Id = 100 --如果不存在Person_Id的記錄，則子查詢沒有結果集返回，主語句不執行)