SQL里面的嵌套查詢語句怎么寫？1，簡單子查詢；select name，age from person where age > ( select age from person wh

SQL里面的嵌套查詢語句怎么寫？

1，簡單子查詢；select name，age from person where age > ( select age from person where name = "孫權(quán)")2，in嵌套查詢；select name from person where countryid in ( select countryid from country where countryname = "魏國")3，some嵌套查詢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嵌套查詢select name from person where countryid > all　　 --當(dāng)countryid大于以下返回的所有id，此結(jié)果才為True，此結(jié)果才返回( select countryid from country where countryname = "魏國")5，exits嵌套查詢SELECT * FROM PersonWHERE exists( SELECT 1 --SELECT 0 SELECT NULL 返回結(jié)果都一樣，因為這三個子查詢都有結(jié)果集返回，因此總是True SELECT * FROM Person照常執(zhí)行)　但是如果子查詢中因為加了條件而沒有結(jié)果集返回，則主語句就不執(zhí)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(jié)果集返回，主語句不執(zhí)行)