A.選擇、投影B.選擇、乘C.投影、乘D.選擇、投影、乘
A.關(guān)系模型B.層次模型C.網(wǎng)絡(luò)模型D.實(shí)體-聯(lián)系模型
A.AGE〉18 AND AGE〈24B.AGE〉=18 AND AGE〈24C.AGE〉18 AND AGE〈=24D.AGE〉=18 AND AGE〈=24