比較、邏輯、重複查詢
查詢大於指定條件的數據
select * from tb_Student where Score>60;
NOT與謂詞進行組合的查詢
1.NOT BETWEEN
指定值的包含範圍,用and分割開始值和結束值
語法:test_expression [ NOT ] BETWEEN begin_expression AND end_expression
test_expression :這是在 begin_expression 和 end_expression 定義範圍中所要測試的運算是。begin_expression 和 end_expression 的 test_expression 必須是相同的數據類型。
NOT:執行否定運算的謂詞
AND:用於指定範圍
eg:select *from tb_Student where Score [not] between 60 and 80;
2.IS[ NOT ]NULL
指定對空值和非空值的查詢
eg:
3.[NOT] IN
語法:test_expression [ NOT ] IN(subquery,expression[,...n])
test_expression:Sql表達式
subquery:包含結果集的子查詢
expression[,...n]):測試表達式
查詢時不顯示重複的記錄
DISTINCT:
select distinct english from tb_Student;//不顯示英語成績相同的記錄
顯示重複記錄的個數
select count(Score) as 學生人數,id ,name from tb_Student group by Score,id,name having count(Score)>1;