一.数据过滤
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1.通配符 - 下划线（ _ ）
SELECT * FROM milk_tea AS m WHERE m.prod_name LIKE '奶_';
SELECT * FROM milk_tea AS m WHERE m.prod_name LIKE '薯_';
SELECT * FROM milk_tea AS m WHERE m.prod_name LIKE '方_面';
SELECT * FROM milk_tea AS m WHERE m.prod_name LIKE '方__';
SELECT * FROM milk_tea AS m WHERE m.prod_name LIKE '奶_糖';
SELECT * FROM milk_tea AS m WHERE m.prod_name LIKE '__糖';
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2.通配符 - 百分号（ % ）
SELECT * FROM milk_tea AS m WHERE m.prod_name LIKE '%糖';
SELECT * FROM milk_tea AS m WHERE m.prod_name LIKE '方%面';
SELECT * FROM milk_tea AS m WHERE m.prod_name LIKE '方便%面';
SELECT * FROM milk_tea AS m WHERE m.prod_name LIKE '奶%';
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3.“且”操作 - AND
SELECT * FROM milk_tea AS m WHERE m.sale_price >= 5;
SELECT * FROM milk_tea AS m WHERE m.sale_price <= 15;
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SELECT * FROM milk_tea AS m WHERE m.sale_price >= 5 AND m.sale_price <= 15;
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SELECT * FROM milk_tea AS m WHERE m.sale_price >= 5 AND m.sale_price <= 15 AND m.sale_price IS NOT NULL;
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SELECT * FROM milk_tea AS m WHERE m.sale_price >= 5 AND m.sale_price <= 15 AND m.prod_name LIKE '薯_';
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4.“或”操作 - OR
SELECT * FROM milk_tea AS m WHERE m.sale_price >= 5 OR m.sale_price <= 15;
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SELECT * FROM milk_tea AS m WHERE m.sale_price >= 5 AND m.sale_price <= 15 OR m.sale_price BETWEEN 1 AND 5;
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SELECT * FROM milk_tea AS m WHERE m.sale_price >= 5 AND m.sale_price <= 15 OR m.sale_price IS NULL;
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SELECT * FROM milk_tea AS m WHERE m.prod_name = '奶茶' OR m.prod_name = '薯片' OR m.prod_name = '棒棒糖';
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5.取值限制 - IN
SELECT * FROM milk_tea AS m WHERE m.prod_name IN ('奶茶','薯片','棒棒糖');
SELECT * FROM milk_tea AS m WHERE NOT m.prod_name IN ('奶茶','薯片','棒棒糖');
SELECT * FROM milk_tea AS m WHERE m.in_price IN (10.8, 2.1, 9.3);
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6.否定条件 - NOT
SELECT * FROM milk_tea AS m WHERE NOT m.prod_name IN ('奶茶','薯片','棒棒糖');
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SELECT * FROM milk_tea AS m WHERE NOT m.prod_name = '奶茶' AND NOT m.prod_name = '薯片';
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二.课后作业
Q1：写出 SQL 语句中的通配符，及其用法。
答：1.下划线_：代表任意字符，且能代表的字符数仅为1。必须知道要代表的字符具体的位置。
2.百分号%：代表任意字符，且能代表的字符数为任意多个，包括0。
Q2：写出模糊查询的具体结构。
答：关键字（WHERE）+ 查询的列（字段名）+ 关键字（LIKE）+ ‘匹配文本’（含通配符）
Q3：写出以下语句。
1、从 milk_tea 表中找到产品名是‘薯’开头或者‘糖’结尾的。
2、从 milk_tea 表中找到产品名是‘薯’开头或者‘糖’结尾的，且产品名称只有 2 个字。
3、从 milk_tea 表中找到产品名是‘奶’开头并且‘茶’结尾的。
4、从 milk_tea 表中找到销售价格不大于 10 的产品。（2 种写法）
SELECT * FROM milk_tea;
SELECT m.prod_name FROM milk_tea AS m WHERE m.prod_name LIKE '薯%' OR m.prod_name LIKE '%糖';
SELECT m.prod_name FROM milk_tea AS m WHERE m.prod_name LIKE '薯_' OR m.prod_name LIKE '_糖';
SELECT m.prod_name FROM milk_tea AS m WHERE m.prod_name LIKE '奶%茶';
SELECT m.prod_name FROM milk_tea AS m WHERE m.prod_name LIKE '奶%' AND m.prod_name LIKE '%茶';
SELECT m.* FROM milk_tea AS m WHERE m.sale_price <= 10;
SELECT m.* FROM milk_tea AS m WHERE m.sale_price BETWEEN 0 AND 10;