带条件过滤 WHERE

带条件过滤 WHERE要点

• 比较运算符涵盖等于、不等于、大于、小于、大于等于、小于等于
• 逻辑 AND / OR / NOT，混用务必加括号，优先级 NOT 最高
• 范围用 BETWEEN 小 AND 大，集合用 IN (值1, 值2)
• 空值用 IS NULL / IS NOT NULL，NULL 不能用等于判断
• 模糊用 LIKE '%词%'，% 匹配任意长度，_ 匹配单字符
• 条件越精确越能走索引，全表扫的 WHERE 会很慢

带条件过滤 WHERE示例

						SELECT * FROM product
						WHERE price BETWEEN 100 AND 99999
						  AND created_at BETWEEN '2026-01-01' AND '2099-12-31'
						  AND name LIKE '键盘%';

						SELECT * FROM product WHERE id IN (1, 3, 5);
						SELECT * FROM product WHERE price IS NOT NULL;

查询数据知识点