WHERE name LIKE 'A%' -- any name begins with A
WHERE name LIKE 'A_' -- same, but only 2 letters

WHERE grade >= 80 AND grade <=90;
WHERE grade BETWEEN 80 AND 90;

WHERE grade BETWEEN 80 AND 90 AND class = 1;

WHERE grade BETWEEN 80 AND 90 AND
(class = 1 or class = 2);
WHERE grade BETWEEN 80 AND 90 AND
(class IN (1,2));

Boolean operator

• and, or, not
• <, <=, >, >=, =, <>
• like, ilike (不区分大小写)
• between .. and ..
• is null, is not null

Rules

• = 是精确匹配运算符，只有当字段的值完全等于右侧字符串时才为真。
• LIKE 是模式匹配运算符，支持使用通配符：
  • % 表示任意长度（包括 0）的任意字符序列
  • _ 表示任意单个字符

Property

• the result of any comparison including null is unknown
• result of where is false if it evaluates to unknow

set

where name not in (merrick, jack)

select name from instructor
where salary>some(select salary from instructor where dept_name = 'biology')

=some() 和 in() 是等价的

≠all 和 not in 是等价的

empty test