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比较运算符

用于比较一个或多个表达式的布尔运算符。

`相等 (=)`

SELECT last_name l FROM "test_emp" WHERE emp_no = 10000 LIMIT 5;

`空值安全相等 (<=>)`

SELECT 'elastic' <=> null AS "equals";

    equals
---------------
false

SELECT null <=> null AS "equals";

    equals
---------------
true

`不等 (<> 或 !=)`

SELECT last_name l FROM "test_emp" WHERE emp_no <> 10000 ORDER BY emp_no LIMIT 5;

`比较 (<, <=, >, >=)`

SELECT last_name l FROM "test_emp" WHERE emp_no < 10003 ORDER BY emp_no LIMIT 5;

`BETWEEN`

SELECT last_name l FROM "test_emp" WHERE emp_no BETWEEN 9990 AND 10003 ORDER BY emp_no;

`IS NULL/IS NOT NULL`

SELECT last_name l FROM "test_emp" WHERE emp_no IS NOT NULL AND gender IS NULL;

`IN (<值1>, <值2>, ...)`

SELECT last_name l FROM "test_emp" WHERE emp_no IN (10000, 10001, 10002, 999) ORDER BY emp_no LIMIT 5;