思路1
用左联结。注意处理NULL不能用=,NULL=NULL是false。NULL 和任何值比较都是false
判断是不是NULL必须用 is null
or is not null
SELECT e.name, b.bonus
FROM Employee e LEFT JOIN Bonus b
ON e.empId=b.empId
WHERE b.bonus < 1000 OR b.bonus IS NULL;
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用左联结。注意处理NULL不能用=,NULL=NULL是false。NULL 和任何值比较都是false
判断是不是NULL必须用 is null
or is not null
SELECT e.name, b.bonus
FROM Employee e LEFT JOIN Bonus b
ON e.empId=b.empId
WHERE b.bonus < 1000 OR b.bonus IS NULL;
Last updated
Was this helpful?