数据库-null值和notnull操作
null和not null值对一些字段类型要进行检查，判断某些字段是否为NULL，或者 non-NULLmysql> SELECT name, birth, death, ‐> TIMESTAMPDIFF(YEAR,birth,death) AS age ‐> FROM pet WHERE death IS NOT NULL ORDER BY age; +‐‐‐...
