1One or the other (but not both) 异或逻辑运算
select name ,population ,area from world
where (case when population>250000000 then
area<3000000 else area>3000000 end)
2ROUND 小数位
ROUND(gdp/population,2) 两位小数
ROUND(gdp/population,-3) 靠近1000 Round this value to the nearest 1000.
3包含字符个数
LENGTH(name) - LENGTH(REPLACE(name,'a',''))=1 包含a等于 1
4字符串包含单引号
select * from nobel
where winner = 'EUGENE O''NEILL'; 用两个单引号替代单引号