1.oracle: 1.1 增:insert into 删:delete from 改:update tablename set 查:select * from 1.2 聚合函数 max,min,avg,ceil,floor,round 1.3 order by:必须要写在sql语句的最后(where之后) group by:如果使用group by,在select后就必须要有该字段,而且group by不能和where连用,只能和having连用 1.4 多表联查 left join:以左表为