The mysql database is converted into a pit that oracle has stepped on

1. To use a group function such as count, it must be used in conjunction with group by. The acquired fields either appear in the group function or in group by.
2. Oracle uses union not only to have the same field name and the same data type
3.REGEXP_LIKE (name, '.+*aa.+*') Regularly use .+* instead of %
4. Field is strictly case
5.case when a='1'then 'xxxx' when a='2' then 'ssss' else 'zzzzz' end