Oracle groups fetch the first data in each group, and oracle groups

Oracle groups fetch the first data in each group, and oracle groups
Obtain the first data in each group after grouping in oracle.

[SQL] SELECT * FROM (SELECT ROW_NUMBER () OVER (PARTITION BY x ORDER BY y DESC) rn, test1. * FROM test1) WHERE rn = 1;

After grouping, oracle extracts the first few pieces of data in each group.

After grouping, oracle extracts the first few data entries in each group: SELECT * FROM (field name of the SELECT group, ROW_NUMBER () OVER (partition by field name of the grouping order) as rnfrom table name) where rn <= 10 ??

How to obtain the first few pieces of data from each group in an SQL group?

Select * from table name a where exists (select top 2 * from
(Select a, a1, a2 from table name group by a, a2) B where a. a = B. a and a. a2 = B. a2)