SQL query for top 5 results without the use of LIMIT/ROWNUM/TOP

Question

如何在不使用LIMIT / ROWNUM / TOP的情况下从有序结果集中选择前5个条目，具体取决于DBMS？

Answer 1

Standard ANSI SQL solution:

SELECT *
FROM ( 
    SELECT col1, 
           col2,
           row_number() over (order by some_col) as rn
    FROM the_table
) t
WHERE rn <= 5

Works in Oracle, PostgreSQL, DB2, SQL Server, Sybase, Teradata and the upcoming Firebird 3.0 but not in MySQL as it still doesn't support windowing functions.