ISO/ANSI SQL:
SELECT * FROM TableName FETCH FIRST 20 ROWS ONLY;
MySQL; PostgreSQL; SQLite:
SELECT * FROM TableName LIMIT 20; 
Oracle:
SELECT Id,
   Col1
FROM (SELECT Id,
           Col1,
           row_number() over (order by Id) RowNumber
      FROM TableName)
WHERE RowNumber <= 20
SQL Server:
SELECT TOP 20 * 
FROM dbo.[Sale]