MAX value of column with corresponding columns - sql-server-2000

Question

I am using an old SQL Server 2000.
Here is some sample data:
ROOMDATE rate bus_id quantity
2018-09-21 00:00:00.000 129 346686 2
2018-09-21 00:00:00.000 162 354247 36
2018-09-21 00:00:00.000 159 382897 150
2018-09-21 00:00:00.000 120 556111 25
2018-09-22 00:00:00.000 129 346686 8
2018-09-22 00:00:00.000 162 354247 86
2018-09-22 00:00:00.000 159 382897 150
2018-09-22 00:00:00.000 120 556111 25
2018-09-23 00:00:00.000 129 346686 23
2018-09-23 00:00:00.000 162 354247 146
2018-09-23 00:00:00.000 159 382897 9
2018-09-23 00:00:00.000 94 570135 23
Essentially what I am wanting is the MAX quantity of each day with it's corresponding rate and bus_id.
For example, I would want the following rows from my sample data above:
ROOMDATE rate bus_id quantity
2018-09-21 00:00:00.000 159 382897 150
2018-09-22 00:00:00.000 159 382897 150
2018-09-23 00:00:00.000 162 354247 146

Answer 1

From what I have read, SQL Server 2000 did not support ROW_NUMBER. But we can phrase your query using a subquery which finds the max quantity for each day:
SELECT t1.*
FROM yourTable t1
INNER JOIN
(
SELECT
CONVERT(char(10), ROOMDATE, 120) AS ROOMDATE,
MAX(quantity) AS max_quantity
FROM yourTable
GROUP BY CONVERT(char(10), ROOMDATE, 120)
) t2
ON CONVERT(char(10), t1.ROOMDATE, 120) = t2.ROOMDATE AND
t1.quantity = t2.max_quantity
ORDER BY
t1.ROOMDATE;
Demo