sql - Reduce database records -

i have following table:

groupid startdate           time 1       2013-01-01 15:00    10 1       2013-01-01 16:00    10 1       2013-01-01 17:00    10 1       2013-01-02 08:00    10 1       2013-01-02 09:00    10 2       2013-01-01 15:00    2 2       2013-01-01 16:00    2 

which has record every hour in above example (in real data record every minute).

i need have such format today , yesterday, after time starts redundant - day grouping more enough.

i ways thinking following way of reducing above records:

1. run procedure every day copy data new "temp" table, grouping them together. drop original table , rename "temp" one. of course have restore relations (groupid column in above example).
2. have 2 tables time, , query view instead of table (i insert , select records). every day copy grouped records "grouped" table , remove them "detailed" table

in opinion both options generate problems, maybe there exist better way?

update

because of first answer think might misunderstood. result records should following

groupid startdate           time 1       2013-01-01 00:00    30 1       2013-01-02 00:00    20 2       2013-01-01 00:00    4 

so 1 record per day , group, , time column sum every detailed record.

instead of creating additional tables, can add additional rowid column table(auto generated id), , group unique columns, , use following query:

delete table1  table1 left outer join ( select min(rowid) rowid, groupid, startdate, time  table1  group groupid, startdate, time ) table2 on table1.rowid = table2.rowid table2.rowid null 

here explanation: have table following data:

 groupid    startdate    time    rowid  1  2013-01-01 15:01:00.000 10  101  1  2013-01-01 15:09:00.000 10  102  1  2013-01-01 15:59:00.000 10  103  1  2013-01-01 16:42:00.000 10  104  1  2013-01-01 16:52:00.000 10  105  1  2013-01-01 17:21:00.000 10  106  1  2013-01-01 17:46:00.000 10  107  1  2013-01-01 17:56:00.000 10  108  1  2013-01-02 08:10:00.000 10  109  1  2013-01-02 09:20:00.000 10  110  2  2013-01-01 15:45:00.000 2   111  2  2013-01-01 15:35:00.000 2   112  2  2013-01-01 16:35:00.000 2   113 

now after run following query left 1 row per day:

delete table1  test24 table1 left outer join ( select min(rowid) rowid, groupid, convert(varchar(10),startdate,120)startdate, time  test24  group groupid, convert(varchar(10),startdate,120), time ) table2 on table1.rowid = table2.rowid table2.rowid null   groupid    startdate           time    rowid    1    2013-01-01 15:01:00.000 10  101    1    2013-01-02 08:10:00.000 10  109    2    2013-01-01 15:45:00.000 2   111 

now, can run update statement change date per required format.

update test24 set startdate=convert(varchar(10),startdate,120)  groupid startdate     time    rowid    1    2013-01-01       10   101    1    2013-01-02       10   109    2    2013-01-01        2   111