如何使用特定的日期格式简化和减少我的SQL查询的执行时间？

Question

I am using jdbcTemplate with following query and code

    String sql = select count(*) as count ,trunc(fin.fin_date) as dateAndTime from  (select * from rec where rec_status='RECEIVED' and fin_date>sysdate-8) fin group by trunc(fin.fin_date)

    try {
        return jdbcTemplate.query(sql, new RowMapper<Chrt>() {
            @Override
            public Chrt mapRow(ResultSet rs, int rowNum) throws SQLException {
                Chrt receive = new Chrt();
                java.util.Date date =(rs.getDate("dateAndTime"));
                receive.setDate(date.toString());
                receive.setCount(rs.getInt("count"));
                return receive;
            }
        });
    } catch (DataAccessException e) {
        return null;
    }
 }

It returns me date in a format like 2016-05-19 but I need the date like 19-MAY-16. Is it possible to get this format without increasing execution time?

How can I do this?

Answer 1

Instead of the trunc function, you can use the TO_CHAR function. It will give you the date in the specified format:

String sql = select count(*) as count ,TO_CHAR(fin.fin_date, 'DD-MON-YY') as dateAndTime from  (select * from rec where rec_status='RECEIVED' and fin_date>sysdate-8) fin group by TO_CHAR(fin.fin_date, 'DD-MON-YY');

This will not impact performances significantly.

---

To increase performances, I suggest you to look at the query plan for the query. To see this plan, just execute :

EXPLAIN PLAN FOR 
select count(*) as count ,TO_CHAR(fin.fin_date, 'DD-MON-YY') as dateAndTime from  (select * from rec where rec_status='RECEIVED' and fin_date>sysdate-8) fin group by TO_CHAR(fin.fin_date, 'DD-MON-YY')

in any oracle sql client and read the doc to understand why it is too slow and how to improve performances. (a blind guess : put an index on fin_date)

Answer 2

Why not use one query instead of two ?

select count(*) as count ,TO_CHAR(fin.fin_date, 'DD-MON-YY') as dateAndTime 
from rec 
where rec_status='RECEIVED' and fin_date>sysdate-8
group by TO_CHAR(fin.fin_date, 'DD-MON-YY');