Query to print null if there are no data available for the selected date

Question

Suppose I have data available for 09-02-2020 and I want last 8 days data between 01-02-2020 to 09-02-2020 but if there is no data available for 01-02-2020 to 08-02-2020 so then just print " - " at the place of data.

I want the query for this scenario.

Expected Output -:

|Date          counts|
|09-02-2020       15 |
|08-02-2020        - |
|07-02-2020        - |
|06-02-2020        - |         
|05-02-2020        - |
|04-02-2020        - |
|03-02-2020        - |
|02-02-2020        - |
|01-02-2020        - |

Answer 1

Assuming that data is stored in Test table with date and value. Try below query:

select t1.selected_date,case when t2.val is null then "-" else convert(t2.val,char) end as val from 
(select selected_date from 
(select adddate('1970-01-01',t4.i*10000 + t3.i*1000 + t2.i*100 + t1.i*10 + t0.i) selected_date from
 (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t0,
 (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t1,
 (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t2,
 (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t3,
 (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t4) v
where selected_date between '2020-02-01' and '2020-02-09'
)
 t1
 left join test t2 on t1.selected_date=t2.date order by t1.selected_date desc;

Output:

2020-02-09  -
2020-02-08  -
2020-02-07  -
2020-02-06  -
2020-02-05  -
2020-02-04  1
2020-02-03  6
2020-02-02  5
2020-02-01  1

If the data type of date column is varchar then you can convert it using CONVERT(column_name as date) and above will use the date format as YYYY-MM-DD so you will have to change the date format using DATE_FORMAT .