How to write a loop for such sql query

I need to write such query:

SELECT CAST (date_time_column AS DATE)  as 'Date',
 AVG(CASE WHEN FORMAT(date_time_column, 'HH:mm') = '00:00' then my_values ELSE NULL end) as '00:00',
 ........
 AVG(CASE WHEN FORMAT(date_time_column, 'HH:mm') = '23:59' then my_values ELSE NULL end) as '23:59'
 FROM table
 where date_time_column > '2021-08-12'
 GROUP BY CAST (date_time_column AS DATE)

What is a way to avoid writing 1440 lines in a query?

Answer

Try the below method (Change the variables to match your table and field)

/*Generate all minutes in a day in a string variable*/
Declare @timeRange varchar(max)=null
declare @startdate Datetime='2021-08-12 00:00';
; WITH cte AS
(
SELECT 1 i, @startdate AS resultDate
UNION ALL
SELECT i + 1, DATEADD(minute, i, @startdate )
FROM cte 
WHERE DATEADD(minute, i, @startdate ) < DateAdd(day,1,@startdate)
)

SELECT @timeRange=Coalesce(@timeRange +',' +  '['+Format(resultDate,'HH:mm')+']','['+Format(resultDate,'HH:mm')+']') FROM cte
OPTION (MAXRECURSION 2000);




/* (Change These variables to match your table & fields  */
declare @filterQuery varchar(300)=' where {date_time_column}>''2021-01-01''';
declare @dateTimeColumn varchar(30)='{date_time_column}';
declare @valueColumn varchar(30)='{value_column}';
declare @myTable  varchar(20)='{my_table}';


/*Generate Pivot Query */
DECLARE @query  AS NVARCHAR(MAX);

set @query= '
SELECT *
FROM (SELECT Cast('+ @dateTimeColumn +' as Date) Resultdate, 
       FORMAT(' + @dateTimeColumn + ', ''HH:mm'') DateMinute, 
       ' + @valueColumn + ' FROM ' + @myTable + ' ' + @filterQuery +'
     ) FormattedData
PIVOT( AVG('+ @valueColumn + ')   
    FOR DateMinute IN ('+ @timeRange +')
     ) AS pivotTable

';

/*Execute Generated Query*/

execute(@query)