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I am trying to extract the first not null value from a column of values based on timestamp. Can somebody share your thoughts on this. Thank you.
What have i tried so far?
FIRST_VALUE( column ) OVER ( PARTITION BY id ORDER BY timestamp)
Input :-
id,column,timestamp
1,NULL,10:30 am
1,NULL,10:31 am
1,'xyz',10:32 am
1,'def',10:33 am
2,NULL,11:30 am
2,'abc',11:31 am
Output(expected) :-
1,'xyz',10:30 am
1,'xyz',10:31 am
1,'xyz',10:32 am
1,'xyz',10:33 am
2,'abc',11:30 am
2,'abc',11:31 am
986
SQL COALESCE – a function that returns the first defined, i.e. non-NULL value from its argument list. Usually one or more COALESCE function arguments is the column of the table the query is addressed to. Often a subquery is also an argument for a function.
The syntax is as follows: Select * from table_source where column is not NULL; If you want to read more about the where operator, please refer to the documentation. In addition if you want to replace the null values, you can use the IFNNULL() function.
You can retrieve or exclude rows that contain a null value in a specific row. You can use a WHERE clause to retrieve rows that contain a null value in a specific column. You can also use a predicate to exclude null values. You cannot use the equal sign to retrieve rows that contain a null value.
You can modify your sql like this to get the data you want.
FIRST_VALUE( column )
OVER (
PARTITION BY id
ORDER BY
CASE WHEN column IS NULL then 0 ELSE 1 END DESC,
timestamp
)
Try this old trick of string manipulation:
Select
ID,
Column,
ttimestamp,
LTRIM(Right(CColumn,20)) as CColumn,
FROM
(SELECT
ID,
Column,
ttimestamp,
MIN(Concat(RPAD(IF(Column is null, '9999999999999999',STRING(ttimestamp)),20,'0'),LPAD(Column,20,' '))) OVER (Partition by ID) CColumn
FROM (
SELECT
*
FROM (Select 1 as ID, STRING(NULL) as Column, 0.4375 as ttimestamp),
(Select 1 as ID, STRING(NULL) as Column, 0.438194444444444 as ttimestamp),
(Select 1 as ID, 'xyz' as Column, 0.438888888888889 as ttimestamp),
(Select 1 as ID, 'def' as Column, 0.439583333333333 as ttimestamp),
(Select 2 as ID, STRING(NULL) as Column, 0.479166666666667 as ttimestamp),
(Select 2 as ID, 'abc' as Column, 0.479861111111111 as ttimestamp)
))
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