# Best approach to map day of date in bulk

We need to map the Date field so that every date value is the first of the month. The value mapper tile can do this one at a time, but we need to do this in bulk. Can anyone recommend the best approach using a function?

• ````Date` - INTERVAL (DATOFMONTH(`Date`) - 1) DAY
```
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• I'm getting an 'unknown function:DATOFMONTH' error in my ETL preview on this @GrantSmith I tried `Date` - INTERVAL (DATEOFMONTH(`Date`) - 1) DAY in case there was a typo on DATE, but still get 'unknown function'

As a workaround I used Date Function to extract Month of Date and the function below

CASE

WHEN MONTH(`Date`) = 1 then '1/1/2022'

WHEN MONTH(`Date`) = 2 then '2/1/2022'

WHEN MONTH(`Date`) = 3 then '3/1/2022'

WHEN MONTH(`Date`) = 4 then '4/1/2022'

WHEN MONTH(`Date`) = 5 then '5/1/2022'

WHEN MONTH(`Date`) = 6 then '6/1/2022'

WHEN MONTH(`Date`) = 7 then '7/1/2022'

WHEN MONTH(`Date`) = 8 then '8/1/2022'

WHEN MONTH(`Date`) = 9 then '9/1/2022'

WHEN MONTH(`Date`) = 10 then '10/1/2022'

WHEN MONTH(`Date`) = 11 then '11/1/2022'

WHEN MONTH(`Date`) = 12 then '12/1/2022'

end

• Should be DAYOFMONTH