You said you tried to change from a str to a date - what did you do - did you try just recasting it as a date/time?
Please attach your twbx workbook so we can better understand what is going on
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when i did that the data disappear
Please post your book and I will look at it
It sounds like you are getting a NULL because you are simply reformatting data or trying to change the data type. I changed the data type on the string Market field and had the same result:
Instead, try to use date function DATEPARSE(<insert your string field>) or type conversion function DATE(<insert your string field>). This should work because it will parse (or convert) your string data into date data.
Let me know if this works. If it does, please mark the question as Answered.
If not, attach a workbook and we can investigate further.