MarcelBeug's avatar
MarcelBeug
Icon for Community Champion rankCommunity Champion
9 years ago
Status:
Done

Table.AddColumn and Table.DuplicateColumn may display invalid data (types) that can not be loaded

Issue moved from the old issue site (and slightly refined)   If you supply a columnType with Table.AddColumn or Table.DuplicateColumn (e.g. Byte.Type), then the Query Editor will also display value...
Data Modeling
v-haibl-msft's avatar
v-haibl-msft
Icon for Microsoft Employee rankMicrosoft Employee
9 years ago

MarcelBeug

 

I’ve got response from the team.

 

This is by design; see the language specification at http://download.microsoft.com/download/8/1/A/81A62C9B-04D5-4B6D-B162-D28E4D848552/Power%20Query%20Formula%20Language%20Specification%20(August%202015).pdf for the gory details.

 

Basically, the types of table columns are advisory. That means, it's not a contract which promises the values will actually have that type; it's just a marker which says you think the values should have that type. When you supply a type parameter to Table.AddColumn, you're asserting that you think the value will have that type but nothing enforces it. If you need the enforcement, you can either use "Byte.From" in your formula or you can add a subsequent transformation step to type "byte".

 

Best Regards,

Herbert

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