Convert Rowset variables to scalar value

2020-02-12 11:41发布

Is it possible to convert rowset variables to scalar value for eg.

@maxKnownId =
    SELECT MAX(Id) AS maxID
    FROM @PrevDayLog;

DECLARE @max int = @maxKnownId;

标签: u-sql
2条回答
虎瘦雄心在
2楼-- · 2020-02-12 12:12

Thanks for input, below is the business cases -

We have catalog data coming from source for which we need to generate unique ids. With ROW_NUMBER() OVER() AS Id method we can generate unique id. But while merging new records it changes ids of existing records also and causes issues with relational data

Below is simple solutions

//get max id from existing catalog

@maxId =
    SELECT (int)MAX(Id) AS lastId
    FROM @ExistingCat;

//because @maxId is not scalar, we will do CROSS JOIN so that maxId is repeated for every record.
//ROW_NUMBER() always starts from 1, we can generate next Id with maxId+ROW_NUMBER()

@newRecordsWithId =
    SELECT (int)lastId + (int)ROW_NUMBER() OVER() AS Id,
           CatalogItemName
    FROM @newRecords CROSS JOIN @maxId;
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冷血范
3楼-- · 2020-02-12 12:22

There is no implicit conversion of a single-cell rowset to a scalar value in U-SQL (yet).

What are you interested in using the value for?

Most of the time you can write your U-SQL expression in a way that you do not need the scalar variable. E.g., if you want to use the value in a condition in another query, you could just use the single value rowset in a join with the other query (and with the right statistics, I am pretty sure that the optimizer would turn it into a broadcast join).

If you feel you cannot easily write the expression without the rowset to a scalar, please let us know via http://aka.ms/adlfeedback by providing your scenario.

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