Replace SCATTER BY 1 with column name

[xuebinsu]

In Table-Value Expressions, SCATTER BY 1 will redistribute the data by constant number 1 instead of the first column. However, the example in the doc implies that SCATTER BY 1 will set the distribution key to the first column, which is not true.

This patch fixes this by changing the SCATTER BY 1 to SCATTER BY <column_name> in the example of the doc to show how to redistribute data by a column.

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• [ ] Add tests for the change
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