I have encountered a script like this: set @sum = sum = (case when somecol1 is null then DATEDIFF(d,[somecol2],somecol3) else 0 end) I can't understand the meaning of the equal sign (=) after the second keyword sum. When I run the query it is not showing any errors both with the equal sign and without. I want to know the purpose of putting an equal sign after the keyword `sum`. Is that a mistake or not?
This is documented in [UPDATE (Transact-SQL)]: > SET @variable = column = expression sets the variable to the same value as the column. This differs from SET @variable = column, column = expression, which sets the variable to the pre-update value of the column. In your code example, `sum` is the (unwise) name of a column, not an aggregate. Demo: <>https://dbfiddle.uk/?rdbms=sqlserver_2017&fiddle=8aa0603ba344816390cb287b842385de : https://docs.microsoft.com/en-us/sql/t-sql/queries/update-transact-sql : https://dbfiddle.uk/?rdbms=sqlserver_2017&fiddle=8aa0603ba344816390cb287b842385de