SQL solves the uniqueness of distinct and groupby statements

Test environment: mssql2005

Sometimes we need to select a column as a unique value. The methods include distinct and groupby. However, if we select multiple columns, the results may not be unique if it is a non-aggregate function.

 

Therefore, using virtual columns makes sense.

 

Examples of online borrowing:

How to select a virtual column and fill it with null? Suppose there is only one column in the table, tselect distinct T, 0 as C1, 'abc' as C2, ''as C3 from table the result is t C1 C2 C31 0 ABC 2 0 abc3 0 ABC so that we can obtain the unique value of T, and also obtain the column C1, C2, c3 in disguise to solve some Application Problems of distinct and groupby.