#gate cs applied course

Question

how both query result is the same, please give an example.

Answer 1

It is not possible to determine the truth or falsehood of any statements about the queries Q1 and Q2 without additional information. These queries are written in a structured query language (SQL) that is used to retrieve and manipulate data from a database, but the exact meaning and implications of the queries depend on the structure and contents of the database R, as well as the specific implementation of SQL that is being used. For example, the queries might retrieve different sets of data from R if the database includes duplicate values of column a, or if the implementation of SQL treats the GROUP BY clause differently from the DISTINCT keyword.

Answer 2

It does not always result in same answer,

there are two cases first if a is unique and it has certain repeating values.

Now lets try to understa group by and select, If group by on non unique terms and apply select term returns first value from each group.

And if terms are unique it will return single term by using group by or not