Select value A, value B, or both [duplicate]

1. How do I query duplicate values in SQL?
2. Does count (*) include duplicate values?
3. Which keyword selects values excluding duplicate values?

How do I query duplicate values in SQL?

Using the GROUP BY and HAVING clauses we can show the duplicates in table data. The GROUP BY statement in SQL is used to arrange identical data into groups with the help of some functions. i.e if a particular column has the same values in different rows then it will arrange these rows in a group.

Does count (*) include duplicate values?

COUNT(*) with GROUP BY returns the number of rows in each group. This includes NULL values and duplicates. COUNT(ALL <expression>) evaluates expression for each row in a group, and returns the number of nonnull values.

Which keyword selects values excluding duplicate values?

The DISTINCT keyword in the SELECT clause is used to eliminate duplicate rows and display a unique list of values. In other words, the DISTINCT keyword retrieves unique values from a table.