What does select distinct do in the in subquery?

What does select distinct do in the in subquery?

The SELECT DISTINCT in the IN subquery does nothing. Nothing at all. The IN implicitly does a SELECT DISTINCT because if something is in (1, 2, 3), then that something is in (1, 1, 1, 2, 2, 3). What you want to do is to count the number of times that idProdotto appears in the table.

Can you select distinct fields but return all columns?

Something like: On most platforms, however, neither of the above will work because the behavior on the other columns is unspecified. (The first works in MySQL, if that’s what you’re using.) You could fetch the distinct fields and stick to picking a single arbitrary row each time.

Do you need to Rewrite Your subquery query?

Cheers. You need to rewrite you query. as you can only have one select column in your inner select statement. Use the Cross Apply or Outer Apply instead You need to rewrite you query. as you can only have one select column in your inner select statement. Use the Cross Apply or Outer Apply instead

When to select distinct field1, field2, field3?

SELECT DISTINCT FIELD1, FIELD2, FIELD3 FROM TABLE1 works if the values of all three columns are unique in the table. If, for example, you have multiple identical values for first name, but the last name and other information in the selected columns is different, the record will be included in the result set.

What can hints be used for in SQL?

You can use hints to specify the following: The optimization approach for a SQL statement. The goal of the cost-based optimizer for a SQL statement. The access path for a table accessed by the statement. The join order for a join statement.

What’s the difference between a subquery and an inner query?

A subquery is also called an inner query or inner select, while the statement containing a subquery is also called an outer query or outer select. Many Transact-SQL statements that include subqueries can be alternatively formulated as joins.

What to do with a subquery introduced with exists?

The select list of a subquery introduced with EXISTS, by convention, has an asterisk (*) instead of a single column name. The rules for a subquery introduced with EXISTS are the same as those for a standard select list, because a subquery introduced with EXISTS creates an existence test and returns TRUE or FALSE, instead of data.

When to use exists, distinct, and unique in SQL?

Although the EXISTS predicate evaluates to True only if the subquery returns at least one row, the UNIQUE predicate evaluates to True only if no two rows returned by the subquery are identical. In other words, the UNIQUE predicate evaluates to True only if all the rows that its subquery returns are unique.

How to SELECT DISTINCT values in a table?

Sometimes, you may want to get only distinct values in a specified column of a table. To do this, you use the SELECT DISTINCT clause as follows: SELECT DISTINCT column_name FROM table_name; Code language: SQL (Structured Query Language) (sql)

When to use the SELECT DISTINCT clause in SQL Server?

Introduction to SQL Server SELECT DISTINCT clause. Sometimes, you may want to get only distinct values in a specified column of a table. To do this, you use the SELECT DISTINCT clause as follows: The query returns only distinct values in the specified column. In other words, it removes the duplicate values in the column from the result set.