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Why group functions are not allowed in WHERE clause?
The reason, as I explained, is that this would require circular reasoning, because max and avg are not applied to all the rows in the base table; they are applied only to the rows that satisfy the where conditions! If you need max or avg for the entire base table, you must compute that separately in a subquery.
Can we use group function in WHERE clause?
Group functions cannot be used in WHERE clause. The can appear in SELECT, HAVING and ORDER BY clause.
Can we use WHERE clause in aggregate functions?
An aggregate function can be used in a WHERE clause only if that clause is part of a subquery of a HAVING clause and the column name specified in the expression is a correlated reference to a group. If the expression includes more than one column name, each column name must be a correlated reference to the same group.
When to use a function in an oracle query?
They are commonly used with the GROUP BY clause in a SELECT statement, where Oracle Database divides the rows of a queried table or view into groups. In a query containing a GROUP BY clause, the elements of the select list can be aggregate functions, GROUP BY expressions, constants, or expressions involving one of these.
When to use aggregate function in Oracle Database?
Aggregate Functions. Aggregate functions return a single result row based on groups of rows, rather than on single rows. Aggregate functions can appear in select lists and in ORDER BY and HAVING clauses. They are commonly used with the GROUP BY clause in a SELECT statement, where Oracle Database divides the rows of a queried table or view…
When to use aggregate functions in the HAVING clause?
You use aggregate functions in the HAVING clause to eliminate groups from the output based on the results of the aggregate functions, rather than on the values of the individual rows of the queried table or view.
Why is the where clause applied to each row?
“Conditions” are formally known as predicates and some predicates are used – by the query execution engine – to decide which rows are read from the base tables. These are called access predicates.) As you can see, the WHERE clause is applied to each row as it is presented to the engine.