WIDTH_BUCKET

WIDTH_BUCKET

Syntax width_bucket::=

WIDTH_BUCKET ( expr , min_value , max_value , num_buckets )

Purpose

WIDTH_BUCKET lets you construct equiwidth histograms, in which the histogram range is divided into intervals that have identical size. (Compare this function with NTILE, which creates equiheight histograms.) Ideally each bucket is a "closed-open" interval of the real number line. For example, a bucket can be assigned to scores between 10.00 and 19.999... to indicate that 10 is included in the interval and 20 is excluded. This is sometimes denoted [10, 20).

For a given expression, WIDTH_BUCKET returns the bucket number into which the value of this expression would fall after being evaluated.

■expr is the expression for which the histogram is being created. This expression must evaluate to a number or a datetime value. If expr evaluates to null, then the expression returns null.

■min_value and max_value are expressions that resolve to the end points of the acceptable range for expr. Both of these expressions must also evaluate to number or datetime values, and neither can evaluate to null.

■num_buckets is an expression that resolves to a constant indicating the number of buckets. This expression must evaluate to a positive integer.

Oracle also creates (when needed) an underflow bucket numbered 0 and an overflow bucket numbered num_buckets+1. These buckets handle values less than min_value and more than max_value and are helpful in checking the reasonableness of endpoints.

6-208 Oracle9i SQL Reference

WIDTH_BUCKET

Examples

The following example creates a ten-bucket histogram on the credit_limit column for customers in Switzerland in the sample table oe.customers and returns the bucket number ("Credit Group") for each customer. Customers with credit limits greater than the maximum value are assigned to the overflow bucket, 11:

SELECT customer_id, cust_last_name, credit_limit, WIDTH_BUCKET(credit_limit, 100, 5000, 10) "Credit Group" FROM customers WHERE nls_territory = ’SWITZERLAND’ ORDER BY "Credit Group";

Functions 6-209

XMLAGG

XMLAGG

Syntax

XMLAgg::=

Purpose

XMLAgg is an aggregate function. It takes a collection of XML fragments and returns an aggregated XML document. Any arguments that return null are dropped from the result.

XMLAgg is similar to SYS_XMLAgg except that XMLAgg returns a collection of nodes, but it does not accept formatting using the XMLFormat object. Also, XMLAgg does not enclose the output in an element tag as does SYS_XMLAgg.

Note: Within the order_by_clause, Oracle does not interpret number literals as column positions, as it does in other uses of this clause, but simply as number literals.

See Also: XMLELEMENT on page 6-214 and SYS_XMLAGG on page 6-165

Examples

The following example produces a Department element containing Employee elements with employee job ID and last name as the contents of the elements:

SELECT XMLELEMENT("Department", XMLAGG(XMLELEMENT("Employee", e.job_id||’ ’||e.last_name)

ORDER BY last_name)) as "Dept_list"

FROM employees e

WHERE e.department_id = 30;

Dept_list

-------------------------------------------------------------

<Department>

<Employee>PU_CLERK Baida</Employee>

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XMLAGG

<Employee>PU_CLERK Colmenares</Employee> <Employee>PU_CLERK Himuro</Employee> <Employee>PU_CLERK Khoo</Employee> <Employee>PU_MAN Raphaely</Employee> <Employee>PU_CLERK Tobias</Employee>

</Department>

The result is a single row, because XMLAgg aggregates the rows. You can use the GROUP BY clause to group the returned set of rows into multiple groups:

SELECT XMLELEMENT("Department",

XMLAGG(XMLELEMENT("Employee", e.job_id||’ ’||e.last_name))) AS "Dept_list"

FROM employees e

GROUP BY e.department_id;

Dept_list

---------------------------------------------------------

<Department>

<Employee>AD_ASST Whalen</Employee> </Department>

<Department>

<Employee>MK_MAN Hartstein</Employee> <Employee>MK_REP Fay</Employee>

</Department>

<Department>

<Employee>PU_MAN Raphaely</Employee> <Employee>PU_CLERK Khoo</Employee> <Employee>PU_CLERK Tobias</Employee> <Employee>PU_CLERK Baida</Employee> <Employee>PU_CLERK Colmenares</Employee> <Employee>PU_CLERK Himuro</Employee>

</Department>

...

Functions 6-211