Oracle PIVOT

Summary: in this tutorial, you will learn how to use the Oracle PIVOT clause to transpose rows to columns to generate result sets in crosstab format.

Introduction to Oracle PIVOT clause #

Oracle 11g introduced the new PIVOT clause that allows you to write cross-tabulation queries which transpose rows into columns, aggregating data in the process of the transposing. As a result, the output of a pivot operation returns more columns and fewer rows than the starting data set.

The following illustrates the basic syntax of the Oracle PIVOT clause:

SELECT 
    select_list
FROM 
    table_name
PIVOT [XML] ( 
    pivot_clause
    pivot_for_clause
    pivot_in_clause 
);
Code language: SQL (Structured Query Language) (sql)

In this syntax, following the PIVOT keyword are three clauses:

• pivot_clause specifies the column(s) that you want to aggregate. The pivot_clause performs an implicitly GROUP BY based on all columns that are not specified in the clause, along with values provided by the pivot_in_clause.
• pivot_for_clause specifies the column that you want to group or pivot.
• pivot_in_clause defines a filter for column(s) in the pivot_for_clause. The aggregation for each value in the pivot_in_clause will be rotated into a separate column.

Oracle PIVOT example #

Let’s create a new view named order_stats that includes product category, order status, and order id for demonstration.

CREATE VIEW order_stats AS
SELECT 
    category_name, 
    status, 
    order_id
FROM 
    order_items
INNER JOIN orders USING (order_id)
INNER JOIN products USING (product_id)
INNER JOIN product_categories USING (category_id);
Code language: SQL (Structured Query Language) (sql)

Here is the partial data from the order_stats view:

SELECT * FROM order_stats;Code language: SQL (Structured Query Language) (sql)

This example uses the PIVOT clause to return the number of orders for each product category by order status:

SELECT * FROM order_stats
PIVOT(
    COUNT(order_id) 
    FOR category_name
    IN ( 
        'CPU',
        'Video Card',
        'Mother Board',
        'Storage'
    )
)
ORDER BY status;
Code language: SQL (Structured Query Language) (sql)

In this example:

• The COUNT(order_id) is the pivot_clause.
• FOR category_name is the pivot_for_clause.

And here is the pivot_in_clause:

IN (
    'CPU',
    'Video Card',
    'Mother Board',
    'Storage'
)
Code language: SQL (Structured Query Language) (sql)

The COUNT() function returns the number of orders by category and order status. The query uses the values specified in the pivot_in_clause for the column headings of the result set.

Here is the output:

Aliasing pivot columns #

In the previous example, Oracle used product categories to generate pivot column names. On the other hand, you can alias one or more columns in the pivot_clause and one or more values in the pivot_in_clause.

Generally, Oracle uses the following convention to name the pivot columns based on aliases:

The following statement uses the query example above with the aliases:

SELECT * FROM order_stats
PIVOT(
    COUNT(order_id) order_count
    FOR category_name
    IN ( 
        'CPU' CPU,
        'Video Card' VideoCard, 
        'Mother Board' MotherBoard,
        'Storage' Storage
    )
)
ORDER BY status;
Code language: SQL (Structured Query Language) (sql)

Here is the result set:

As you can see, the pivot column names follow the below naming convention:

pivot_in_clause alias || '_' || pivot_clause aliasCode language: SQL (Structured Query Language) (sql)

Note that if you use more than one aggregate function in the pivot_clause, you must provide aliases for at least one of the aggregate functions.

Pivoting multiple columns #

In the previous example, you have seen that we used one aggregate function in the pivot_clause. In the following example, we will use two aggregate functions.

First, alter the order_stats view to include the order value column:

CREATE OR REPLACE VIEW order_stats AS
SELECT 
    category_name, 
    status, 
    order_id, 
    SUM(quantity * list_price) AS order_value
FROM 
    order_items
INNER JOIN orders USING (order_id)
INNER JOIN products USING (product_id)
INNER JOIN product_categories USING (category_id)
GROUP BY 
    order_id, 
    status, 
    category_name;
Code language: SQL (Structured Query Language) (sql)

Second, query data from the new order_stats view:

SELECT * FROM order_stats;
Code language: SQL (Structured Query Language) (sql)

Third, use PIVOT clause to return the number of orders and order values by product category and order status:

SELECT * FROM order_stats
PIVOT(
    COUNT(order_id) orders,
    SUM(order_value) sales
    FOR category_name
    IN ( 
        'CPU' CPU,
        'Video Card' VideoCard, 
        'Mother Board' MotherBoard,
        'Storage' Storage
    )
)
ORDER BY status;
Code language: SQL (Structured Query Language) (sql)

Here is the output:

As you can see from the output, the number of pivot columns is doubled, combining category_name with orders and sales.

Finally, use status as the pivot columns and category_name as rows:

SELECT * FROM order_stats
PIVOT(
    COUNT(order_id) orders,
    SUM(order_value) sales
    FOR status
    IN ( 
        'Canceled' Canceled,
        'Pending' Pending, 
        'Shipped' Shipped
    )
)
ORDER BY category_name;   
Code language: SQL (Structured Query Language) (sql)

The following picture shows the output:

Oracle PIVOT with subquery #

You cannot use a subquery in the pivot_in_clause. The following statement is invalid and causes an error:

SELECT * FROM order_stats
PIVOT(
    COUNT(order_id) orders,
    SUM(order_value) sales
    FOR category_name
    IN ( 
       SELECT category_name 
       FROM product_categories
    )
)
ORDER BY status;
Code language: SQL (Structured Query Language) (sql)

Here is the error message:

ORA-00936: missing expressionCode language: SQL (Structured Query Language) (sql)

This restriction is relaxed with the XML option:

SELECT * FROM order_stats
PIVOT XML (
    COUNT(order_id) orders,
    SUM(order_value) sales
    FOR category_name
    IN ( 
       SELECT category_name 
       FROM product_categories
    )
)
ORDER BY status;    
Code language: SQL (Structured Query Language) (sql)

This picture is the output:

Here is the sample of one PivotSet:

<PivotSet>
    <item>
        <column name="CATEGORY_NAME">CPU</column>
        <column name="ORDERS">13</column>
        <column name="SALES">4122040.7</column>
    </item>
    <item>
        <column name="CATEGORY_NAME">Mother Board</column>
        <column name="ORDERS">12</column>
        <column name="SALES">679121.39</column>
    </item>
    <item>
        <column name="CATEGORY_NAME">RAM</column>
        <column name="ORDERS">0</column>
        <column name="SALES" />
    </item>
    <item>
        <column name="CATEGORY_NAME">Storage</column>
        <column name="ORDERS">14</column>
        <column name="SALES">3023747.6</column>
    </item>
    <item>
        <column name="CATEGORY_NAME">Video Card</column>
        <column name="ORDERS">9</column>
        <column name="SALES">1677597.4</column>
    </item>
</PivotSet>Code language: HTML, XML (xml)

To view XML in the output grid from the SQL Developer, you follow these steps to set it up:

1)  From the Tool menu, select Preferences

2) Under Database > Advanced, check the option Display XML Value in Grid

The XML output format is not the same as the non-XML pivot one. For each value specified in the pivot_in_clause, the subquery returns a single XML string column.

The XML string for each row contains aggregated data corresponding to the implicit GROUP BY value of that row e.g., the number of orders ( ORDERS) and total sales ( SALES).

When you use a subquery in the pivot_in_clause, Oracle uses all values returned by the subquery for pivoting.

Note that the subquery must return a list of unique values. Otherwise, Oracle will raise a run-time error. If you are not sure whether the subquery returns a list of distinct values or not, you can use the DISTINCT keyword in the subquery.

Summary #

• Use the Oracle PIVOT clause to transpose rows to columns to make crosstab reports.

Quiz #