Oracle 10g SQL Fundamentals II--Les04

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Generating Reports by GroupingRelated Data : 

Generating Reports by GroupingRelated Data

Objectives : 

Objectives After completing this lesson, you should be able to do the following: Use the ROLLUP operation to producesubtotal values Use the CUBE operation to produce cross-tabulation values Use the GROUPING function to identify the row values created by ROLLUP or CUBE Use GROUPING SETS to produce a single result set

Review of Group Functions : 

Review of Group Functions Group functions operate on sets of rows to give one result per group. Example: SELECT [column,] group_function(column). . . FROM table [WHERE condition] [GROUP BY group_by_expression] [ORDER BY column]; SELECT AVG(salary), STDDEV(salary), COUNT(commission_pct),MAX(hire_date) FROM employees WHERE job_id LIKE 'SA%';

Review of the GROUP BY Clause : 

Review of the GROUP BY Clause Syntax: Example: SELECT department_id, job_id, SUM(salary), COUNT(employee_id) FROM employees GROUP BY department_id, job_id ; SELECT [column,] FROM table [WHERE condition] [GROUP BY group_by_expression] [ORDER BY column]; group_function(column). . .

Review of the HAVING Clause : 

Review of the HAVING Clause Use the HAVING clause to specify which groups are to be displayed. You further restrict the groups on the basis of a limiting condition. SELECT [column,] group_function(column)... FROM table [WHERE condition] [GROUP BY group_by_expression] [HAVING having_expression] [ORDER BY column];

GROUP BY with ROLLUP andCUBE Operators : 

GROUP BY with ROLLUP andCUBE Operators Use ROLLUP or CUBE with GROUP BY to produce superaggregate rows by cross-referencing columns. ROLLUP grouping produces a result set containing the regular grouped rows and the subtotal values. CUBE grouping produces a result set containing the rows from ROLLUP and cross-tabulation rows.

ROLLUP Operator : 

ROLLUP Operator ROLLUP is an extension to the GROUP BY clause. Use the ROLLUP operation to produce cumulative aggregates, such as subtotals. SELECT [column,] group_function(column). . . FROM table [WHERE condition] [GROUP BY [ROLLUP] group_by_expression] [HAVING having_expression]; [ORDER BY column];

ROLLUP Operator: Example : 

ROLLUP Operator: Example 3 1 2

CUBE Operator : 

CUBE Operator CUBE is an extension to the GROUP BY clause. You can use the CUBE operator to produce cross-tabulation values with a single SELECT statement. SELECT [column,] group_function(column)... FROM table [WHERE condition] [GROUP BY [CUBE] group_by_expression] [HAVING having_expression] [ORDER BY column];

CUBE Operator: Example : 

CUBE Operator: Example SELECT department_id, job_id, SUM(salary) FROM employees WHERE department_id < 60 GROUP BY CUBE (department_id, job_id) ; 1 2 3 4

GROUPING Function : 

GROUPING Function The GROUPING function: Is used with either the CUBE or ROLLUP operator Is used to find the groups forming the subtotal in a row Is used to differentiate stored NULL values from NULL values created by ROLLUP or CUBE Returns 0 or 1

GROUPING Function: Example : 

GROUPING Function: Example SELECT department_id DEPTID, job_id JOB, SUM(salary), GROUPING(department_id) GRP_DEPT, GROUPING(job_id) GRP_JOB FROM employees WHERE department_id < 50 GROUP BY ROLLUP(department_id, job_id); 1 2 3

GROUPING SETS : 

GROUPING SETS GROUPING SETS syntax is used to define multiple groupings in the same query. All groupings specified in the GROUPING SETS clause are computed and the results of individual groupings are combined with a UNION ALL operation. Grouping set efficiency: Only one pass over the base table is required. There is no need to write complex UNION statements. The more elements GROUPING SETS has, the greater the performance benefit.

Notes Only : 

Notes Only

GROUPING SETS: Example : 

GROUPING SETS: Example SELECT department_id, job_id, manager_id,avg(salary) FROM employees GROUP BY GROUPING SETS ((department_id,job_id), (job_id,manager_id)); … 1 … 2

Notes Only : 

Notes Only

Composite Columns : 

Composite Columns A composite column is a collection of columns that are treated as a unit. ROLLUP (a, , d) Use parentheses within the GROUP BY clause to group columns, so that they are treated as a unit while computing ROLLUP or CUBE operations. When used with ROLLUP or CUBE, composite columns would require skipping aggregation across certain levels. (b,c)

Notes Only : 

Notes Only

Composite Columns: Example : 

Composite Columns: Example SELECT department_id, job_id, manager_id, SUM(salary) FROM employees GROUP BY ROLLUP( department_id,(job_id, manager_id)); … 2 1

Concatenated Groupings : 

Concatenated Groupings Concatenated groupings offer a concise way to generate useful combinations of groupings. To specify concatenated grouping sets, you separate multiple grouping sets, ROLLUP, and CUBE operations with commas so that the Oracle server combines them into a single GROUP BY clause. The result is a cross-product of groupings from each grouping set.

Concatenated Groupings: Example : 

… … … Concatenated Groupings: Example SELECT department_id, job_id, manager_id, SUM(salary) FROM employeesGROUP BY department_id, ROLLUP(job_id), CUBE(manager_id);

Summary : 

Summary In this lesson, you should have learned how to use the: ROLLUP operation to produce subtotal values CUBE operation to produce cross-tabulation values GROUPING function to identify the row values created by ROLLUP or CUBE GROUPING SETS syntax to define multiple groupings in the same query GROUP BY clause to combine expressions in various ways: Composite columns Concatenated grouping sets

Practice 4: Overview : 

Practice 4: Overview This practice covers using: ROLLUP operators CUBE operators GROUPING functions GROUPING SETS

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