Question

1.Describe summary queries. (In 150 to 300 words)

Answer 1

Summary queries:

Summary queries (also called Group-By queries) are used to summarise the contents of a table.

Creating Summary Queries:

When we want to generate rows of data that summarize data in our tables. For example, we want to find a sum or an average for the values in a column. For doing this we  create a computed column that includes aggregate (column) functions.

If a computed column involving an aggregate function is added to a query, the system implicitly  defines a GROUP BY clause for us. We can also modify GROUP BY clause, or add a GROUP BY clause for a query , the Group command from the Query menu or the Group button on the toolbar.

To add a column to the GROUP BY clause, move it from the left list box to the right list box using the arrow buttons. To change the relative order of columns within the GROUP BY clause, use the Up and Down buttons.

Creating Summary Queries in SQL:

The GROUP BY statement groups rows that have the same values into summary rows.The GROUP BY statement is often used with aggregate functions (COUNT, MAX, MIN) to group the result-set by one or more columns.

SELECT COUNT(students),Students
FROM Class
GROUP BY Section;

This SQL  statement will group the students from each section in class thus giving us the idea that from class X there are four section with each section having Y number of students.

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