Page 103 - CITS - Computer Software Application -TT

COMPUTER SOFTWARE APPLICATION - CITS

Example: COUNT()
SELECT COUNT(*)
FROM PRODUCT_GOOD;
Output:
10

Example: COUNT with WHERE
SELECT COUNT(*)
FROM PRODUCT_GOOD;
WHERE RATE>=200;
Output:

7
Example: COUNT() with DISTINCT
SELECT COUNT(DISTINCT COMPANY)
FROM PRODUCT_GOOD;
Output:

3
Example: COUNT() with GROUP BY
SELECT COMPANY, COUNT(*)
FROM PRODUCT_GOOD

Output:
ComA 5
ComB 3
ComC 2
Example: COUNT() with HAVING
SELECT COMPANY, COUNT(*)

SELECT COMPANY, COUNT(*)
GRHAV2;
Output:
ComA 5

ComB 3
Indexing and Query Optimization

Absolutely, your analogy of indexing to the index in a book is quite apt. It provides a clear and intuitive understanding
of how indexing works in databases.

In the context of databases, creating an index is akin to building a reference point for the data. Much like flipping
through a book’s index to quickly locate information, a database index allows for the rapid retrieval of specific
data without scanning through the entire dataset. This indexing technique significantly enhances the speed
and efficiency of queries, as the database can swiftly pinpoint the relevant information, leading to faster query
performance.
The intricacies of how databases achieve this efficiency through indexing can be explored further in the upcoming
sections of your article.

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CITS : IT&ITES - Computer software application - Lesson 18 - 36