SQL-DATA ANALYSIS,AN INTRODUCTION
Tags: beginners, datascience, sql, codenewbie
Published: 2023-02-18 15:51:11

## **HISTORY OF SQL**
Dr Edgar F. “Ted” Codd is known as the _father of relational databases_ as he described a relational model for databases in his paper, “_A Relational Model of Data for Large Shared Data Banks_,” in 1970.IBM researchers Donald Chamberlin and Raymond Boyce, in 1970 developed **SQL(Structured Query Language**) and it was created to help manage the existing IBM system R database. In the following years after its development, SQL gained popularity with other companies such as Oracle and Microsoft. Oracle also commercially released its own version of SQL called oracle V2.
Later on,American National Standards Institute (ANSI) and the International Organization for Standardization made SQL the standard language in relational database communication. Today,SQL is very popular for managing data and has greatly improved the development of data driven decision in businesses.

## **TYPES OF DATABASES**
SQL operates databases; it includes Database Creation,Deletion, Fetching Data Rows, Modifying & Deleting Data rows, etc.
Different databases include:
**1.Relational databases**: Relational databases store data in tables.Each table contains rows (records) and columns (fields). The relationship between tables is established using keys, which can be used to join tables and retrieve data. Relational databases are widely used in business applications.Popular examples include _MySQL, Oracle, and Microsoft SQL Server._
**2.NoSQL databases:** NoSQL databases store data in flexible, semi-structured formats such as JSON or XML. NoSQL databases are designed to handle large volumes of unstructured data and are commonly used in web applications and big data processing. Popular examples of NoSQL databases include _MongoDB, Cassandra, and Redis_.
**3.Object-oriented databases:** Object-oriented databases store data in the form of objects, which can include both data and behavior. They are designed to support complex data models and are commonly used in applications that involve complex data relationships, such as CAD systems or scientific simulations. Popular examples of object-oriented databases include _db4o and ObjectStore._
**4.Hierarchical databases:**Hierarchical databases organize data in a tree-like structure, with parent-child relationships between data elements. These databases are primarily used in mainframe environments and are suited to handling simple data structures with high transaction volumes. Examples of hierarchical databases include _IBM's Information Management System (IMS) and Windows Registry_.
**5.Graph databases:**Graph databases store data as nodes and edges.Nodes represent entities and edges represent relationships between them. These databases are designed to handle complex relationships between data elements and are commonly used in applications that require sophisticated data modeling, such as social networks or recommendation systems. Popular examples of graph databases include _Neo4j, ArangoDB, and OrientDB_.

## **HOW SQL RELATES TO DATA ANALYSIS**
SQL relates to the data analysis process through
**1.Data preparation**:This typically involves cleaning and transforming the data to ensure that it is in a suitable format for analysis. SQL can be used to perform these tasks, such as filtering out irrelevant data, merging or joining data from multiple tables, and aggregating data to generate summary statistics.
**2.Data exploration:**  SQL can be used to query the data and generate reports and visualizations that help to identify key insights. This involves using SQL functions to calculate summary statistics, or using subqueries to filter and analyze specific subsets of the data.
**3.Data modeling:** SQL can be used to build models by using advanced analytical functions and algorithms, such as regression analysis or clustering.
**4.Data visualization:** SQL can be used to generate reports and visualizations that can be shared with stakeholders, such as graphs, charts, and dashboards.
SQL is a critical component of the data analysis process, as it provides a powerful and flexible tool for querying, manipulating, and analyzing data. By using SQL, data analysts can quickly and easily access and explore large data sets, and generate insights that can inform decision-making and drive business outcomes.

## **Basic SQL queries:**
The most common SQL query used in data analysis is the **SELECT statement**. This statement _retrieves data from a table and returns the specified columns_. 
For example, the following SELECT statement would return all columns from the table 'employees':

```
SELECT * FROM employees; 
```
Another common query is filtering data using **WHERE clauses**. The WHERE clause is _used to filter data based on a specified condition._
For example, the following query would return all employees          with a salary greater than $50,000:

```
SELECT * FROM employees WHERE salary > 50000; 
```
Sorting data using **ORDER BY clauses** is also a common SQL query. This clause is _used to sort the data in ascending or descending order based on a specified column_. 
For example, the following query would return all employees sorted by salary in descending order:

```
SELECT* FROM employees ORDER BY salary DESC; 
```

Grouping data using **GROUP BY clauses** is _used to group data based on one or more columns_. This is often used in combination with aggregate functions to calculate statistics for each group. For example, the following query would return the total salary for each department:

```
SELECT department, SUM(salary) FROM employees GROUP BY department;
```
**Joins:**
Joins are _essential for combining data from multiple tables in SQL_. There are different types of joins, including _inner joins, outer joins, and cross joins_. Inner joins _return only the rows that have matching values in both tables_, while outer joins _return all rows from one table and matching rows from the other table_. **Cross joins** _return the Cartesian product of two tables_, meaning all possible combinations of rows.
For example, the following query would return all orders and their corresponding customers:

```
SELECT orders.order_id, customers.customer_name FROM orders INNER JOIN customers ON orders.customer_id = customers.customer_id; 
```

**Subqueries:**
Subqueries are another important tool in SQL data analysis, _allowing you to nest one query inside another to perform more complex analysis_. A subquery can be used to _filter, aggregate, or perform calculations on data_, and can be used in a variety of SQL statements, including SELECT, INSERT, UPDATE, and DELETE.
For example, the following query would return all employees with a salary greater than the average salary:

```
SELECT * FROM employees WHERE salary > (SELECT AVG(salary) FROM employees);
```
**Data aggregation and grouping:**
SQL offers several functions for data aggregation and grouping, such as **COUNT, SUM, AVG, and MAX**. These functions allow you to perform operations on sets of data, either across an entire table or within groups of data defined by the GROUP BY clause. Data aggregation and grouping are often used to calculate statistics, identify patterns and trends, and create reports. 
For example, the following query would return the number of employees in each department:


```
SELECT department, COUNT(*) FROM employees GROUP BY department;
```
**Advanced SQL topics:**
Once you have covered the basics of SQL data analysis, you can move on to more advanced topics. Window functions, for example, allow you to perform calculations across a set of rows that are related to the current row. Common table expressions can simplify complex queries by allowing you to define subqueries as temporary tables, and stored procedures can automate repetitive tasks and reduce errors. Optimizing SQL queries is also important for improving query performance, and techniques such as indexing, normalizing data, and using query plans can help to achieve this. 

**Case Studies**
We will explore some real-world case studies to illustrate how SQL is used in different industries to gain insights into their data.
**1.Finance:** One of the most common use cases for SQL in finance is fraud detection. For example, a credit card company might use SQL to analyze transaction data and identify patterns that suggest fraudulent activity. By running queries to identify transactions that are outside of a customer's normal spending patterns or that match known patterns of fraud, the company can detect and prevent fraudulent activity in real time.
**2.Healthcare:** In healthcare, SQL is often used to analyze patient data and identify patterns that can help improve patient outcomes. For example, a hospital might use SQL to analyze patient records and identify risk factors for certain diseases or conditions. By identifying patients who are at high risk for certain conditions, the hospital can take proactive measures to prevent the onset of the disease or condition and improve patient outcomes.

In each of these case studies, SQL was used to analyze large datasets and extract valuable insights that helped these industries make more informed decisions. By leveraging the power of SQL, companies can gain a competitive advantage by making data-driven decisions that are based on real-time insights into their business operations

**In conclusion**, SQL is a powerful tool for data analysis that can be used across various industries. In this article, we covered the basics of SQL queries, including selecting data, filtering data, sorting data, and grouping data. We also explored more advanced topics such as joins, subqueries, data aggregation, and grouping. Lastly, we presented some case studies that showcased how SQL is used in real-world scenarios. If you are new to SQL data analysis, we recommend practicing these queries on sample data and seeking additional resources such as books, online courses, or community forums to further your skills. With SQL, you can unlock the potential of your data and gain valuable insights that can drive informed decisions.

Here are some sample resources for further learning on SQL data analysis:

**Books:**
       •"SQL for Data Analysis" by Brian Overland
       •"Learning SQL" by Alan Beaulieu
       •"Data Analytics Made Accessible" by Anil Maheshwari
**Online courses:**
       •SQL for Data Analysis - Udacity
       •SQL - Codecademy
       •Data Analysis with SQL - Coursera
**Community forums:**
       •Reddit - r/SQL
       •Stack Overflow
       •SQLServerCentral