Ramya .C

Posted on Aug 16, 2025

Day 17 of My Data Analytics Journey !

Learning SQL Data Types & Operators

Today marks Day 17 of my Data Analytics learning journey, and I explored one of the most important topics in SQL – Data Types and Operators. These are the foundation for writing queries correctly and performing meaningful operations on data.

To practice, I also created a Hospital database using different data types and applied SQL operators to perform calculations and comparisons.

🔹 SQL Data Types

In SQL, every column in a table must have a data type. Data types tell the database what kind of values can be stored in a column (numbers, text, dates, etc.).

Here are the main categories of SQL data types:

1. Numeric Data Types

INT → Whole numbers (e.g., 10, -5, 1000)
DECIMAL(p,s) → Fixed precision decimal values (e.g., 123.45)
FLOAT / REAL → Approximate decimal values (e.g., 3.14159)

👉 Used when storing things like age, salary, or percentage.

2. Character/String Data Types

CHAR(n) → Fixed-length string (e.g., 'RAMYA ' with length 5)
VARCHAR(n) → Variable-length string (saves space)
TEXT → Large amount of text data

👉 Best for storing names, emails, addresses, etc.

3. Date and Time Data Types

DATE → Stores year, month, day (e.g., 2025-08-16)
TIME → Stores only time (e.g., 10:30:45)
DATETIME / TIMESTAMP → Stores both date and time

👉 Useful for logging order dates, timestamps, and scheduling events.

4. Other Data Types

BOOLEAN → True/False values
BLOB → Binary data like images or files

🔹 My Example: Hospital Database

Here’s a sample hospital table I created using SQL data types:

CREATE TABLE Hospital (
    hospital_id INT,
    hospital_name VARCHAR(100),
    established_date DATE,
    total_beds INT,
    available_beds INT,
    city VARCHAR(50)
);

Now, let’s add some operator-based queries:

✅ Arithmetic Operator Example

Find occupied beds and bed occupancy percentage:

SELECT 
    hospital_name,
    total_beds,
    (total_beds - available_beds) AS occupied_beds,
    ((total_beds - available_beds) * 100 / total_beds) AS occupancy_percentage
FROM Hospital;

✅ Comparison Operator Example

Find hospitals in Chennai:

SELECT * 
FROM Hospital 
WHERE city = 'Chennai';

✅ Logical Operator Example

Find hospitals with more than 100 beds AND located in Chennai:

SELECT * 
FROM Hospital 
WHERE total_beds > 100 AND city = 'Chennai';

This way, I not only learned the theory but also applied it with real-life hospital data.

🔹 SQL Operators

Operators are used inside SQL queries to perform operations on data.

1. Arithmetic Operators

Used for mathematical calculations.

+ (Addition) → SELECT 5+3; → 8
- (Subtraction) → SELECT 10-4; → 6
* (Multiplication) → SELECT 4*2; → 8
/ (Division) → SELECT 20/5; → 4
% (Modulo) → SELECT 10%3; → 1

2. Comparison Operators

Used for comparing values in conditions.

= → Equal to
<> or != → Not equal
> → Greater than
< → Less than
>= → Greater than or equal to
<= → Less than or equal to

👉 Example:

SELECT * FROM employees WHERE salary > 50000;

3. Logical Operators

Used to combine conditions.

AND → Both conditions must be true
OR → At least one condition must be true
NOT → Negates a condition