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 β 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.
πΉ 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
β Whole numbers (e.g., 10, -5, 1000) -
DECIMAL(p,s)
β Fixed precision decimal values (e.g., 123.45) -
FLOAT
/REAL
β Approximate decimal values (e.g., 3.14159)
π Used when storing things like age, salary, or percentage.
2. Character/String Data Types
-
CHAR(n)
β Fixed-length string (e.g.,'RAMYA '
with length 5) -
VARCHAR(n)
β Variable-length string (saves space) -
TEXT
β Large amount of text data
π Best for storing names, emails, addresses, etc.
3. Date and Time Data Types
-
DATE
β Stores year, month, day (e.g.,2025-08-16
) -
TIME
β Stores only time (e.g.,10:30:45
) -
DATETIME
/TIMESTAMP
β Stores both date and time
π Useful for logging order dates, timestamps, and scheduling events.
4. Other Data Types
-
BOOLEAN
β True/False values -
BLOB
β Binary data like images or files
πΉ My Example: Hospital Database
Hereβs 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, letβs add some operator-based queries:
β 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;
β Comparison Operator Example
Find hospitals in Chennai:
SELECT *
FROM Hospital
WHERE city = 'Chennai';
β 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.
πΉ SQL Operators
Operators are used inside SQL queries to perform operations on data.
1. Arithmetic Operators
Used for mathematical calculations.
-
+
(Addition) βSELECT 5+3;
β 8 -
-
(Subtraction) βSELECT 10-4;
β 6 -
*
(Multiplication) βSELECT 4*2;
β 8 -
/
(Division) βSELECT 20/5;
β 4 -
%
(Modulo) βSELECT 10%3;
β 1
2. Comparison Operators
Used for comparing values in conditions.
-
=
β Equal to -
<>
or!=
β Not equal -
>
β Greater than -
<
β Less than -
>=
β Greater than or equal to -
<=
β Less than or equal to
π Example:
SELECT * FROM employees WHERE salary > 50000;
3. Logical Operators
Used to combine conditions.
-
AND
β Both conditions must be true -
OR
β At least one condition must be true -
NOT
β Negates a condition
π Example:
SELECT * FROM students
WHERE grade = 'A' AND age < 20;
4. Special Operators
-
BETWEEN
β Check range (age BETWEEN 18 AND 25
) -
IN
β Match values in a list (city IN ('Chennai','Bangalore')
) -
LIKE
β Pattern matching (name LIKE 'R%'
) -
IS NULL
β Check missing values
πΉ Key Takeaway
β
Data types ensure that each column stores the right kind of information.
β
Operators help us filter, calculate, and manipulate data effectively.
β
Building my hospital database gave me hands-on practice with both concepts.
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