📚 SQL Data Types: NUMBER, CHAR, VARCHAR2, DATE, TIMESTAMP

SQL data types define what kind of data a column can hold. Below are common data types with Bangladeshi examples and real-life use cases.

🔢 1️⃣ NUMBER

Syntax: NUMBER(p, s)

Explanation: Stores numeric values.

p = precision (total digits)
s = scale (digits after decimal)

salary NUMBER(8, 2)  -- Example: 50000.00

Use Case: Employee salary, product price, tax, etc.

🔤 2️⃣ CHAR

Syntax: CHAR(n)

Explanation: Fixed-length string. Always takes up n characters, padding with spaces if needed.

gender CHAR(1)  -- Example: 'M' or 'F'

Use Case: Gender, grade, status flags.

✍️ 3️⃣ VARCHAR2

Syntax: VARCHAR2(n)

Explanation: Variable-length string. Efficient for names, emails, and addresses.

name VARCHAR2(100)  -- Example: 'Nasrin Akter'

Use Case: Names, emails, project titles.

📅 4️⃣ DATE

Stores: Date and time (up to seconds)

hire_date DATE  -- Example: '2023-06-15'

Use Case: Birth date, hire date, order date.

⏱️ 5️⃣ TIMESTAMP

Stores: Date and time with fractional seconds (more precision than DATE)

created_at TIMESTAMP  -- Example: '2023-07-26 14:45:23.540'

Use Case: Logging exact event time, audit trails.

📋 Example Table: employees

CREATE TABLE employees (
  id NUMBER PRIMARY KEY,
  name VARCHAR2(100),
  gender CHAR(1),
  salary NUMBER(8, 2),
  hire_date DATE,
  created_at TIMESTAMP
);

🧠 Sample Row:

INSERT INTO employees VALUES (
  1,
  'Rafiul Islam',
  'M',
  55000.00,
  TO_DATE('2022-01-10','YYYY-MM-DD'),
  SYSTIMESTAMP
);

📌 Summary:
Use NUMBER for numeric values, CHAR for fixed small strings, VARCHAR2 for variable text, DATE for date/time, and TIMESTAMP for precise logging.

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📚 SQL Data Types Explained