Get Column name and Column type with Python psycopg2

When working with PostgreSQL databases in Python, one common task is to retrieve metadata about database tables, such as column names and their types. This information can be crucial for dynamically generating queries, validating data, or understanding the structure of our database. The psycopg2 library provides a powerful way to interact with PostgreSQL databases from Python, including retrieving metadata about tables.

Prerequisites

Before diving into the examples, ensure we have the following prerequisites:

• PostgreSQL Installed: We need a running PostgreSQL server.
• Python Environment: Python should be installed on our system.
• psycopg2 Library: Install the psycopg2 library if it is not already installed. This library is used to connect to PostgreSQL from Python.

Install psycopg2 using pip:

pip install psycopg2

Get Column name and Column type with Python psycopg2

Let's us see a few examples of how we can get column name and column type with Python psycopg2.

Example 1: Create a Table and Retrieve Column Information

Below code connects to a PostgreSQL database, creates a table with specified columns, and then closes the connection. After reconnecting, it retrieves the column names and data types for the created table by querying the information_schema.columns, and then prints the results. Finally, it closes the cursor and connection again.

Step 1: Create a Table in PostgreSQL

import psycopg2

# Connect to your PostgreSQL database
conn = psycopg2.connect(
    dbname="your_database_name",
    user="your_username",
    password="your_password",
    host="localhost",
    port="5432"
)

# Create a cursor object
cur = conn.cursor()

# Create a table
create_table_query = """
CREATE TABLE employee (
    id SERIAL PRIMARY KEY,
    name VARCHAR(100),
    age INT,
    hire_date DATE
)
"""
cur.execute(create_table_query)
conn.commit()

print("Table created successfully")

# Close the cursor and connection
cur.close()
conn.close()

Output

Step 2: Get Column Names and Column Types

The information_schema is a standardized set of read-only views that provide metadata about the objects (such as tables, columns, and constraints) in a relational database.

The information_schema acts as a database within the database, allowing users to query metadata just like they would query regular data.

Here, we will use this information_schema database to fetch column name and column type of the table we created.

import psycopg2

# Connect to your PostgreSQL database
conn = psycopg2.connect(
    dbname="your_database_name",
    user="your_username",
    password="your_password",
    host="localhost",
    port="5432"
)

# Create a cursor object
cur = conn.cursor()

# Query to get column names and types
table_name = 'employee'
cur.execute(f"SELECT column_name, data_type FROM information_schema.columns WHERE table_name = '{table_name}'")

# Fetch all results
columns = cur.fetchall()

# Display column names and types
print("Column Name\t\tColumn Type")
print("-" * 40)
for column in columns:
    print(f"{column[0]}\t\t{column[1]}")

# Close the cursor and connection
cur.close()
conn.close()

Output

Example 2: Create a Table with Different Data Types and Retrieve Metadata

Below code connects to the PostgreSQL database, retrieves column names and data types from the information_schema.columns for a specified table, and prints them. It then closes the cursor and database connection.

Step 1: Create a Table with Different Data Types

import psycopg2

# Connect to your PostgreSQL database
conn = psycopg2.connect(
    dbname="your_database_name",
    user="your_username",
    password="your_password",
    host="localhost",
    port="5432"
)

# Create a cursor object
cur = conn.cursor()

# Create a table with various data types
create_table_query = """
CREATE TABLE product (
    product_id SERIAL PRIMARY KEY,
    product_name VARCHAR(255),
    price DECIMAL(10, 2),
    stock_quantity INT,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
)
"""
cur.execute(create_table_query)
conn.commit()

print("Table created successfully")

# Close the cursor and connection
cur.close()
conn.close()

Output

Step 2: Get Column Names and Types

import psycopg2

# Connect to your PostgreSQL database
conn = psycopg2.connect(
    dbname="your_database_name",
    user="your_username",
    password="your_password",
    host="localhost",
    port="5432"
)

# Create a cursor object
cur = conn.cursor()

# Query to get column names and types
table_name = 'product'
cur.execute(f"SELECT column_name, data_type FROM information_schema.columns WHERE table_name = '{table_name}'")

# Fetch all results
columns = cur.fetchall()

# Display column names and types
print("Column Name\t\tColumn Type")
print("-" * 40)
for column in columns:
    print(f"{column[0]}\t\t{column[1]}")

# Close the cursor and connection
cur.close()
conn.close()

Output

Use Cases

• Dynamic Query Generation: Retrieving column names and types allows us to dynamically generate queries based on the table schema, which is useful in applications where the database schema may change frequently.
• Data Validation: Knowing the data types of columns helps in validating data before insertion or modification to ensure it conforms to the expected format.
• Schema Exploration: Useful in data analysis and reporting tools to understand the structure of the database and its tables without needing prior knowledge of the schema.

Conclusion

Retrieving column names and types from a PostgreSQL database using Python and psycopg2 is a straightforward process that can be extremely valuable in various scenarios, from dynamic query generation to data validation. By following the examples provided, we can efficiently interact with PostgreSQL to obtain the metadata we need for our applications.