[파이썬] SQLAlchemy Function-based Index 생성

06 Sep 2023

SQLAlchemy

In relational databases, indexes are crucial for improving query performance. SQLAlchemy, a popular Object Relational Mapping (ORM) library in Python, provides various ways to create indexes. One of the options is to create function-based indexes.

A function-based index is an index that is created based on the result of a function or expression. It allows you to create indexes on computed or derived values, providing more flexibility in optimizing your queries.

In this blog post, we will explore how to create function-based indexes using SQLAlchemy.

Prerequisites

To follow along with this tutorial, make sure you have the following installed:

Python (version 3.6 or above)
SQLAlchemy library

You can install the SQLAlchemy library using pip:

pip install sqlalchemy

Creating a Function-based Index

To create a function-based index with SQLAlchemy, you need to define a custom DDL (data definition language) construct. SQLAlchemy provides the Ddl class for this purpose.

Let’s say we have a table called users with the following columns:

from sqlalchemy import create_engine, Column, Integer, String
from sqlalchemy.dialects.postgresql import ARRAY
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    age = Column(Integer)
    skills = Column(ARRAY(String))

Now, let’s create a function-based index on the column age by applying the abs() function to it:

from sqlalchemy import text
from sqlalchemy.schema import CreateTable

index_name = "idx_users_age_abs"

index_ddl = DDL(f"CREATE INDEX {index_name} ON users (abs(age))")
index_ddl.execute(bind=engine, table=CreateTable(User.__table__))

The DDL construct allows us to execute arbitrary SQL statements. In this example, we create an index named idx_users_age_abs on the users table using the abs() function applied to the age column.

Verifying the Function-based Index

To verify if the function-based index is created successfully, you can use the SQLAlchemy inspect() function and check the indexes attribute of the Table object.

from sqlalchemy import inspect

inspector = inspect(engine)
indexes = inspector.get_indexes("users")

for index in indexes:
    print(index['name'])

You should see the name of the index idx_users_age_abs in the output if the index is created successfully.

Conclusion

In this blog post, we learned how to create function-based indexes in SQLAlchemy. By leveraging function-based indexes, you can improve query performance by creating indexes on computed or derived values. This allows for more flexibility in optimizing your database queries.