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Python SQLAlchemy - Write a query where a column contains a substring

Last Updated : 15 Feb, 2022
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In this article, we discussed how to extract the column values containing substring in SQLAlchemy against a PostgreSQL database in python.

In SQLAlchemy, generic functions like SUM, MIN, MAX, are invoked like conventional SQL functions using the func attribute. 

Some common functions used in SQLAlchemy are contains, count, cube, current_date, current_time, max, min, mode etc.

Usage: func.sum(). func.group_by(), func.sum()

Creating table for demonstration

Import necessary functions from the SQLAlchemy package. Establish connection with the PostgreSQL database using create_engine() function as shown below. Create a table called books with columns book_id and book_price. Insert record into the tables using insert() and values() function as shown.

Python3 
# import necessary packages
import sqlalchemy
from sqlalchemy import create_engine, MetaData, 
Table, Column, Numeric, Integer, VARCHAR
from sqlalchemy.engine import result

# establish connections
engine = create_engine(
    "database+dialect://username:password@hostname:port/databasename")

# initialize the Metadata Object
meta = MetaData(bind=engine)
MetaData.reflect(meta)

# create a table schema
books = Table(
    'books', meta,
    Column('book_id', Integer, primary_key=True),
    Column('book_price', Numeric),
    Column('genre', VARCHAR),
    Column('book_name', VARCHAR)
)

meta.create_all(engine)

# insert records into the table
statement1 = books.insert().values(book_id=1, 
                                   book_price=12.2,
                                   genre='fiction', 
                                   book_name='Old age')

statement2 = books.insert().values(book_id=2,
                                   book_price=13.2,
                                   genre='non-fiction', 
                                   book_name='Saturn rings')

statement3 = books.insert().values(book_id=3,
                                   book_price=121.6,
                                   genre='fiction',
                                   book_name='Supernova')

statement4 = books.insert().values(book_id=4, 
                                   book_price=100,
                                   genre='non-fiction', 
                                   book_name='History of the world')

statement5 = books.insert().values(book_id=5, 
                                   book_price=1112.2,
                                   genre='fiction', 
                                   book_name='Sun city')

# execute the insert records statement
engine.execute(statement1)
engine.execute(statement2)
engine.execute(statement3)
engine.execute(statement4)
engine.execute(statement5)

Output:

Sample table

Extract column values by substring by in SQLAlchemy

sqlalchemy.select([
Tablename.c.column_name,
sqlalchemy.func.sum(Tablename.c.column_name)
]).group_by(Tablename.c.column_name)

Get the books to table from the Metadata object initialized while connecting to the database and pass the SQL query to the execute() function and get all the results using fetchall() function. Use a for loop to iterate through the results.

This SQL query returns the names of the book containing the substring "fiction" in the genre column.

Python3 
# Get the `books` table from the Metadata object
BOOKS = meta.tables['books']

# SQLAlchemy Query to pick
# records containing substring fiction
query = sqlalchemy.select([
    BOOKS.c.book_name,
]).filter(BOOKS.c.genre.contains("fiction"))


# Fetch all the records
result = engine.execute(query).fetchall()

# View the records
for record in result:
    print("\n", record)

Output:

The output of column containing a substring

J
jssuriyakumar
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