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230 lines
3.3 KiB
230 lines
3.3 KiB
# Python + SQL
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## Lessons
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1. Install a Python virtual environment
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1. Install psychopg2-binary
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1. Connect to Postgres via Python
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1. Running Queries with Python
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1. SQLite Basics
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1. Migrating data to a SQLite
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1. CSV Basics
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1. Exporting data to CSV
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## Install a Python virtual environment
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```python
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python3 -m venv ~/my-env
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source ~/my-env/bin/activate
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```
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## Install psychopg2-binary
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```
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python -m pip install psycopg2-binary
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```
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## Connect to Postgres via Python
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```python
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import psycopg2
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conn = psycopg2.connect(
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database="my_db"
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)
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# close connection
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conn.close()
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```
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## Running Queries with Python
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Select many
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```python
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cursor = conn.cursor()
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cursor.execute("SELECT * FROM people")
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print(cursor.fetchall())
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# close connection
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cursor.close()
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```
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Select one
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```python
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cursor.execute("SELECT * FROM people WHERE id = %s", [24])
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print(cursor.fetchone())
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```
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Insert
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```python
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cursor.execute("INSERT INTO people (name, age) VALUES (%s, %s)", ['Matt', 43])
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conn.commit()
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```
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Delete
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```python
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cursor.execute("DELETE FROM people WHERE id = %s", [24]);
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conn.commit()
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```
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Update
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```python
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cursor.execute("UPDATE people SET name = %s, age = %s WHERE id = %s", ['Matt', 43, 20])
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conn.commit()
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```
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## SQLite Basics
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Connect:
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```python
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import sqlite3
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con = sqlite3.connect("mydb.db")
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# close connection
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con.close()
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```
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Create table
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```python
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cur = con.cursor()
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cur.execute("CREATE TABLE people (name, age)")
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```
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Select Many
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```python
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res = cur.execute("SELECT * FROM people")
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print(res.fetchall())
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```
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Select One
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```python
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res = cur.execute("SELECT * FROM people WHERE name = 'Matt'")
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print(res.fetchone())
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```
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Insert
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```python
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cur.execute("INSERT INTO people (name, age) VALUES (?, ?)", ['Zagthorp', 543])
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con.commit()
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```
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Delete
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```python
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cur.execute("DELETE FROM people WHERE name = ?", ['Bilbo'])
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con.commit()
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```
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Update
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```python
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cur.execute("UPDATE people SET name = ? WHERE name = ?", ['Bilbo', 'Matthew'])
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con.commit()
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```
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Check via `sqlite3` in the terminal
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```
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sqlite3 mydb.db
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```
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## Migrating data to a SQLite
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```python
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# PostgreSQL
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import psycopg2
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conn = psycopg2.connect(
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database="my_db"
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)
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cursor = conn.cursor()
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cursor.execute("SELECT * FROM people")
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people = cursor.fetchall()
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cursor.close()
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conn.close()
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# SQLite
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import sqlite3
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con = sqlite3.connect("mydb.db")
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cur = con.cursor()
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cur.execute("CREATE TABLE people (id, name, age)")
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for person in people:
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cur.execute("INSERT INTO people (id, name, age) VALUES (?, ?, ?)", [person[0], person[1], person[2]])
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con.commit()
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con.close()
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```
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## CSV Basics
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mydb.csv:
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```csv
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1,matt,43
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2,sally,34
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3,zagthorp,999
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```
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read:
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```python
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import csv
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with open('mydb.csv', newline='') as csvfile:
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people = csv.reader(csvfile, delimiter=',')
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for person in people:
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print(person)
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```
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wrte:
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```python
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import csv
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with open('writedb.csv', 'w') as csvfile:
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writer = csv.writer(csvfile)
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writer.writerow([1, 'matt', 43])
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```
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## Exporting data to CSV
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```python
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# PostgreSQL
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import psycopg2
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conn = psycopg2.connect(
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database="my_db"
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)
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cursor = conn.cursor()
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cursor.execute("SELECT * FROM people")
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people = cursor.fetchall()
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cursor.close()
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conn.close()
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# CSV
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import csv
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with open('writedb.csv', 'w') as csvfile:
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writer = csv.writer(csvfile)
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for person in people:
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writer.writerow(person)
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```
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