SQLite Essentials: Triggers, Data Management, and Python Integration

Posted on Apr 29, 2024 in Computers

SQLite Trigger

Key Points

  • Triggers are database callback functions executed automatically upon specific events (DELETE, INSERT, UPDATE).
  • SQLite supports FOR EACH ROW triggers, not FOR EACH STATEMENT triggers.
  • WHEN clause allows conditional trigger execution.
  • BEFORE or AFTER keyword determines trigger timing relative to the event.
  • Triggers are dropped automatically when their associated table is dropped.
  • The RAISE() function can be used within a trigger to raise an exception.

Trigger Syntax

CREATE TRIGGER [IF NOT EXISTS] trigger_name [BEFORE|AFTER|INSTEAD OF] [INSERT|UPDATE|DELETE] ON table_name

Setting PYTHONPATH

PYTHONPATH is an environment variable specifying directories for Python modules and packages. It’s used for custom libraries not installed in the global location.

SQLite Dump

The .dump command exports database structure and data to a text file.

Dumping the Entire Database

Use the .dump command to save the entire database to a file. Use .output FILENAME to specify the output file.

Dumping a Specific Table

Specify the table name after .dump to dump a specific table.

Dumping Table Structures Only

Use the .schema command to dump table structures.

Dumping Data of One or More Tables

  • Set mode to insert using .mode insert.
  • Set output file using .output FILENAME.
  • Use SELECT statements to query data from desired tables.

CSV File Handling

Importing a CSV File

  • Use .mode csv to set the mode to CSV.
  • Use .import FILE TABLE to import data from the CSV file into the table.

Exporting a CSV File

  • Turn on headers using .header on.
  • Set output mode to CSV using .mode csv.
  • Set output file using .output FILENAME.
  • Use SELECT statements to query data for export.

SQLite Database in Python

  1. Import the sqlite3 module.
  2. Connect to the database using connect().
  3. Create a cursor object using cursor().
  4. Execute SQL queries using execute().
  5. Fetch results using fetchall(), fetchone(), or fetchmany().
  6. Close the cursor and connection objects.
  7. Catch database exceptions.

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