![]() ![]() ĮND Code language: SQL (Structured Query Language) ( sql ) To create a new trigger in SQLite, you use the CREATE TRIGGER statement as follows: CREATE TRIGGER trigger_name In addition, you use triggers to enforce complex business rules centrally at the database level and prevent invalid transactions. For example, you want to log the changes in the sensitive data such as salary and address whenever it changes. You often use triggers to enable sophisticated auditing. What is an SQLite triggerĪn SQLite trigger is a named database object that is executed automatically when an INSERT, UPDATE or DELETE statement is issued against the associated table. This article has shown you how to work with a SQLite Database.Summary: this tutorial discusses SQLite trigger, which is a database object fired automatically when the data in a table is changed. query = pd.read_sql(f'SELECT Car, MPG, Cylinders FROM LIMIT 5', conn) When executing a SELECT query, this task can be performed using the read_sql() function and passing it two (2) arguments, a SQL statement and a Connection Object ( conn). Paste the following lines to the bottom of the cars-sql.py file. This section shows how to create and execute a SELECT query. □ Note: The commit() command saves changes invoked by a SQL query to the database. If output to the terminal, the following would display. This action retrieves the Field Names from the Table and saves the results to tbl_fields. The following lines access and retrieve the scription field using a lambda, a map(), and a list. A Cursor Object is created from these results and saved to cols. The first two (2) lines in the above code snippet execute and commit a SQL command that receives all rows from the inventory Table. cols = conn.execute('SELECT * FROM inventory')Ĭol_names = list(map(lambda x: x, scription)) This section shows how to retrieve a list of the Column Names in the Table. ![]() If successful, the cars.db SQLite database should now reside in the current working directory. The Cursor Object allows access to commands, such as SQL, which can be applied against the Database and/or Table. The last line creates a Cursor Object ( cur) from the Connection Object ( conn). Then the contents of df are imported into the table specified earlier ( inventory).The cars.csv file is read in (notice the separator character).A Database is created, and a Connection object to the same saves to conn.If the Database does not exist, code execution falls inside the else statement where the following occurs: If this file exists, a Connection Object is created ( conn), allowing access to the Database (shown below). The first line in the above code snippet checks to see if the Database exists in the current working directory ( cars.db). This section does all the heavy lifting! It creates a Database if it does not already exist and attempts to connect to the same! This section creates and assigns variables for the Database, its associated Table, and the cars.csv file downloaded earlier. The last line also imports Python’s built-in os library that checks for the existence of the Database file. The following line imports Python’s built-in sqlite3 library required to access and manipulate the SQLite database. The first line in the above code snippet calls in the pandas library, which is required to access and manipulate the cars.csv file downloaded earlier. import pandas as pdįrom os.path import exists as file_exists Next, create a Python file in the current working directory called cars-sql.py and paste the following code to the top of this file. The first step is to import and install the required library to ensure the code in this article will run error-free. We can accomplish this task by performing the following these steps: □ Question: How would we write code to create and work with a SQLite Database ? ![]()
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