Join Bill Weinman for an in-depth discussion in this video Updating a table with a trigger, part of SQL Essential Training (2014).
…Triggers are operations that are automatically…performed when a specified database event occurs.…A common use for triggers is to force a table to…be updated whenever a row is inserted or updated in another table.…How triggers are implemented and used,…varies significantly from system to system.…The lessons in this chapter are intended as an overview to give you a sense…of how triggers work, for this lesson…we're going to be using the test.db database.…And I'm going to copy and paste some statements from the Chap09 Exercise Files.…
We're going to start by creating a couple of…tables and inserting some rows into the tables.…So, I'll copy that and paste it into the SQL box here in SID, and press Go.…And you see we created two tables.…A widgetCustomer table and a widgetSale table.…They have automatically updating id columns.…And in the customer table there's a name column…and a last_order_id which you see is NULL for now.…And the sale table has a place for the customer_id which…will link it to the customer table and quantity, and price.…
- Understanding SQL terminology and syntax
- Creating new tables and records
- Inserting and updating data
- Writing basic SQL queries
- Sorting and filtering
- Accessing related tables with JOIN
- Working with strings
- Finding the numeric type of a value
- Using aggregate functions and transactions
- Updating a table with triggers
- Creating views
Skill Level Beginner
Q: For Mac OS X: When I try to start the Apache Web Server from the XAMPP control panel, it doesn't start, and when I open "localhost" in my web browser, I see a white screen that says "It Works!" instead of the XAMPP page.
sudo apachectl stop
Q: I'm on a Mac, and I get an error in SID that says "attempt to write a read only database." How can I fix this?
A: This usually means that the database folder does not have sufficient permissions for writing by the web user. This can happen if you create the SQL folder new, rather than copying it from the Exercise Files. Here's how to fix this:
- Open a Finder window and Navigate to /Applications/XAMPP/htdocs/SQL
- Control-click on the SQL folder and select "Get Info" from the context menu.
- Under "Sharing and Permissions" (you may need to open the disclosure triangle), in the "everyone" row, select "Read & Write."Then you can close the Info window.
- Now repeat the process for the three *.db files inside the folder.
1. SQL Quick Start
Understanding joins2m 23s
Dates and times1m 59s
10. Subselects and Views
11. A Simple CRUD Application
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