Join Bill Weinman for an in-depth discussion in this video Preventing automatic updates with a trigger, part of SQL Essential Training (2014).
…Triggers may also be used to prevent changes to rows that…have already been reconciled or should not be changed for other reasons.…For this reason, we're going to use the test.db database.…And I'm going to be copying and pasting from the chapter nine…exercise files, here around line 125 where it says O2 preventing updates.…We're using the tables from the previous lesson.…I'm actually going to drop one of them…first here and recreate it ,with this reconciled…column which will be used to determine if a row should be updated or not.…
So I'll select all of that and actually we're going to select all…of this all the way down to the end of the create trigger.…And I'll copy and past that into our SQL box and run it.…So we've recreated this table.…We dropped it and then recreated it and inserted three rows into it and ran a…select so you can see what the table…looks like there, and then we created this trigger.…The create trigger statement creates the trigger with the…name update widget sales, that's the name of the trigger.…
- 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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