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Logging transactions with a trigger

From: MySQL Essential Training

Video: Logging transactions with a trigger

In this example, I'll show you how to use a trigger to update a transaction log. And we select everything from sale customer and log there at the end.

Logging transactions with a trigger

In this example, I'll show you how to use a trigger to update a transaction log. I'm going to start by copying and pasting from the chapter seven exercise file. We're going to be using the scratch database here. And I'm continuing with the tables that were created earlier in the chapter. If you happen to be following along, you can just create these tables from the. Exercise file and you should be fine. So, I'm going to come down here to, Lesson Number three, logging transactions with a trigger. And we're going to copy everything from here on down to here.

First, I'll take a moment to describe it. We're going to recreate the sale table and in this case we're just doing this to get rid of that reconciled flag that we used in the last movie. And we're going to keep the customer table which already has those three records in it for. Bob and Sally and Fred, and then we're going to create this trigger again. We're using the delimiter, to change the delimiter because we have multiple statements here in our trigger. So this allows all of this to be submitted to the database engine as one unit.

And again, this is a very MySQL specific paradigm. The trigger itself is an after insert trigger, so when you insert a row in widget sale, this trigger will be triggered and this code will be executed. And you notice we insert three rows here into the sale table. So between begin and end we have a block of code with two statements in it. The first one, sets the last order ID in customer like we did in the first example and the second one, inserts into the widget log to log the event.

Now you notice the log table here has a serial. Has a time stamp so it automatically. Sets the time according to whatever time it is and it has a string for the event, a string for the user name, a string for the table name and a table id for that table that's named so widget sale will get that new id from the sale row that's being inserted into the sale table. So, it's very simple code here. And I'm going to go ahead and copy and paste.

And we select everything from sale customer and log there at the end. So I'll paste this into the sid here. And we'll go ahead and execute it, so we have these tables in this order sale, customer and logs so here's the sale, and we just created the three sale rows in here. And there's the customer you see the last order ID has been updated with those sales. And here's our log table. So we have the stamp, the event, it was an insert. The user name trigger. And the sale table, and the table ID.

So we inserted three rows, row one, two, and three from the sale table. And you can link back to those in the sale table, and see exactly what they are. So very simple technique. For updating a log whenever a row is inserted into a table. You can use triggers for many purposes. Here, I've shown you how to update two tables from one trigger including a new row and a transaction log table. And, updating this customer table with the last order ID.

And so just to finish off this lesson, I'm going to drop all of our triggers and tables. In actuality, the only one of these triggers that still exist is the widget log, because every time you drop a table. The triggers associated with that table are automatically dropped. But just so that you can see how it's done, you can drop triggers with the drop trigger statement. And, just like you drop tables with the drop table statement, I'm going to copy and paste all of that. In to our SQL box here and execute it so that all of that is actually cleaned up for the rest of the course.

It's also worth noting that in other systems where they don't automatically drop a trigger, you can get an error if you drop a table before you drop the associated trigger, so I always drop the triggers first before I drop the associated tables.

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This video is part of

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MySQL Essential Training

60 video lessons · 5524 viewers

Bill Weinman
Author

 
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  1. 4m 22s
    1. Welcome
      1m 3s
    2. Using the exercise files
      1m 31s
    3. What is MySQL?
      1m 48s
  2. 45m 37s
    1. Installation overview
      3m 16s
    2. Installing XAMPP on Windows
      5m 55s
    3. Installing XAMPP on the Mac
      6m 38s
    4. Setting up MySQL users
      11m 31s
    5. Installing SID on Windows
      5m 43s
    6. Installing SID on the Mac
      6m 6s
    7. Installing time zone support in MySQL on Windows
      6m 28s
  3. 45m 43s
    1. The SELECT statement
      3m 57s
    2. Selecting rows
      4m 57s
    3. Selecting columns
      3m 8s
    4. Sorting results with ORDER BY
      2m 58s
    5. Filtering results with WHERE
      3m 52s
    6. Filtering results with LIKE and IN
      3m 41s
    7. Filtering results with regular expressions
      8m 21s
    8. Inserting rows
      4m 9s
    9. Updating rows
      2m 21s
    10. Deleting rows
      2m 25s
    11. Literal strings
      3m 12s
    12. Understanding NULL
      2m 42s
  4. 41m 47s
    1. Creating a database
      4m 30s
    2. Creating a table
      7m 18s
    3. Creating indexes
      6m 8s
    4. Controlling column behavior with constraints
      4m 46s
    5. Creating an ID column
      6m 58s
    6. Using foreign key constraints
      7m 58s
    7. Altering a table
      4m 9s
  5. 28m 56s
    1. What are data types?
      4m 1s
    2. Numeric types
      5m 21s
    3. String types
      2m 58s
    4. Date and time types
      7m 2s
    5. Bit type
      2m 26s
    6. Boolean values
      2m 15s
    7. Enumeration types
      4m 53s
  6. 32m 34s
    1. String functions
      6m 57s
    2. Numeric functions
      6m 2s
    3. Date and time functions
      4m 12s
    4. Time zones in MySQL
      3m 37s
    5. Formatting dates
      1m 51s
    6. Aggregate functions
      5m 45s
    7. Flow control with CASE
      4m 10s
  7. 7m 6s
    1. Maintaining database integrity with transactions
      4m 46s
    2. Using transactions for performance
      2m 20s
  8. 16m 49s
    1. Updating a table with a trigger
      5m 11s
    2. Preventing automatic updates with a trigger
      7m 29s
    3. Logging transactions with a trigger
      4m 9s
  9. 14m 11s
    1. Creating a simple subselect
      3m 23s
    2. Searching within a result set
      3m 53s
    3. Creating a view
      3m 32s
    4. Creating a joined view
      3m 23s
  10. 12m 26s
    1. Understanding MySQL stored routines
      2m 0s
    2. Creating a stored function
      4m 34s
    3. Creating a stored procedure
      5m 52s
  11. 14m 4s
    1. The multi-platform PDO interface
      3m 44s
    2. Executing the SQL
      4m 8s
    3. Implementing auto-increment IDs
      2m 3s
    4. Using a stored funciton
      4m 9s
  12. 1m 3s
    1. Goodbye
      1m 3s

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