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MySQL Essential Training
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Creating a stored function


From:

MySQL Essential Training

with Bill Weinman

Video: Creating a stored function

A stored function is defined with the create function statement. Duration from track.
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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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MySQL Essential Training
4h 24m Beginner May 14, 2014

Viewers: in countries Watching now:

MySQL is by far the most popular database management system for small- to medium-sized web projects. In this course, Bill Weinman provides clear, concise tutorials that guide you through creating and maintaining a MySQL database of your own. Bill explores the basic syntax, using SQL statements to create, insert, update, and delete data from your tables. He also covers creating a new database from scratch, as well as data types, transactions, subselects, views, and stored routines. Plus, learn about the multi-platform PHP PDO interface that will help you connect your database to web applications.

Topics include:
  • Writing queries
  • Creating and updating databases and tables
  • Using MySQL built-in functions
  • Sorting and filtering data
  • Updating tables with triggers
  • Working with subselects and views
  • Creating and using a stored function
Subjects:
Developer Databases
Software:
MySQL
Author:
Bill Weinman

Creating a stored function

A stored function is defined with the create function statement. For this exercise we'll be using the album data base. MySQL provides a function for converting seconds to time, but I usually need to reformat it as a string anyway, so I tend to use a stored function like this one. Create function, and we'll call this track_len. And it takes one parameter, seconds and it's an integer. It returns a VARCHAR and it's not a very long one so 16 bytes will do.

And it's deterministic, what deterministic means is that this function will always return the same value for the same input. And tagging it as deterministic like this, helps the optimizer in MySQL to create more efficient code. The default is not deterministic, so you want to put this in if your code is going to always return the same value for the same input, and this certainly will. Return concat with separator and uses a colon for separator and starts with seconds DIV 60.

So that's the minutes part, and then we're going to use LPAD, which is a string function that pads the left side of a string. And we'll have a pad with zeros to a fixed length of two so it's always got that leading zero. If it's just one digit second, if it's two digit seconds, it doesn't need the leading zero, so LPAD does this beautifully. And we'll use seconds MOD 60, which is just the seconds part without the minutes. It's the remainder after the division by 60.

And it's two in length, and it pads with a zero. And we need two parenthesis here, one for the LPAD and one for the CONCAT WS. And a semicolon. So we've now created our function and all we need to do to use it is say select title track or track_len. Use our function here. Duration from track. Like that. And when I press Go, we've now used this function.

There it is. And you see that the minutes are not padded, but the seconds are. We have 08 seconds there, so it's got that leading zero, right? So that time has been converted to a string. And now that the function is created. Every time we use it, we will get that same result. And there we are. So I like the way this formats the time, with the leading zeros for the seconds, but not for the minutes. The beauty of this approach though is that if you don't like it, you can easily change it and you only need to change it in one place.

wherever this function is used, it will be updated when you change it. For the next example, I'm going to, just go ahead and grab it here from the exercise files. And this is the chapter nine exercise file. I'm just copying, and pasting, this second select statement here. We'll paste that in, and we'll see. This is a nice listing of all the tracks for all the albums in the database and we have this nice little JOIN query and you notice that I'm using my track_len function there for the length column.

And that's just really convenient and easy to do. Now, stored functions are not used in aggregate context. You cannot use this. As an aggregate function. But you can use it with the result of an aggregate function. So, I'm going to go and grab this next example here from the exercise file. And I'll paste that in and press go. And here we have the total length of each of the albums in the database. And the way that's working, is this is, you see we have a group eye, so it is an aggregate context.

But we have the sum function here and track link is simply processing the result of sum. And so track link is technically not being used in an aggregate context, although. The value that it is processing is an aggregate value. So, that works just fine. And that's a great way to get around this limitation. So, I'm going to leave this stored function in place. We're going to use it in the next lesson. A stored function is a very powerful and convenient tool. It's easy to define and to use.

And allows you increased control over the functionality of your systems.

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