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Enumeration types

From: MySQL Essential Training

Video: Enumeration types

MySQL provides two unique types that work from lists of strings. So ENUM works from a list of strings, and the column And you can see in these rows down here we have more than one value from the list.

Enumeration types

MySQL provides two unique types that work from lists of strings. So let's learn about them using the scratch data base and start by creating a table. And of course I will drop table if exists, and we'll call it test. Create table test. I'll have an id column and ENUM column. So ENUM works from a list of strings, and the column can hold in each row one of these strings in the list.

And so I'll give it a list of strings here. Pablo, Henri, and Jackson. And no comma after that last column in the definition. And so we can insert into test, values. And so I can put Pablo, Henri, or Jackson, but no other string's valid in this column. And then we'll select star from test, and press go. So here we have three rows, and column haze Pablo, Henri, and Jackson.

Now, what's interesting here, it's actually being stored. Because we could have a lot of columns. We could do this again, we could just copy and paste these three again. And I now have six rows. Right? I can have these same values many times throughout them. And I don't need to store these strings over and over again. In fact, all that this column is storing is numbers. If, instead of Pablo here, I put in a one. And instead of Henri, I put in a two. And instead of Jackson, I put in a three.

The result is the same. Because really all that's being stored in the ENUM column, is an index into this table of strings. So I can have a bunch of these, and I could have four, five, six, seven. And, each of these rows in that column is just holding a number that represents an index into that list of strings. So, it's a space-saving tool. And it's also a bit of a constraint tool, because you're only going to have the values that you've defined in the table.

So, that's ENUM. SET, works very similarly, and I'm just going to change this to SET. And we'll use exactly the same. We just have, Pablo, Henri and Jackson. And I'm going to say Go. And it looks like our result is exactly the same. But there's a very distinct difference. I'm going to, copy this. And, put a few more of them here. And I can have Pablo and Jackson in the same row.

In that one column, I can have Henri and Jackson, or I can have Pablo, Henri, and Jackson. And you can see in these rows down here we have more than one value from the list. So the distinction here is rather than how ENUM works, where each of these rows for this column holds a number that represents an index into this string. Instead, with SET, each bit in this value represents one of these strings.

So, if I come down here, I'm going to take this one. And I'm going to copy and paste it three more times. And I'm going to put in the value one, and I'm going to put in the value two, and now I'm going to put in the value three, and actually let's keep going four, five, six and seven. Because you'll notice we have. Three strings to find. So three bits are actually being defined here, and there are seven possible values with three bits.

And so I'm going to say go here and what we have is a one is Pablo. Two is on Henri. Three is both of those first two bits set, and so that's Pablo and Henri. Four is just that third bit set. And that's Jackson. Five, the first and the third bit. Six, the second and the third bit. And seven, all three bits are set. So each bit represents one of these strings. That's the distinction between SET and ENUM.

So if you know you're going to have a limited number of possible values in a column, it can be much more economical to store an index. As in an ENUM than many copies of the same string. Likewise if you need to store more than one from a set of possible values. A set can be economical as well. And a set may also be useful for storing flags and State indicators.

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This video is part of

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MySQL Essential Training

60 video lessons · 7122 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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