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Creating an ID column

From: MySQL Essential Training

Video: Creating an ID column

An ID column, is a column that's used as a unique identifier for each row in a table. And so, in MySQL, a primary key And that's all just with this primary key here.

Creating an ID column

An ID column, is a column that's used as a unique identifier for each row in a table. It's commonly used in relational databases for connecting one table to another. For this lesson, we're going to use the scratch database, and again I'm going to copy from the exercise files. This is the, chapter 3 exercise file starting around line 100. Starting with this drop table if exists, because again, we're going to be creating this table over and over again with different options all the way down here through show indexes from tests on line 113.

So, I'm going to to copy that and paste that to our. SQL box here. And you'll notice I'm creating a table with three columns, INTEGER and two VARCHARs. And I'm inserting some rows into it and then selecting from it. I'm going to describe it, show the table status, the create table. And show the indexes. And so when I press go, there's our table, with the three rows that I inserted. They have values of one, two, and three for the ID.

And there's our describe, so that's the describe right there. The show table status. And the show create table. And you notice I also have a Show Indexes, but that's not getting us any results yet. So, I'm going to change this CREATE TABLE here, as we move along. In MySQL an ID column requires that a column is defined with not null and unique index constraints. And so, in MySQL, a primary key constraint, and this is actually true of many.

Database systems. Primary key provides both not and all, and unique. And it provides an index named primary. The effect is that there is only one primary key allowed per table. And so I'm going to go ahead and execute this. And you'll notice that down here in our show create table, it shows our create table as having a non-null constraint and a separate primary key index. And down here in our show indexes, we have a key name of primary.

And that's all just with this primary key here. We didn't say not null, we didn't say unique. So, you'll notice that nulls are not allowed and our index says, non_unique is zero, which means that it's constrained to unique keys. So if, I try to insert a duplicate row, I'm just going to. Copy this row here. So, we have two of those with a three in here twice. You notice we get a constraint violation. Duplicate entry three for key primary. So that is in fact not allowed.

So, primary key gives us those requirement for an id field. Current versions of MySQL do not require that the id column uses the primary key constraint. Earlier versions of mysql did require that. In most cases, an id column fits the definition of a primary key. Because, the id column requires that every value is unique, mysql provides a feature that will automatically generate sequential values for the column. So if, I come back up here to my definition,.

Where I have Primary Key, I can say Auto Increment. And it's a very common construct here. Auto Increment Primary Key. And when I press Go, you notice in the describe it now says auto-increment in that Extras column. And there's an Auto Increment here in the Show Table Status. And if, I come back here now and I take these values out, and I have to take ID out of the list there as well. So now I'm not inserting anything into that ID column at all, and I pressure go, and I still get those sequential values.

Those are now automatically generated. So, that's AUTO_INCREMENT. MySQL provides an alias for all of this called SERIAL. I can take all of this INTEGER_AUTO_INCREMENT_PRIMARY_KEY and I can just type SERIAL. And press Go. And I get exactly the same result. The difference here is, is that the type here, is bigint(20) unsigned. And if I say, INTEGER. Auto increment, primary key.

You notice it's just an inta 11. So, if you have a lot of data and if you're expecting to have a very large table that big int unsigned is going to give you the maximum amount of space. For those values. They'll allow you the maximum size of numbers for that column, so it's not such a bad idea. The serial short cut is an easy short cut, but you need to take your data storage requirements into consideration. In most cases, it's fine and allows for very large tables.

In practice, in an application where you might be concerned with the extra storage you'll probably need the maximum size of a ___ anyway. According to the MySQL manual serial is just an alias for bigint, unsigned, not null, auto_increment, unique. Serial was added in MySQL 4.1, so it's not available in all the older versions. So, most people still use integer primary key. When you're using an automatically generated ID, sometimes. You'll need to know the ID column for the last inserted row.

This is available from a special function. And I'm going to come down here right after the select from test. And the special function is called last insert ID. And you notice that, I'm not specifying that it comes from a particular table, this is a database wide last inserted ID, so if you're using this in code and you want to get, what's the ID of this row that I just inserted, so that you can use that ID. For another purpose. You want to be right after your inserts.

So, when I press go here, you see the last insert ID is 3, and you see that that is the ID of the last inserted row in the table. Just one more quick thing I wanted to show you with this ID serial. You'll notice that our create table shows the ID as 20, unsigned, not null, auto increment. And with the unique key ID, and here the key is named ID is not named primary because we're not using the primary key constraint. So, just so you know, that that's what it does.

My scale provides comprehensive support for ID columns with the auto increment constraint and the special serial alias. This is a very useful feature, we'll be using it a lot in the rest of the course. I'm going to go ahead and drop this table now. Bring our database back to its original state for the rest of the course.

Show transcript

This video is part of

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MySQL Essential Training

60 video lessons · 7049 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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