In the English dictionary, alter means to change, however, alter in SQL does not mean the same thing.
SQL is used to communicate with databases and is the known standard language for database management systems. The statements used in SQL are utilized to perform tasks such as updating data or retrieving data.
To put it simply it is just the common lingo for databases and allows you to handle information via tables, and so on.
Alter ties into all this, and for anyone using SQL, it is very handy and useful.
However, there is much to know about alter.
It is not the simplest thing to learn as a beginner, and even if you think you have your head wrapped around the SQL world, let’s give you a better insight into what alter means in SQL.
In SQL, you have the alter table command.
Which is a DDL command that modifies the structure of an existing database table, it does so by adding, renaming, modifying, and even dropping columns and so forth.
You can use this to add, rename, and delete columns, or even just change the whole data type of the columns by simply using this command.
So, when we said that the dictionary definition of alter is different from SQL alter, we were right, to a certain extent. Alter is a command, which allows you to alter a table. It literally does just as it says, it alters it.
Of course, using the alter command is necessary, as altering tables in SQL is quite different from altering Microsoft Office products.
It is necessary, and thus it is necessary that anyone working with SQL is well-informed about how this all works.
Example Of An Alter Table
Imagine you have a table with information about people, customers, employees, whomever.
You would traditionally have information such as an ID number, first name, last name, address, and city, perhaps their zip code too. Now, perhaps you may decide you want to input their date of birth into the system as well, into this table.
To do so you would want to enter a command, ‘ALTER TABLE Persons.’ and ‘ADD DateOfBirth Date;’
This new column is a date type and will sustain a date, you note this as the type of data will specify what kind of data this column is to hold. This will input the D.O.B column into the table.
What Alter Allows You To Do
The alter command can allow any changes, realistically. As we said, it alters the table.
However, it does have specifics that are well known to many who work within computer science in offices.
Let’s look at a few examples of what the alter command can do.
Add Column Statement
If you work with SQL you are bound to need to add a column into an existing table at some point.
Of course, if you are a perfectionist you may be tempted to just create a whole new table or database again, but adding the column in is just so much easier.
You can add in single or multiple columns using the keyword ‘ADD’ when using alter in SQL.
However, using the ‘ADD’ keyword-only allows you to add another single column into the table, and if you need to add another four or five, you can save yourself from repeatedly having to use ‘ADD’ five times.
To add more than one column into a table you can use the syntax;
ALTER TABLE table_name
Add (column-Name1 column-definition,
Using this syntax for alter makes life easier, and you can get things done much faster. Alter is ready for whatever you need to do in your SQL statements.
Modifying Your Columns
Alter does not only allow you to add columns, it can allow you to do many other things too, such as modifying columns. Of course, such as with adding in columns, there is specific syntax to use for singular or multiple columns.
Knowing the syntax for these columns is important as it can save you much time in the long run, especially for large database changes over multiple columns.
To alter and modify a single column you would use the syntax ‘Alter Table table_name MODIFY column-name column definition.
However, to alter and modify multiple columns you would use the syntax ‘ALTER TABLE table_name MODIFY (column_Name1 column definition, column_Name2 column-definition, etc.’
While we often think about adding and modifying our databases and tables, we forget that there are occasions when we have to delete or drop, too.
If your database contained information about employees, and an employee left, you would need to alter the columns and drop some of them. The alter command for SQL can do this too. After all, deleting is altering the table.
How do you do this? Well, it is simple.
You need not delete the whole table or database, just use the magic keyword ‘DROP’ to delete columns from the database. It is super simple.
You can just input the following;
ALTER TABLE table_name DROP Column column_name.
Okay, so we know what an alter is now, don’t we? It is the command used to alter a table on a database in SQL. It’s super easy.
While the number of keywords and specifics can be overwhelming, the premise is as simple as it gets.
Really it is no different from learning how command-alt-delete works, or command-c, it is just a more in-depth and SQL-specific version of this in some ways.
We have covered some of the most commonly used commands for alter in SQL, however, there are more. You can rename columns, and more as well.
When first confronted with the use of SQL and the alter command, you might feel a little intimidated, as using so many keywords and learning them all can feel a little like coding and it kind of is, but it is much simpler, and it will keep database management so much more simple.