SQL Data Types
Overview
In this lesson, we'll cover the importance of specifying datatypes, and the different types of data you can store in a SQLite database.
Objectives
Describe data typing and how it allows for operations to be performed with predictable results
List four different types of data you can store in a SQLite database.
Define three specific SQLite database types: Text, Integer, and Real.
Why Do Data Types Matter?
We've learned that when we create a table, we need to include a name for it as well as define at least one column. We define columns in a CREATE statement by including a name and a datatype to let SQLite know the kind of data we will be storing there. The practice of explicitly declaring a type is known as "typing."
Why is it important that we use typing in our database? Simply put, typing allows us to exercise some level of control over our data. Typing not only informs our database of the kind of data we plan to store in a column but it also restricts it. For instance, look at the age column below in our cats table. What do we mean by age? What if we had this:
name
breed
age
Maru
Scottish Fold
3
Hannah
Tabby
two
Lil' Bub
American Shorthair
5.5
Did we intend age to be represented as a whole-number, a word, or a decimal? If we asked you to add up the ages of all the cats you could simply convert the 'two' to 2 in your head, but your database can't do that. It doesn't have that ability because the logic involved in converting a word into a number would be dense and inefficient. What about different languages? What about different spellings? Capitalization, typos, or different hyphenation conventions? These are just some reasons this might start to get crazy. In other words, because databases are designed to store large amounts of data, they are very concerned with storing, accessing, and acting upon that data as efficiently and normally as possible.
Typing gives us the ability to perform all kinds of operations with predictable results. For instance, the ability to perform Math operations like SUM - i.e. summing integers - doesn't just depend on everything being an integer of some sort but would also expect it. If you tried, for example, to SUM all of the cats in the above table, SQLite would actually attempt to convert, or cast, their type to something it can SUM. It would try to convert anything it can to an INTEGER and ignore alpha characters. This can lead to real problems. Without typing, our data might get complicated and messy, and it would be difficult to ask the database questions about large sets of data.
We're going to adhere strictly to only storing data that fits with the datatype we have given to a particular column.
Datatypes
Different database systems also have different datatypes available, which are important and useful to know whenever you are dealing with those systems. SQLite is a good starting point to learn about datatypes because it only has four basic categories of datatypes; they are:
Let's explore each category in more detail.
TEXT
Any alphanumeric characters which we want to represent as plain text. The body of this paragraph is text. Your name is text. Your email address is a piece of text. Your height, weight, and age, however, are probably not.
INTEGER
Anything we want to represent as a whole number. If it's a number and contains no letter or special characters or decimal points then we should store it as an integer. If we use it to perform math or create a comparison between two different rows in our database, then we definitely want to store it as an integer. If it's just a number, it's generally not a bad idea to store it as an integer. You might never add two house address numbers together, but you might want to sort them numerically. For example in the preceding case, you might want to get the biggest number and not the longest piece of text.
REAL
Anything that's a plain old decimal like 1.3 or 2.25. SQLite will store decimals up to 15 characters long. You can store 1.2345678912345 or 1234.5678912345, but 1.23456789123456789 would only store 1.2345678912345. In other database systems this is called 'double precision.'
With these three types in hand, we are going to be able to work our way through the next several topics, and this whole typing concept is going to quickly become second nature for you.
BLOB
You may encounter the BLOB datatype while you're Googling or doing any further reading on SQLite. For now, we will not use BLOB. It is generally used for holding binary data.
Bonus: Note on SQLite
To increase its compatibility with other database engines (E.G. mySQL or PostgreSQL), SQLite allows the programmer to use other common datatypes outside of the four mentioned above. This is why we are referring to TEXT INTEGER REAL BLOB as datatype "categories". All other common datatypes are lumped into one of the four existing datatypes recognized by SQLite.
For example, INT is a common datatype used outside of SQLite. SQLite won't complain if you define a column as an INT datatype. It will simply lump it into the INTEGER category and store it as such.
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