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Null Values
In SQL, a cell with a NULL value indicates that the value is missing. A NULL value is very different from a zero value.
Constraints
When creating a table, we can define whether or not a field can or cannot be NULL, and that's a kind of constraint.
We will cover constraints in more detail soon; for now, let's focus on NULL values.
Assignment
We didn't force any constraints on our tables when we created them, and it has allowed for NULL entries to make their way into our table! Let's take a look at our transactions table to see what those NULL values look like.
Write a query to SELECT all fields on all records in the transactions table.
Observe
Notice that both the transaction_type and was_successful fields have NULL values in all 3 records in the table (nulls are represented by blank cells in our system). That's because we ran our migration in the previous exercise after the 3 records were created!
Tip
Use the * (wildcard) syntax to select all fields.