The NULL value represents a lack of value. It is separate and distinct from zero or a zero-length string.
- [Instructor] Null is a special state … for a result with no value. … This is necessary because it's often important … to distinguish between a zero value or an empty string … or a non-value result. … This lesson, we're going to be using the test database again … and we're going to be using the test table … that we've been working with for the past few lessons. … In the last two movies, … we created this table for learning about inserting … and deleting rows, and it looks like this. … Notice the word null in the result in the A column here … on the first record … and also in this row with all nulls in it. … Null is a special state in SQL. … It's not really a value. … It's the lack of a value, … so you can not test for it as you would a normal value … with the equals sign because it has no value, … so if I say, if I add a where clause here … and say where a is equal to null, … you'll notice that I don't get any results. … This is because there is no row where a is equal to null … because null has no value …
This course was created by Bill Weinman. We are pleased to offer this training in our library.
- How databases are organized
- Selecting rows and columns
- Creating new tables
- Inserting and updating data
- Sorting and filtering
- Accessing related tables with JOIN
- Working with strings
- Understanding numeric types
- Using aggregate functions and transactions
- Automating data with triggers
- Creating views
- Using CRUD functions
Skill Level Beginner
2. SQL Overview
3. Fundamental Concepts
7. Dates and Times
Dates and times2m 6s
11. Views and Subselects
12. A Simple CRUD Application
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