Join Bill Weinman for an in-depth discussion in this video Controlling column behaviors with constraints, part of SQL Essential Training.
…As you're defining your schema, you might want to…define specific rules and behaviors for some of your columns.…This is done using constraints.…For this lesson, we're using the in-memory database.…And, I'm going to start by creating a table,…so I'll type create table and call it test.…And we'll give it three columns, each of them text columns.…And we'll insert a row of data into it.…So here I'm just inserting data into the a and b columns.…The c column, I'm not inserting any data into…it so we would expect it to be a null.…
And we'll go ahead and take a look at the row.…And I'll press the go button.…And there's our result, we have one and two in…columns a and b and a null in column c.…It's exactly what we expect.…So column c has this null because we didn't specify a value for column c.…I can use a constraint called not null, in the definition of the column.…And then this behavior will no longer be allowed.…And so, this insert will generate an error.…If I press go here, you see, we have an integrity…constraint violation, test.c, that's the c column in the table test,…
- Understanding SQL terminology and syntax
- Creating new tables and records
- Inserting and updating data
- Writing basic SQL queries
- Sorting and filtering
- Accessing related tables with JOIN
- Working with strings
- Finding the numeric type of a value
- Using aggregate functions and transactions
- Updating a table with triggers
- Creating views
Skill Level Beginner
Q: For Mac OS X: When I try to start the Apache Web Server from the XAMPP control panel, it doesn't start, and when I open "localhost" in my web browser, I see a white screen that says "It Works!" instead of the XAMPP page.
sudo apachectl stop
Q: I'm on a Mac, and I get an error in SID that says "attempt to write a read only database." How can I fix this?
A: This usually means that the database folder does not have sufficient permissions for writing by the web user. This can happen if you create the SQL folder new, rather than copying it from the Exercise Files. Here's how to fix this:
- Open a Finder window and Navigate to /Applications/XAMPP/htdocs/SQL
- Control-click on the SQL folder and select "Get Info" from the context menu.
- Under "Sharing and Permissions" (you may need to open the disclosure triangle), in the "everyone" row, select "Read & Write."Then you can close the Info window.
- Now repeat the process for the three *.db files inside the folder.
1. SQL Quick Start
Understanding joins2m 23s
Dates and times1m 59s
10. Subselects and Views
11. A Simple CRUD Application
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