Delete your data

1. Delete your data

In the last two lessons you've learned how to both create & edit tables in your database. Now you will learn how to delete records and tables in your database.

2. DROP, TRUNCATE, DELETE

The extreme case of removing tables from your database involves dropping them. The DROP TABLE command removes the table you specify from your database. If, you wanted to keep the table structure but remove all of the records in your table the command your would use is TRUNCATE TABLE followed by the name of the table whose records you would like to clear. Finally, if you wanted to remove only selected records from a table you would use the DELETE FROM command followed by the table name from which to delete the records from and use a WHERE statement to specify the conditions that determine which records you would like to delete. Let's work through an example of the last approach.

3. DELETE inactive customers

In this scenario, you need to remove all inactive customers from your database. This means you need to delete all records from the customer table WHERE the active column is equal to FALSE. This translates into the SQL statement shown on the slide.

4. DELETE using a subquery

Just like with UPDATE you can delete records based on conditions identified in other tables by leveraging subqueries. Mirroring the subquery UPDATE example in the last video you can see a very similar approach. Here you start with the DELETE FROM command and limit it to cases where address ids belong to those found in your subquery. In this case the subquery returns the address ids from the address table of customers that reside in the city of Woodridge. The only difference is the DELETE syntax.

5. Let's DELETE some records!

Remember that just like with UPDATE, you need be extra cautious with the DELETE, TRUNCATE & DROP commands when working with a real-world database. With that in mind, it's time to practice what you've learned.

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This exercise is part of the course

Applying SQL to Real-World Problems

IntermediateSkill Level

4.9+

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You will review some of the most commonly used SQL commands to ensure you are prepared to tackle both real-world problems as well as every exercise covered in this course.

Exercise 1: Essential SQL Exercise 2: Review the essentials Exercise 3: Practice the essentials Exercise 4: Transforming your results Exercise 5: Transform numeric & strings Exercise 6: Extract what you need Exercise 7: Working with aggregate functions Exercise 8: Aggregating finances Exercise 9: Aggregating strings Exercise 10: Which tables?

How do you find the data you need in your database in order to answer real-world business questions? Here you will learn how to use system tables to explore your database. You will use these tables to create a new tool that contains a list of all tables and columns in your database. Finally, you will create an Entity Relationship Diagram (ERD) which will help you connect multiple tables.

Exercise 1: Find the right table Exercise 2: LIMITing your search Exercise 3: Which table to use?Exercise 4: What tables are in your database?Exercise 5: Determine the monthly income Exercise 6: Join the correct tables Exercise 7: What columns are in your database?Exercise 8: A VIEW of all your columns Exercise 9: Testing out your new VIEW Exercise 10: The average length of films by category Exercise 11: Complex joins Exercise 12: Build the entity relationship diagram Exercise 13: Which films are most frequently rented?

Working with SQL to solve real-world problems will oftentimes require you to do more than retrieve the data you need, oftentimes you will need to manage the data in your database. This includes creating data, updating it and, when necessary, deleting it.

Exercise 1: Store your data Exercise 2: Storing new data Exercise 3: Using existing data Exercise 4: TABLE vs VIEW Exercise 5: Update your data Exercise 6: What should you modify?Exercise 7: Update the price of rentals Exercise 8: Updated based on other tables Exercise 9: Delete your data

Current Exercise

Exercise 10: Deleting all table data Exercise 11: Delete selected records Exercise 12: A family friendly video store

How do you ensure that the SQL scripts you write will be easy to understand for anyone who needs to read them? This chapter will cover approaches you can leverage to ensure that your code clearly conveys your intent, is readable by others and follows best practices.

Exercise 1: Convey your intent Exercise 2: How to convey our intent Exercise 3: Clarify the intent of this query Exercise 4: Fix this query - intent Exercise 5: Write readable code Exercise 6: How to make code easier to read Exercise 7: Make this query easier to read - Part I Exercise 8: Make this query easier to read - Part II Exercise 9: Avoid common mistakes Exercise 10: What are the don'ts of writing SQL code?Exercise 11: Apply best practices to your code Exercise 12: Recap