UPDATE and DELETE Statements

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From the course by IBM

Databases and SQL for Data Science

42 ratings

IBM

Databases and SQL for Data Science

42 ratings

Course 4 of 4 in the Specialization Introduction to Data Science

SQL is a powerful language which is used for communicating with databases. Before you step into the field of data science, it is vitally important that you set yourself apart by mastering the foundations of SQL. The purpose of this course is to introduce relational database concepts and help you learn and apply knowledge of the SQL language. Learners will also practice building and running SQL queries hands-on using a cloud-based environment as well as learn how to access databases from Jupyter notebooks using Python. If you choose to take this course and earn the Coursera course certificate, you will also earn an IBM digital badge upon successful completion of the course.

From the lesson

Week 1 - Introduction to Databases and Basic SQL

In Week 1 you will be introduced to databases. You will create a database instance on the cloud. You will learn some of the basic SQL statements. You will also write and practice basic SQL hands-on on a live database.

CREATE Table Statement2:51

SELECT Statement3:36

INSERT Statement2:36

UPDATE and DELETE Statements3:12

Meet the Instructors

Rav Ahuja
Data Science Program Manager
IBM Cognitive Class
Hima Vasudevan
Data Scientist
IBM Digital Business Group

Hello and welcome to the UPDATE statement and the DELETE statement.

In this video, we will learn about altering and

deleting data in a relational database table.

At the end of this lesson,

you will be able to identify the syntax of the UPDATE statement and

DELETE statement and explain the importance of the WHERE clause in these statements.

After a table is created and populated with data,

the data in a table can be altered with the UPDATE statement.

The UPDATE statement is one of the data manipulation language or DML statements.

DML statements are used to read and modify data.

Based on the author entity example,

we created the table using the entity name

Author and the entity attributes as the columns of the table.

Rows were added to the Author table to populate the table.

Sometime later, you want to alter the data in the table.

To alter or modify the data in the Author table,

we use the UPDATE statement.

The syntax of the UPDATE statement looks like this,

UPDATE [TableName] SET [ColumnName] = [Value] ]> <WHERE [Condition] >.

In the statement, TableName identifies the table.

The ColumnName identifies the column value to be changed,

as specified in the <WHERE [Condition] >.

Let's look at an example.

In this example, you want to update the FIRSTNAME and LASTNAME of

the author with AUTHOR_ID A2 from Rav Ahuja to Lakshmi Katta.

In this example, to see the UPDATE statement in action,

we start by selecting all rows from the author table to see the values.

To change the first name and last name to Lakshmi Katta where the AUTHOR_ID = A2,

enter the UPDATE statement as follows.

UPDATE AUTHOR SET LAST NAME = KATTA,

FIRST NAME = LAKSHMI WHERE AUTHOR_ID = A2.

Now, to see the result of the update,

select all rows again from the Author table and you will see that in row

to the name changed from Rav Ahuja to Lakshmi Katta.

Note that if you do not specify the WHERE clause,

all the rows in the table will be updated.

In this example, without specifying the WHERE clause all rows in

the table would have changed the first and last names to Lakshmi Katta.

Sometime later, there might be a need to remove one or more rows from a table.

The rows are removed with the DELETE statement.

The DELETE statement is one of

the data manipulation language statements used to read and modify data.

The syntax of the DELETE statement looks like this,

DELETE FROM [TABLEName] <WHERE [Condition] >.

The rows to be removed are specified in the WHERE condition.

Based on the author entity example,

we want to delete the rows for AUTHOR_ID A2 and A3.

Let's look at an example.

DELETE FROM AUTHOR WHERE AUTHOR_ID IN ('A2','A3').

Note that if you do not specify the WHERE clause,

all the rows in the table will be removed.

Now you can identify the syntax of the UPDATE statement and

DELETE statement and explain the importance of the WHERE clause in these statements.

Thanks for watching this video.

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