Updating PostgreSQL Tables: INSERT, UPDATE and DELETE

This blog teaches you how to use the INSERT, UPDATE and DELETE statements to modify data in PostgreSQL tables using SQL commands.

1. Introduction

In this blog, you will learn how to use the INSERT, UPDATE and DELETE statements to modify data in PostgreSQL tables. These statements are part of the SQL language, which is used to interact with relational databases. By using these statements, you can add new rows, change existing values, or remove rows from your tables.

Why is this important? Because modifying data is a common and essential task when working with databases. You may need to insert new data from various sources, update data to reflect changes in the real world, or delete data that is no longer relevant or accurate. By mastering these statements, you will be able to manipulate your data efficiently and effectively.

What do you need to follow this tutorial? You need to have PostgreSQL installed on your system and a basic understanding of how to create and query tables. You also need to have a text editor or an IDE that supports SQL syntax highlighting, such as Visual Studio Code or Sublime Text.

Are you ready to learn how to modify data in PostgreSQL tables? Let’s get started!

2. Creating a Sample Table

Before you can use the INSERT, UPDATE and DELETE statements to modify data in PostgreSQL tables, you need to have a table to work with. In this section, you will learn how to create a sample table using the CREATE TABLE statement.

The CREATE TABLE statement allows you to define the name, columns, data types, constraints, and indexes of a new table. The basic syntax of the statement is as follows:

CREATE TABLE table_name (
    column1 data_type constraints,
    column2 data_type constraints,
    ...
    columnN data_type constraints
);

For example, suppose you want to create a table called customers that stores information about the customers of an online store. The table has four columns: id, name, email, and phone. The id column is the primary key, which means it uniquely identifies each row in the table. The name and email columns are not null, which means they cannot be empty. The phone column is optional, so it can be null. The data type of each column is integer, text, text, and text, respectively. The following SQL command creates the customers table:

CREATE TABLE customers (
    id integer PRIMARY KEY,
    name text NOT NULL,
    email text NOT NULL,
    phone text
);

To execute the command, you can use a tool such as pgAdmin or psql to connect to your PostgreSQL database and run the command in the query editor. Alternatively, you can use a programming language such as Python or Java to connect to your database and execute the command programmatically.

After creating the table, you can use the \d command in psql or the Properties tab in pgAdmin to view the details of the table. You should see something like this:

\d customers
              Table "public.customers"
 Column |  Type   | Collation | Nullable | Default 
--------+---------+-----------+----------+---------
 id     | integer |           | not null | 
 name   | text    |           | not null | 
 email  | text    |           | not null | 
 phone  | text    |           |          | 
Indexes:
    "customers_pkey" PRIMARY KEY, btree (id)

Congratulations! You have successfully created a sample table in PostgreSQL. In the next section, you will learn how to insert data into the table using the INSERT statement.

3. Inserting Data into a Table

Now that you have created a sample table called customers, you can use the INSERT statement to add new rows of data to the table. The INSERT statement allows you to specify the values for each column of the new row, or use the default values if any. The basic syntax of the statement is as follows:

INSERT INTO table_name (column1, column2, ..., columnN)
VALUES (value1, value2, ..., valueN);

For example, suppose you want to insert a new row into the customers table with the following values: id = 1, name = ‘Alice’, email = ‘alice@example.com’, and phone = ‘123-456-7890’. The following SQL command inserts the new row:

INSERT INTO customers (id, name, email, phone)
VALUES (1, 'Alice', 'alice@example.com', '123-456-7890');

You can also omit the column names and provide the values in the same order as the columns in the table. For example, the following command is equivalent to the previous one:

INSERT INTO customers
VALUES (1, 'Alice', 'alice@example.com', '123-456-7890');

However, this is not recommended, as it can lead to errors if the order or number of columns in the table changes. It is better to always specify the column names explicitly.

You can also insert multiple rows at once by using a comma-separated list of values. For example, the following command inserts three rows into the customers table:

INSERT INTO customers (id, name, email, phone)
VALUES (2, 'Bob', 'bob@example.com', '234-567-8901'),
       (3, 'Charlie', 'charlie@example.com', NULL),
       (4, 'David', 'david@example.com', '345-678-9012');

Note that the phone value for the third row is NULL, which means it is unknown or missing. This is allowed, as the phone column is not defined as NOT NULL in the table.

To verify that the data has been inserted correctly, you can use the SELECT statement to query the table. For example, the following command selects all the rows and columns from the customers table:

SELECT * FROM customers;

You should see something like this:

Congratulations! You have successfully inserted data into a PostgreSQL table using the INSERT statement. In the next section, you will learn how to update data in a table using the UPDATE statement.

4. Updating Data in a Table

Sometimes, you may need to change the values of some columns in a PostgreSQL table to reflect new or updated information. For example, you may want to change the name, email, or phone number of a customer in the customers table. To do this, you can use the UPDATE statement, which allows you to modify one or more columns of one or more rows in a table. The basic syntax of the statement is as follows:

UPDATE table_name
SET column1 = value1, column2 = value2, ..., columnN = valueN
WHERE condition;

The SET clause specifies the columns and the new values that you want to assign to them. The WHERE clause specifies the condition that identifies which rows to update. If you omit the WHERE clause, all the rows in the table will be updated, which is usually not what you want.

For example, suppose you want to update the name and email columns of the row with id = 1 in the customers table. You want to change the name from ‘Alice’ to ‘Alex’ and the email from ‘alice@example.com’ to ‘alex@example.com’. The following SQL command updates the row:

UPDATE customers
SET name = 'Alex', email = 'alex@example.com'
WHERE id = 1;

To verify that the data has been updated correctly, you can use the SELECT statement to query the table. For example, the following command selects the row with id = 1 from the customers table:

SELECT * FROM customers
WHERE id = 1;

You should see something like this:

Congratulations! You have successfully updated data in a PostgreSQL table using the UPDATE statement. In the next section, you will learn how to delete data from a table using the DELETE statement.

5. Deleting Data from a Table

Sometimes, you may need to remove some rows of data from a PostgreSQL table that are no longer needed or relevant. For example, you may want to delete the customer with id = 4 from the customers table, as they have requested to unsubscribe from your online store. To do this, you can use the DELETE statement, which allows you to delete one or more rows from a table. The basic syntax of the statement is as follows:

DELETE FROM table_name
WHERE condition;

The WHERE clause specifies the condition that identifies which rows to delete. If you omit the WHERE clause, all the rows in the table will be deleted, which is usually not what you want.

For example, suppose you want to delete the row with id = 4 from the customers table. The following SQL command deletes the row:

DELETE FROM customers
WHERE id = 4;

To verify that the data has been deleted correctly, you can use the SELECT statement to query the table. For example, the following command selects all the rows and columns from the customers table:

SELECT * FROM customers;

You should see something like this:

Congratulations! You have successfully deleted data from a PostgreSQL table using the DELETE statement. In the next and final section, you will learn how to summarize the main points of the tutorial and provide some additional resources for further learning.

6. Conclusion

In this blog, you have learned how to use the INSERT, UPDATE and DELETE statements to modify data in PostgreSQL tables. These statements are essential for manipulating data in relational databases, as they allow you to add, change, or remove rows from your tables. You have also learned how to use the CREATE TABLE and SELECT statements to create and query tables, as well as how to use the WHERE clause to filter the rows that you want to modify or retrieve.

By following this tutorial, you have gained the following skills:

• How to create a sample table using the CREATE TABLE statement.
• How to insert data into a table using the INSERT statement.
• How to update data in a table using the UPDATE statement.
• How to delete data from a table using the DELETE statement.
• How to query data from a table using the SELECT statement.
• How to use the WHERE clause to specify the condition for modifying or retrieving data.

We hope you have enjoyed this tutorial and found it useful for your learning.

Thank you for reading this blog and happy learning!