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PostgreSQL: Insert Data into a Table

PostgreSQL: Insert Data into a Table

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M B A R K
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Before inserting data, it's essential to understand the structure of the table you want to populate. For demonstration purposes, let's consider a simple "users" table with the following schema:

CREATE TABLE users (
    user_id SERIAL PRIMARY KEY,
    first_name VARCHAR(50),
    last_name VARCHAR(50),
    age INT
);

The user_id column is an auto-incrementing primary key, while first_name, last_name, and age columns hold user information.

Inserting a Single Row

To insert a single row into the "users" table, you can use the INSERT INTO statement. Here's an example:

INSERT INTO users (first_name, last_name, age)
VALUES ('John', 'Doe', 30);

In this example, we specify the column names in the parentheses after INSERT INTO, followed by the VALUES keyword, and then the corresponding data for each column.

Inserting Multiple Rows

If you want to insert multiple rows in one go, you can use the following syntax:

INSERT INTO users (first_name, last_name, age)
VALUES
    ('Jane', 'Smith', 25),
    ('Michael', 'Johnson', 40),
    ('Emily', 'Brown', 22);

Here, we provide multiple sets of data within the VALUES clause, separated by commas.

Copying Data from CSV

PostgreSQL allows you to bulk-insert data from a CSV (Comma-Separated Values) file. Let's assume you have a file named "user_data.csv" with the same structure as the "users" table. You can use the following command:

COPY users (first_name, last_name, age) FROM 'path/to/user_data.csv' DELIMITER ',' CSV HEADER;

Replace 'path/to/user_data.csv' with the actual path to your CSV file. The DELIMITER ',' specifies that the values are separated by commas, and CSV HEADER indicates that the first row contains the column headers.

Inserting Data from a Query

You can also insert data into a table using the results of a SELECT query. This technique is handy when you want to duplicate data from one table to another or transform existing data. Here's an example:

INSERT INTO users (first_name, last_name, age)
SELECT first_name, last_name, age FROM temporary_users WHERE age > 25;

This query selects records from the "temporary_users" table where the age is greater than 25 and inserts the results into the "users" table.

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