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What are the AND and OR clauses in PostgreSQL?

Saad Qadeer

Overview

In SQL, we use the AND and OR clauses to write and combine multiple conditions. They are a crucial part of SQL when defining conditions to separate/filter the data we need from the remaining raw dataset.

These clauses are used along with standard SQL clauses, such as the WHERE clause.

Code

Using the code below, we can set up a sample data table.

-- Initialize a table named states
CREATE TABLE states(
    first_name varchar(255),
    state varchar(255),
    city varchar(255)
);

-- Populate the table with sample data
INSERT INTO 
    -- Table name
    states
        -- Column names
        (first_name, state, city)
    
    -- Sample Data
    VALUES
        ('Drake', 'California', 'Los Angeles'),
        ('Josh', 'California', 'Los Angeles'),
        ('Megan', 'Texas', 'Houston'),
        ('Audrey', 'Texas', 'Dallas'),
        ('Walter', 'Florida', 'Miami');

-- Diplay the table
SELECT * 
FROM states;
Generate sample data

When we run the code snippet above, we can see that we've successfully been able to declare and populate a table by the name of states.

The AND clause

SELECT *
FROM states
WHERE state = 'California' AND first_name = 'Drake';
AND clause

We've used the AND clause to filter the data based on two conditions. The code above will return a table of people named Drake living in the state of California.

The AND clause will only display records if all the stated conditions are successfully met.

The OR clause

SELECT *
FROM states
WHERE state = 'Texas' OR state = 'Florida';
OR clause

The code written above returns records matching either of the stated conditions. People currently living in the state of California or the state of Texas will show up in the output table.

Unlike the AND clause, the OR clause will display records that successfully meet any of the conditions stated.

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