Difference between Select Unique and Select Distinct

When to Use Distinct

Duplication Dilemma in Merged Data

Imagine you're combining data from multiple tables. Here's where our hero SELECT DISTINCT shines, ensuring only unique rows prevail, especially when dealing with union or join operations:

SELECT DISTINCT table_one.column_a, table_two.column_b
FROM table_one
INNER JOIN table_two ON table_one.id = table_two.id;
# "No repeats, please" - DISTINCT, probably


Maintaining Uniqueness in Data

In the SQL world, unique constraints are the equivalent of bouncers at a nightclub. They enforce data integrity, making sure no two entries get too friendly in a specific column or set of columns:

CREATE TABLE cocktail_party (
    guest_id INT,
    CONSTRAINT no_gatecrashers UNIQUE (guest_id)
);
# Always apply for an invite beforehand


A primary key, likewise, acts as a unique identifier spotlit in a dimly lit data club.

Distinct Use Cases

Demonstrating the use and effects of SELECT DISTINCT can be enlightening, especially for those new to SQL. It's like taking someone on a guided tour of an amusement park.

Error-Free SQL Journey

The road to SQL mastery is fraught with potholes, but it doesn't have to be. Using the correct syntax, like SELECT DISTINCT, will smooth the ride. The signboard saying SELECT UNIQUE may be misleading; always follow the DISTINCT highway.

Delving into Distinct

Perfect Timing: When to go Distinct

Knowing when to deploy DISTINCT is like knowing when to take a pawn off the chessboard. For instance, creating insightful reports or dashboards often requires distinct counts:

SELECT COUNT(DISTINCT username)
FROM users;
# Counting people, not their doppelgängers.
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Filtering Out Clones

When dealing with a table that treats unique constraints like optional dress codes, SELECT DISTINCT becomes essential to filter out duplicates in a sea of potential clones.

Distinct with Union of Tables

In SQL's grand orchestra, combining UNION and DISTINCT produces a harmonious melody of unique result sets:

SELECT DISTINCT fruit_name
FROM (
    SELECT fruit_name FROM fruit_basket_1
    UNION ALL
    SELECT fruit_name FROM fruit_basket_2
) AS fruit_concerto;
# Never too much of a good thing, but no repeats either!


Uniqueness: A Design Essential

Maintaining data uniqueness isn't just a design objective; it's a requirement. Leveraging unique constraints during table creation facilitates this directive from day zero.

Syntax Correctness: A Must-Have

The difference between gibberish and eloquence in SQL sometimes hangs on accurate syntax usage. Using SELECT DISTINCT ensures your code is not only standard-compliant but also significantly more readable to other developers.