Sql is null and = null

Ground rules for NULL in SQL

NULL: A maverick in SQL universe

In the realm of SQL, NULL signifies an absence of value. It's a state indicating "unknown value", "no value given", or "value doesn’t apply". Since it represents a lack of value, any standard comparison like =, <>, or < is a no-no with NULL.

NULL: The game changer in SQL operations

Indulge NULL in any SQL operation, and voila! The outcome is deemed unknown. This holds true for arithmetic operations, string mashups, and comparisons with other values. Here's a lil' sampler to bring out this peculiarity:

Incorrect - Expecting no results just like my dating app 😟

SELECT 'Match Found' WHERE NULL = NULL;
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Correct - Finally, a match! 😌

SELECT 'Match Found' WHERE NULL IS NULL;
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Avoid these RED FLAGS with NULL

When using NULL with aggregate functions, proceed with caution my friend:

• COUNT(column_name) – It's a ‘no’ on counting rows if column_name is NULL.
• SUM and AVG – They ‘shun’ NULL values, which could sneakily alter the overall value.

The curious case of NULL in SQL

NULL: Schrodinger's cat of SQL

In SQL queries, treat NULL like Schrodinger's cat—it doesn't exist or not exist, until put under the observant eye of the correct predicate like IS NULL or IS NOT NULL.

NULL’s got conditions in SQL

When NULL enters the realm of comparisons: It conjures up unknown results:

--NULL doesn't play 'Not Equal to' hence, no show in WHERE clause (probably off attending a wizardry convention 🎩✨)
SELECT 'This won’t appear' WHERE NULL <> NULL;

--NULL combined with any value, even itself, doesn't end in a happy union (😭💔)
SELECT 'Neither will this' WHERE NULL = 1;
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Acing the NULL game in SQL

• Use COALESCE or ISNULL to substitute NULLs with a ‘plan B’.
• Employ IS NOT NULL as your go-to to ensure that a column wears a non-NULL hat.

NULL’s DAY OUT: IS NULL and = NULL

Conditional queries in SQL: Time for an encounter with NULL

Make your peace with how to look for NULL when setting up conditional SQL queries. Using IS NULL in a condition is like deploying your special search dog to look for no-value sneaks:

-- Fetch rows that are Batman (i.e., hiding ‘description’ just like BatCave)
SELECT * FROM products WHERE description IS NULL;
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NULL: A special guest star in OUTER JOINs

This is NULL’s star turn. It makes a guest appearance in OUTER JOIN operations, when NULL can be the missing person in a column of a table sans a match:

-- Find customers who are on a shopping detox
SELECT customers.name, orders.order_id
FROM customers
LEFT JOIN orders ON customers.customer_id = orders.customer_id
WHERE orders.order_id IS NULL;
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NULL and Indexing: A SQL thriller

Mind your step! Indexes pretty much ghost NULL values, which could sneakily alter query performance:

-- An index on 'email' will not help. It’s busy friendzoning this query
SELECT * FROM users WHERE email IS NULL;
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