[Edit] SQL not-equal-to

content/sql/concepts/operators/terms/not-equal-to/not-equal-to.md

@@ -5,38 +5,168 @@ Subjects:
   - 'Computer Science'
   - 'Data Science'
 Tags:
-  - 'Operators'
   - 'Database'
   - 'MySQL'
+  - 'Operators'
   - 'PostgreSQL'
-  - 'SQLite'
 CatalogContent:
   - 'learn-sql'
   - 'paths/data-science'
 ---
 
-In SQL, the **`NOT EQUAL TO`** operator is used to compare two values. It returns true if the values are not equal and false if they are equal. The operator can be represented in two ways: `<>` or `!=`.
+The **`NOT EQUAL TO`** operator in SQL is a comparison operator used to compare two values. It returns `true` if the values aren't equal and `false` if they are equal. The operator can be represented in two ways: `<>` or `!=`.
+
+It is commonly used in the [`WHERE`](https://www.codecademy.com/resources/docs/sql/commands/where) clause to exclude specific records from the result set. The `NOT EQUAL TO` operator is essential for creating precise queries that filter out unwanted data.
 
 ## Syntax
 
-```pseudo
--- Using the <> operator
-SELECT column1, column2, ...
-FROM table_name
+The syntax for the `NOT EQUAL TO` operator in SQL is:
+
+```sql
 WHERE column_name <> value;
+```
+
+Or alternatively:
 
--- Using the != operator
-SELECT column1, column2, ...
-FROM table_name
+```sql
 WHERE column_name != value;
 ```
 
-## Example
+The `column_name` represents the column being evaluated, and `value` is the specific criterion being compared.
+
+> **Note:** Although both `<>` and `!=` symbols can be used for the `NOT EQUAL TO` operator, `<>` follows the ISO standard while `!=` does not. It is generally recommended to use `<>` for better compatibility.
+
+## Example 1: Using `NOT EQUAL TO` with Text Values
+
+Here's a sample `customers` table with location data:
+
+```sql
+CREATE TABLE customers (
+  ID INT,
+  Name VARCHAR(100),
+  City VARCHAR(100),
+  State CHAR(2)
+);
+
+INSERT INTO customers VALUES
+(1, 'Smith', 'New York', 'NY'),
+(2, 'Johnson', 'Chicago', 'IL'),
+(3, 'Martinez', 'Los Angeles', 'CA'),
+(4, 'Brown', 'New York', 'NY'),
+(5, 'Wilson', 'Miami', 'FL'),
+(6, 'Thompson', 'Dallas', 'TX');
+```
+
+This example demonstrates how to use the `NOT EQUAL TO` operator to exclude specific text values from results:
+
+```sql
+SELECT *
+FROM customers
+WHERE city <> 'New York';
+```
+
+This query returns all the records from the customers table where the city is not equal to 'New York':
+
+```shell
+ID  Name        City         State
+2   Johnson     Chicago      IL
+3   Martinez    Los Angeles  CA
+5   Wilson      Miami        FL
+6   Thompson    Dallas       TX
+```
+
+## Example 2: Using `NOT EQUAL TO` with Numeric Values
+
+For this example, let's work with a `products` table containing various electronics items:
+
+```sql
+CREATE TABLE products (
+  product_id INT,
+  product_name VARCHAR(100),
+  price DECIMAL(10,2)
+);
+
+INSERT INTO products VALUES
+(1, 'Keyboard', 29.99),
+(2, 'Monitor', 149.99),
+(3, 'Standard Mouse', 19.99),
+(4, 'Mouse', 14.99),
+(5, 'Headphones', 59.99),
+(6, 'USB Drive', 19.99);
+```
+
+This example shows how to filter numeric data using the `NOT EQUAL TO` operator:
+
+```sql
+SELECT product_name, price
+FROM products
+WHERE price != 19.99;
+```
+
+This query retrieves all products where the price is not $19.99:
+
+```shell
+product_name    price
+Keyboard        29.99
+Monitor         149.99
+Mouse           14.99
+Headphones      59.99
+```
+
+## Example 3: Combining `NOT EQUAL TO` with Multiple Conditions
+
+To demonstrate more complex filtering, consider this company `employees` database table:
+
+```sql
+CREATE TABLE employees (
+  emp_id INT,
+  name VARCHAR(100),
+  department VARCHAR(100),
+  salary DECIMAL(10,2)
+);
+
+INSERT INTO employees VALUES
+(101, 'Johnson', 'Sales', 45000),
+(102, 'Davis', 'Sales', 52000),
+(103, 'Williams', 'Marketing', 65000),
+(104, 'Miller', 'Sales', 48000),
+(105, 'Rodriguez', 'IT', 70000),
+(106, 'Garcia', 'HR', 47000),
+(107, 'Jones', 'Sales', 55000),
+(108, 'Taylor', 'Finance', 61000),
+(109, 'Wilson', 'HR', 42000),
+(110, 'Clark', 'IT', 72000);
+```
 
-The given query will select all employees who are not in the `Sales` department using the `NOT EQUAL TO` operator.
+This example demonstrates how to use the `NOT EQUAL TO` operator with multiple conditions using logical operators:
 
 ```sql
 SELECT *
 FROM employees
-WHERE department <> 'Sales';
+WHERE department <> 'Sales'
+AND salary > 50000;
 ```
+
+This query retrieves all employees who do not work in the 'Sales' department and have a salary greater than $50,000:
+
+```shell
+emp_id  name          department    salary
+103     Williams      Marketing     65000
+105     Rodriguez     IT            70000
+108     Taylor        Finance       61000
+110     Clark         IT            72000
+```
+
+## Frequently Asked Questions
+
+### 1. What is the difference between `<>` and `!=` in SQL?
+
+Both `<>` and `!=` are `NOT EQUAL TO` operators in SQL and function identically. However, `<>` follows the ISO SQL standard, while `!=` is not part of the standard. For maximum compatibility across different database systems, it's recommended to use `<>`.
+
+### 2. Is the `NOT EQUAL TO` operator case-sensitive for text comparisons?
+
+The case sensitivity of the `NOT EQUAL TO` operator depends on the database system and its collation settings. In most databases like [MySQL](https://www.codecademy.com/resources/docs/mysql) with default settings, string comparisons are case-insensitive. However, in databases like [PostgreSQL](https://www.codecademy.com/resources/docs/postgresql), they are typically case-sensitive by default.
+
+### 3. Can I use the `NOT EQUAL TO` operator with `NULL` values?
+
+No, comparing any value with `NULL` using `NOT EQUAL TO` will not work as expected. `NULL` represents an unknown value, so neither `column <> NULL` nor `column = NULL` will return the expected results. Instead, use [`IS NULL`](https://www.codecademy.com/resources/docs/sql/operators/is-null) or [`IS NOT NULL`](https://www.codecademy.com/resources/docs/sql/operators/is-not-null) operators.