How to use conditions to filter data in SQL

The usage of WHERE in SQL requires specific code examples

SQL (Structured Query Language) is a standardized language used to manage relational database management systems (RDBMS) . In SQL, the WHERE clause is used to filter the data returned by the SELECT statement. Through the WHERE clause, we can select the required data rows based on specific conditions.

The general syntax of the WHERE clause is as follows:

SELECT column1, column2, ... FROM table_name WHERE condition; In the above syntax, column1, column2, ... are the columns you want to select, table_name is the table you want to select data from, condition is the condition for filtering data.

Some common examples will be given below to illustrate the usage of WHERE.

Simple equal operator ( = ): SELECT * FROM customers WHERE city = 'New York'; The above code will select all locations from the customers table New York customers.

Not equal to operator ( ): SELECT * FROM employees WHERE department <> 'HR'; The above code will be from the employees table Select all employees whose department is not HR.

Greater than operator ( > ): SELECT * FROM products WHERE price > 100; The above code will select the price greater than 100 from the products table of all products.

Less than operator ( ): SELECT * FROM orders WHERE order_date The above code will select the order date earlier from the orders table All orders placed on January 1, 2021.

Greater than or equal to operator ( >= ): SELECT * FROM customers WHERE age >= 18; The above code will select the age from the customers table All customers aged 18 and above.

Less than or equal to operator ( ): SELECT * FROM employees WHERE hire_date The above code will select onboarding from the employees table All employees with a date before or equal to January 1, 2019.

BETWEEN Operator: SELECT * FROM products WHERE price BETWEEN 50 AND 100; The above code will select all products with a price between 50 and 100 from the products table.

LIKE and wildcard operators: SELECT * FROM customers WHERE last_name LIKE 'Sm%'; The above code will select all customers whose last name starts with "Sm" from the customers table. The wildcard character % represents any character.

IN Operator: SELECT * FROM employees WHERE department IN ('HR', 'Sales'); The above code will select all employees whose department is HR or Sales from the employees table.

The above are sample codes for some common WHERE clauses. Through these examples, you can better understand the usage of WHERE clause in SQL queries. According to actual needs, you can write WHERE clauses based on different conditions to obtain the required data rows.

How to use conditions to filter data in SQL

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