6 - How to Select Data from a TABLE

Selecting Data from a Table

• To query all data from a table, use SELECT * FROM table_name
• To select specific columns, replace * with the column names, e.g., 

SELECT first_name , last_name 
FROM employees;

• You can change the order of the columns in the query

Using the WHERE Clause

• The WHERE clause is used to filter data based on specific criteria
• Example:

SELECT * FROM employees WHERE employee_ID = 1

• You can use various operators, such as =, >, >=, <, <=, !=

Examples of Using the WHERE Clause

Find all employees with a specific first name: 

SELECT * FROM employees WHERE first_name = 'SpongeBob'

Find all employees with an hourly pay greater than or equal to $15: 

SELECT * FROM employees WHERE hourly_pay >= 15

Find all employees with a hire date less than or equal to a specific date: 

SELECT * FROM employees WHERE hire_date <= '2023-01-03'

Using the NOT Operator

• The NOT operator is used to find data that does not match a specific criteria
• Example: SELECT * FROM employees WHERE employee_ID != 1
• You can use the IS NOT NULL or IS NULL operators to check for null values

Best Practices

• Use specific columns instead of * to reduce the amount of data returned
• Use the WHERE clause to filter data based on specific criteria
• Use various operators and the NOT operator to refine your queries