SQL syntax is a set of rules and guidelines used to write and execute SQL queries correctly.
- Uses specific keywords, clauses and operators to perform database operations.
- SQL keywords are generally written in uppercase for better readability.
Database Tables
A relational database consists of one or more tables. Each table contains records (rows) and fields (columns). For instance, consider a table named "employee":
SQL Statements
SQL statements are commands that perform specific actions on the database. Below are some of the most fundamental SQL statements:
SELECT Statement
The SELECT statement retrieves data from a database. It is one of the most commonly used SQL commands.
SELECT * FROM employee;INSERT INTO Statement
The INSERT INTO statement adds new rows to a table.
INSERT INTO employee (employee_id, first_name, last_name, birth_date, hire_date, department, position, salary)
VALUES (6, 'David', 'Wilson', '1992-03-18', '2020-09-15', 'Sales', 'Sales Manager', 68000);
UPDATE Statement
The UPDATE statement modifies existing records in a table.
UPDATE employee
SET salary = 80000
WHERE employee_id = 1;
DELETE Statement
The DELETE statement removes existing records from a table.
DELETE FROM employee
WHERE employee_id = 2;
ALTER TABLE Statement
The ALTER TABLE statement modifies an existing table.
ALTER TABLE employee
ADD COLUMN email VARCHAR(255);