SQL: Select, Insert, Update, and Delete
Table of Contents
Introduction
SQL can be used to access data within a database. This chapter describes how SQL can be used to find, insert and update data in a database.
Select statement
Select statement can be used to access data in a database. It is a very low risk command; it just reads data and does not change the database in any way. This means, if we make a mistake with our select commands, we cannot damage the database.
SELECT column1, column2, … FROM table_name;
To get all columns from a table
SELECT * FROM table_name;
Insert statement
Insert can be used to add a new record into a table.
INSERT INTO table_name (column1, column2, column3, ...) VALUES (value1, value2, value3, ...);
In this command, value1 will go into column1, value2 will go into columne2, etc...
Update statement
Update modifies an existing record in the database. It (sorta) combines select and insert. It selects a row in the database and then inserts new values.
UPDATE table_name SET column1 = value1, column2 = value2, ...
WHERE condition;
Update statements require a WHERE clause to identify row(s) to update. We discuss WHERE in Chapter 5.
Delete statements
Deletes an existing record in the database.
DELETE FROM table_name WHERE condition;
Delete also require a WHERE clause to identify row(s) to update. We discuss WHERE in Chapter 5.