Devon asks us to keep track of our operations aka missions as well. For the first implementation let us assume that a mission has one operative and an operative can participate in multiple missions. that’s what we call an 1 to many relationship.

  +------------+                 +----------+
  |            |1   active in   n|          |
  | operative  +-----------------+ missions |
  |            |                 |          |
  +------------+                 +----------+

Missions have an id, a code name like “Phantom Liberty”, an operative id and a total cost.

To say that the operative id is equivalent to the id in the operative column we use the FOREIGN KEY constraint.

So let’s create the new table in our database:

CREATE TABLE ki_missions 
(id INTEGER, code_name TEXT, operative_id INTEGER, total_cost DECIMAL(15,2), PRIMARY KEY(id), FOREIGN KEY (operative_id) REFERENCES operatives(id));
INSERT INTO ki_missions VALUES (1, "Knight of the Phoenix", 1, 6246382.43);
INSERT INTO ki_missions VALUES (2, "Deadly Maneuvers", 1, 4568893.53);

Our first join

SELECT ki_missions.code_name, ki_operatives.name FROM ki_missions LEFT JOIN ki_operatives ON ki_missions.operative_id = ki_operatives.id;

More on joins https://dsin.files.wordpress.com/2013/03/sqljoins_cheatsheet.png

Next chapter: SQL-Functions – SQL-Basics 3

The post SQL-Basics: Relations appeared first on Creatronix.

When you are really sure what you want to do:

SET SQL_SAFE_UPDATES = 0;

Now the dirty brown magic can begin!

Back to the SQL-Tutorial

The post SQL – the dark side appeared first on Creatronix.

In our example we have two tables which contain almost the same information:

CREATE TABLE installed_device (`id` int, `device` text, `info` text);
INSERT INTO installed_device (`id`, `device`, `info`) VALUES (1, "Device_1", "Works!"), (2, "Device_2", "Doesn't work!");
CREATE TABLE device (`id` int, `device_name` text);
INSERT INTO device (`id`, `device_name`) VALUES  (1, "Device_1"), (2, "Device_2");

installed_device

device

The goal is to replace the values in installed_device’s device column with the id from table device:

UPDATE installed_device SET device = (SELECT id FROM device WHERE device.device_name = installed_device.device);

The Result

The post SQL-Basics – Subqueries: Update column with values from another column appeared first on Creatronix.