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postgres=# CREATE DATABASE test_guru; | |
CREATE DATABASE | |
postgres=# CREATE TABLE categories ( | |
postgres(# id serial PRIMARY KEY, | |
postgres(# title varchar(40) | |
postgres(# ); | |
CREATE TABLE | |
postgres=# CREATE TABLE tests ( | |
postgres(# id serial PRIMARY KEY, | |
postgres(# title varchar(40), | |
postgres(# level int, | |
postgres(# category_id int | |
postgres(# ); | |
CREATE TABLE | |
postgres=# CREATE TABLE questions ( | |
postgres(# id serial PRIMARY KEY, | |
postgres(# body varchar(50), | |
postgres(# test_id int | |
postgres(# ); | |
CREATE TABLE | |
postgres=# INSERT INTO categories(title) VALUES | |
postgres-# ('Frontend'), | |
postgres-# ('Backend'), | |
postgres-# ('Fullstack'); | |
INSERT 0 3 | |
postgres=# SELECT* | |
postgres-# FROM categories; | |
id | title | |
----+----------- | |
1 | Frontend | |
2 | Backend | |
3 | Fullstack | |
(3 строки) | |
postgres=# INSERT INTO tests(title, level, category_id) VALUES | |
postgres-# ('Ruby', 2, 2), | |
postgres-# ('HTML', 1, 1), | |
postgres-# ('CSS', 2, 1), | |
postgres-# ('SQL', 3, 2), | |
postgres-# ('RoR', 3, 3); | |
INSERT 0 5 | |
postgres=# SELECT* | |
postgres-# FROM tests; | |
id | title | level | category_id | |
----+-------+-------+------------- | |
1 | Ruby | 2 | 2 | |
2 | HTML | 1 | 1 | |
3 | CSS | 2 | 1 | |
4 | SQL | 3 | 2 | |
5 | RoR | 3 | 3 | |
(5 строк) | |
postgres=# INSERT INTO questions(body, test_id) VALUES | |
postgres-# ('Why?', 2), | |
postgres-# ('Why not?', 1), | |
postgres-# ('Where?', 4), | |
postgres-# ('Who?', 2), | |
postgres-# ('How?', 3); | |
INSERT 0 5 | |
postgres=# SELECT* | |
postgres-# FROM questions; | |
id | body | test_id | |
----+----------+--------- | |
1 | Why? | 2 | |
2 | Why not? | 1 | |
3 | Where? | 4 | |
4 | Who? | 2 | |
5 | How? | 3 | |
(5 строк) | |
postgres=# SELECT* FROM tests WHERE level>1; | |
id | title | level | category_id | |
----+-------+-------+------------- | |
1 | Ruby | 2 | 2 | |
3 | CSS | 2 | 1 | |
4 | SQL | 3 | 2 | |
5 | RoR | 3 | 3 | |
(4 строки) | |
postgres=# SELECT* | |
postgres-# FROM questions | |
postgres-# WHERE test_id = 2; | |
id | body | test_id | |
----+------+--------- | |
1 | Why? | 2 | |
4 | Who? | 2 | |
(2 строки) | |
postgres=# UPDATE tests | |
postgres-# SET title = 'HAML', level = 3 | |
postgres-# WHERE title = 'HTML'; | |
UPDATE 1 | |
postgres=# SELECT* | |
postgres-# FROM tests; | |
id | title | level | category_id | |
----+-------+-------+------------- | |
1 | Ruby | 2 | 2 | |
3 | CSS | 2 | 1 | |
4 | SQL | 3 | 2 | |
5 | RoR | 3 | 3 | |
2 | HAML | 3 | 1 | |
(5 строк) | |
postgres=# DELETE | |
postgres-# FROM questions | |
postgres-# WHERE test_id = 4; | |
DELETE 1 | |
postgres=# SELECT* | |
postgres-# FROM questions; | |
id | body | test_id | |
----+----------+--------- | |
1 | Why? | 2 | |
2 | Why not? | 1 | |
4 | Who? | 2 | |
5 | How? | 3 | |
(4 строки) | |
postgres=# SELECT tests.title, categories.title | |
postgres-# FROM tests | |
postgres-# JOIN categories | |
postgres-# ON tests.category_id = categories.id; | |
title | title | |
-------+----------- | |
Ruby | Backend | |
CSS | Frontend | |
SQL | Backend | |
RoR | Fullstack | |
HAML | Frontend | |
(5 строк) | |
postgres=# SELECT questions.body, tests.title | |
postgres-# FROM questions | |
postgres-# JOIN tests | |
postgres-# ON questions.test_id = tests.id; | |
body | title | |
----------+------- | |
Why? | HAML | |
Why not? | Ruby | |
Who? | HAML | |
How? | CSS | |
(4 строки) |
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https://gist.github.com/Sandstorm750/8f7c3f058a97c903a8119c311223b377#file-sql2-L118
Здесь удобно использовать алиасы, чтобы было ясно где чей заголовок.