transactions + schema migrations

Author: swagfinger

01.SQL.md

@@ -93,6 +93,8 @@
 
 [15. Materialized Views](#15-materialized-views)
 
+[16. Transactions](#16-transactions)
+
 ---
 ###### <div style="text-align:right">[table of contents](#table-of-contents)</div>
 ## 1. Basics
@@ -1509,6 +1511,8 @@ syntax: CREATE OR REPLACE VIEW _ AS
 	DROP VIEW recent_posts;
 ```
 ---
+###### <div style="text-align:right">[table of contents](#table-of-contents)</div>
+
 ## 15. Materialized views
 Query that gets executed only at very specific times, but the results are saved and
 can be referenced without rerunning the query.
@@ -1546,3 +1550,32 @@ modifying any data in materialized view (SQL statement), will require us to refr
 ```SQL 
 REFRESH MATERIALIZED VIEW  weekly_likes;
 ```
+
+---
+###### <div style="text-align:right">[table of contents](#table-of-contents)</div>
+
+## 16. Transactions
+locks to updates to ensure execution succeeds in order.
+Transactions ensure all execute successfully or none execute successfully (roll-back).
+when opening up a transaction, database makes an 'isolated workspace'. any SQL statements run are isolated until transaction ends with COMMIT.
+
+##### Opening a transaction / complete a transaction
+```SQL
+BEGIN; --executing starts a transaction
+
+---some sql
+
+COMMIT; -- to finish transaction
+```
+
+##### closing a transaction
+If an error occurs after BEGIN call, manually run ROLLBACK needs to be executed.
+if a crash occurs, postgres rolls back transaction 
+
+##### Simulating a crash / recover from error
+(postgress-> dashboard -> server activity -> *(close connections that have 'CONN'))
+if you check database, postgres did an auto rollback.
+
+```SQL
+ROLLBACK; -- revert
+```

02.database_design.md

@@ -9,6 +9,7 @@
 + [Mention system](#mention-system)
 + [Hashtag system](#hashtag-system)
 + [follower system](#follower-system)
++ [creating instagram database](#creating-instagram-database)
 
 ---  
 
@@ -488,3 +489,128 @@ Table followers {
 }
 ```
 
+---
+
+###### <div style="text-align:right">[table of contents](#table-of-contents)</div>
+
+## creating instagram database
+
+1. servers -> localhost -> databases -> (right-click create)
+2. open query tool by right clicking on specific database
+
+###### users table
+```SQL
+CREATE TABLE users (
+	id SERIAL PRIMARY KEY,
+	created_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP,
+	updated_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP,
+	username VARCHAR(30) NOT NULL,	
+	bio VARCHAR(400),
+	avatar VARCHAR(200),
+	phone VARCHAR(25),
+	email VARCHAR(40),
+	password VARCHAR(50),
+	status VARCHAR(15),
+	CHECK(COALESCE(phone, email) IS NOT NULL)
+);
+```
+
+###### posts table
+```SQL
+CREATE TABLE posts (
+	id SERIAL PRIMARY KEY,
+	created_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP,
+	updated_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP,
+	url VARCHAR(200) NOT NULL,
+	caption VARCHAR(240),
+	lat REAL CHECK(lat IS NULL OR (lat >= -90 AND lat <= 90)), 
+	lng REAL CHECK(lng IS NULL OR (lng >= -180 AND lng <= 180)),
+	user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE
+);
+```
+
+###### comments table
+```SQL
+CREATE TABLE comments (
+	id SERIAL PRIMARY KEY,
+	created_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP,
+	updated_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP,
+	contents VARCHAR(240) NOT NULL,
+	user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+	post_id INTEGER NOT NULL REFERENCES posts(id) ON DELETE CASCADE
+);
+```
+
+###### likes table
+```SQL
+CREATE TABLE likes (
+	id SERIAL PRIMARY KEY,
+	created_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP,
+	user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+	post_id INTEGER REFERENCES posts(id) ON DELETE CASCADE,
+	comment_id INTEGER REFERENCES comments(id) ON DELETE CASCADE,
+	CHECK(
+		COALESCE((post_id)::BOOLEAN::INTEGER, 0)
+		+
+		COALESCE((comment_id)::BOOLEAN::INTEGER, 0)
+		= 1
+	),
+	UNIQUE(user_id, post_id, comment_id)
+);
+```
+
+###### photo_tags 
+```SQL
+CREATE TABLE photo_tags (
+	id SERIAL PRIMARY KEY,
+	created_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP,
+	updated_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP,
+	user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+	post_id INTEGER NOT NULL REFERENCES posts(id) ON DELETE CASCADE,
+	x INTEGER NOT NULL,
+	y INTEGER NOT NULL,
+	UNIQUE(user_id, post_id)
+);
+```
+
+###### caption_tags
+```SQL
+CREATE TABLE caption_tags (
+	id SERIAL PRIMARY KEY,
+	created_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP,
+	user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+	post_id INTEGER NOT NULL REFERENCES posts(id) ON DELETE CASCADE,
+	UNIQUE(user_id, post_id)
+);
+```
+
+###### hashtags
+```SQL
+CREATE TABLE hashtags (
+	id SERIAL PRIMARY KEY,
+	created_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP,
+	title VARCHAR(20) NOT NULL UNIQUE
+);
+```
+
+###### hashtags_post
+```SQL
+CREATE TABLE hashtags_posts (
+	id SERIAL PRIMARY KEY,
+	hashtag_id INTEGER NOT NULL REFERENCES hashtags(id) ON DELETE CASCADE,
+	post_id INTEGER NOT NULL REFERENCES posts(id) ON DELETE CASCADE,
+	UNIQUE(hashtag_id, post_id)
+);
+```
+
+###### followers
+```SQL
+CREATE TABLE followers (
+	id SERIAL PRIMARY KEY,
+	created_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP,
+	leader_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+	follower_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+	UNIQUE(leader_id, follower_id)
+);
+```
+