feat(backend-db): sql schema containing tables and relationships

This commit adds a schema.sql that initialises tables and relationships for managing user data.

Closes #39

Author: Sampath-1984

backend/db/schema.sql

@@ -0,0 +1,32 @@
+CREATE TABLE user_info (
+	id BIGSERIAL NOT NULL PRIMARY KEY,
+	name VARCHAR(50) NOT NULL,
+	age SMALLINT NOT NULL CHECK(age > 0),
+	year SMALLINT NOT NULL CHECK(year IN (1,2,3,4)),
+	branch VARCHAR(50) NOT NULL CHECK(branch IN ('CSE','ECE','MECH','SM','BDES')),
+	bio VARCHAR(500),
+	image VARCHAR(200),
+	public_key VARCHAR(500) NOT NULL
+);
+
+CREATE TABLE tags_table (
+	id BIGSERIAL NOT NULL PRIMARY KEY,
+	name VARCHAR(50) NOT NULL
+);
+
+CREATE TABLE tags_user_table (
+	tag_id BIGINT NOT NULL REFERENCES tags_table(id),
+	user_id BIGINT NOT NULL REFERENCES user_info(id)
+);
+
+CREATE TABLE choices_for_chooser (
+	chooser_id BIGINT NOT NULL REFERENCES user_info(id),
+	chosen_id BIGINT REFERENCES user_info(id),
+	UNIQUE (chooser_id)
+);
+
+CREATE TABLE choices_for_chosen (
+	chosen_id BIGINT NOT NULL REFERENCES user_info(id),
+	chooser_id BIGINT REFERENCES user_info(id),
+	UNIQUE (chosen_id)
+);