ADD: database initialization sql file

+CREATE DATABASE secondhand-noti-bot;
+
+CREATE TABLE user
+(
+    id INT(10) NULL AUTO_INCREMENT
+);
+
+CREATE TABLE keyword
+(
+    id      INT     NOT NULL,
+    keyword VARCHAR NULL
+);
+
+CREATE TABLE user_keyword
+(
+    id         INT NOT NULL AUTO_INCREMENT,
+    user_id    INT NOT NULL,
+    keyword_id INT NOT NULL,
+    FOREIGN KEY (user_id) REFERENCES user (id) ON DELETE CASCADE,
+    FOREIGN KEY (keyword_id) REFERENCES keyword (id) ON DELETE CASCADE,
+);
+
+CREATE TABLE item
+(
+    id            INT      NOT NULL,
+    keyword_id    INT      NOT NULL,
+    platform      VARCHAR  NOT NULL,
+    name          VARCHAR  NOT NULL,
+    price         INT      NOT NULL,
+    thumbnail_url VARCHAR  NULL,
+    item_url      VARCHAR  NOT NULL,
+    extra_info    TEXT     NULL,
+    created_at    DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE TABLE item_check
+(
+    id      INT NOT NULL AUTO_INCREMENT,
+    item_id INT NULL,
+    user_id INT NULL,
+    FOREIGN KEY (item_id) REFERENCES item (id) ON DELETE CASCADE,
+    FOREIGN KEY (user_id) REFERENCES user (id) ON DELETE CASCADE
+);