CREATE TABLE user_workspaces (
 user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
 workspace_id INTEGER NOT NULL REFERENCES workspaces(id) ON DELETE CASCADE,
 PRIMARY KEY (user_id, workspace_id)
);
CREATE TABLE user_pads (
 user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
 pad_id INTEGER NOT NULL REFERENCES pads(id) ON DELETE CASCADE,
 PRIMARY KEY (user_id, pad_id)
);