CREATE TABLE tenant_plan_subscriptions (
    id         BIGSERIAL PRIMARY KEY,
    tenant_id  BIGINT NOT NULL REFERENCES tenants(id),
    plan_id    BIGINT NOT NULL REFERENCES plans(id),
    start_at   TIMESTAMPTZ NOT NULL,
    end_at     TIMESTAMPTZ NOT NULL,
    status     VARCHAR(20) NOT NULL DEFAULT 'active',
    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    deleted_at TIMESTAMPTZ
);
CREATE UNIQUE INDEX idx_tenant_plan_active ON tenant_plan_subscriptions(tenant_id) WHERE status = 'active' AND deleted_at IS NULL;