create table user (
 user_id             bigint not null auto_increment primary key,
 user_name           varchar(255)
);

create table client (
 client_id           bigint not null auto_increment primary key,
 client_name         varchar(255),
 client_hourly_rate  float
);

create table project (
 project_id          bigint not null auto_increment primary key,
 project_name        varchar(255),
 project_client_id   bigint references client.client_id,
 project_hourly_rate float
);

create table invoice (
 invoice_id          bigint not null auto_increment primary key,
 invoice_foreign_id  varchar(32),
 invoice_time        datetime
);

create table iv (
 iv_id          bigint not null auto_increment primary key,
 iv_user_id     bigint references user.user_id,
 iv_project_id  bigint references project.project_id,
 iv_starttime   datetime,
 iv_duration    int,
 iv_workdone    varchar(255),
 iv_hourly_rate float,
 iv_billable    tinyint not null default 1,
 iv_invoice_id  bigint references invoice.invoice_id
);