mysql implements the operation of setting multiple primary keys

CREATE TABLE `user` (
 `user_id` INT(11) NOT NULL,
 `user_name` VARCHAR(255) NOT NULL,
 `password` VARCHAR(255) NOT NULL,
 `phone` VARCHAR(255) NOT NULL,
 PRIMARY KEY (`user_id`)
)
COMMENT = 'User table'
COLLATE='utf8_general_ci'
ENGINE=InnoDB;

CREATE TABLE `admin` (
 `user_id` INT(11) NOT NULL,
 `user_name` VARCHAR(255) NOT NULL,
 `password` VARCHAR(255) NOT NULL,
 `phone` VARCHAR(255) NOT NULL,
 PRIMARY KEY (`user_id`)
)
COMMENT = 'Administrator table'
COLLATE='utf8_general_ci'
ENGINE=InnoDB;

CREATE TABLE `sequence` (
 `seq_name` VARCHAR(50) NOT NULL,
 `current_val` INT(11) NOT NULL,
 `increment_val` INT(11) NOT NULL DEFAULT '1',
 PRIMARY KEY (`seq_name`)
)
COMMENT = 'Sequence List'
COLLATE='utf8_general_ci'
ENGINE=InnoDB;

INSERT INTO sequence VALUES ('seq_test', '0', '1');

delimiter #
create function currval(v_seq_name VARCHAR(50)) 
returns integer(11) 
begin
 declare value integer;
 set value = 0;
 select current_val into value from sequence where seq_name = v_seq_name;
 return value;
end;

select currval('seq_test');

delimiter #
create function nextval (v_seq_name VARCHAR(50)) returns integer(11) 
begin
 update sequence set current_val = current_val + increment_val where seq_name = v_seq_name;
 return currval(v_seq_name);
end;

select nextval('seq_test');

<insert id="addUser" parameterType="User">
  <selectKey keyProperty="userId" resultType="int" order="BEFORE">
   select nextval('seq_test');
  </selectKey>
  insert into user(user_id,user_name,password,phone) values
  (#{userId},#{userName, jdbcType=VARCHAR},#{password, jdbcType=VARCHAR}, #{phone, jdbcType=VARCHAR})
 </insert>

<insert id="addAdmin" parameterType="Admin">
  <selectKey keyProperty="userId" resultType="int" order="BEFORE">
   select nextval('seq_test');
  </selectKey>
  insert into admin(user_id,user_name,password,phone) values
  (#{userId},#{userName, jdbcType=VARCHAR},#{password, jdbcType=VARCHAR}, #{phone, jdbcType=VARCHAR})
 </insert>