MySQL 8.0

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create table testTable (unique_id int, uid int);
insert into testTable values (123487, 1000);
insert into testTable values (123488, null);
insert into testTable values (123489, null);
insert into testTable values (123490, null);
select * from testTable;


unique_id
uid


123487
1000

123488
null

123489
null

123490
null


 SELECT max(uid) FROM testTable;


max(uid)


1000


select ROW_NUMBER() OVER (order by unique_id) rn  from testTable
 where uid is null;


rn


1

2

3


CREATE PROCEDURE uid_update()
    
    BEGIN
    
     DECLARE Done_c INT;
     DECLARE v_min_id INT;
     declare number_plus int;
     declare v_cur int;
     
     DECLARE curs CURSOR FOR 
     select ROW_NUMBER() OVER (order by unique_id) rn  
     from testTable
     where uid is null;
     
     DECLARE CONTINUE HANDLER FOR NOT FOUND SET Done_c = 1;
    
     SELECT max(uid) INTO number_plus FROM testTable;
     
     OPEN curs;
    
      SET Done_c = 0;
      REPEAT
           FETCH curs INTO v_cur;
    
           select min(unique_id) into v_min_id 
           from testTable 
           where uid is null;
           
           update testTable
           set uid = number_plus + v_cur
           where uid is null
           and unique_id = v_min_id ;
           
           commit;
           
           UNTIL Done_c END REPEAT;
    
      CLOSE curs;
     
END
call uid_update;
select * from testTable;


unique_id
uid


123487
1000

123488
1001

123489
1002

123490
1003