MySQL 8.0

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Create table Student (student_id int);
insert into Student 
with recursive cte 
as (select 1 id union all select id+1 from cte where id < 500) 
select id from cte;
delete 
from Student
where student_id in 
(
with recursive cte 
as (select 1 id union all select id+1 from cte where id < 100)
select cast(rand() * 500 as unsigned) from cte
)
select count(*) from Student


count(*)


421


SELECT n
FROM (
        SELECT /* 1000*n1+ */ 100*n2+10*n3+n4+1 n
        FROM 
               /* (
                SELECT 0 n1 UNION 
                SELECT 1 UNION 
                SELECT 2 UNION 
                SELECT 3 UNION 
                SELECT 4 UNION 
                SELECT 5 UNION 
                SELECT 6 UNION 
                SELECT 7 UNION 
                SELECT 8 UNION 
                SELECT 9 
                ) n1,
              */  (
                SELECT 0 n2 UNION 
                SELECT 1 UNION 
                SELECT 2 UNION 
                SELECT 3 UNION 
                SELECT 4 UNION 
                SELECT 5 UNION 
                SELECT 6 UNION 
                SELECT 7 UNION 
                SELECT 8 UNION 
                SELECT 9
                ) n2,
                (
                SELECT 0 n3 UNION 
                SELECT 1 UNION 
                SELECT 2 UNION 
                SELECT 3 UNION 
                SELECT 4 UNION 
                SELECT 5 UNION 
                SELECT 6 UNION 
                SELECT 7 UNION 
                SELECT 8 UNION 
                SELECT 9
                ) n3,
                (
                SELECT 0 n4 UNION 
                SELECT 1 UNION 
                SELECT 2 UNION 
                SELECT 3 UNION 
                SELECT 4 UNION 
                SELECT 5 UNION 
                SELECT 6 UNION 
                SELECT 7 UNION 
                SELECT 8 UNION 
                SELECT 9
                ) n4
        HAVING n < (
                    SELECT MAX(student_id)
                    FROM Student
                  )
     ) numbers
LEFT JOIN Student ON student_id = n
WHERE student_id IS NULL


n


11

421

31

341

361

381

202

12

312

412

132

472

3

303

403

13

23

423

104

204

114

124

34

144

244

254

454

264

74

194

394

5

205

405

415

425

45

465

206

416

26

226

426

436

246

356

266

76

376

486

296

217

417

137

257

357

267

367

187

308

438

248

58

268

188

198

419

129

449

279

379

89

289

310

140

240

390

300