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By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0. 2335789 fiddles created (27474 in the last week).

CREATE TABLE #Students( [Name] varchar(50), [Surname] varchar(50), [Period] int, [Sport] int, [History] int, [English] int, [Geography] int)
 hidden batch(es)


INSERT INTO #Students([Name],[Surname],[Period],[Sport],[History],[English],[Geography]) VALUES ('Luke','Green',1,30,20,23,NULL), ('Mary','Brown',1,17,15,NULL,30), ('John','Red',1,18,NULL,21,30), ('Walter','White',1,22,20,5,30), ('Luke','Green',2,30,20,23,NULL), ('Mary','Brown',2,NULL,15,17,30), ('John','Red',2,18,NULL,11,30), ('Walter','White',2,2,32,1,30), ('Luke','Green',3,20,15,15,12), ('Mary','Brown',3,0,3,NULL,4), ('John','Red',3,18,40,21,30), ('Walter','White',3,17,19,15,30), ('John','Red',3,NULL,23,23,30);
13 rows affected
 hidden batch(es)


SELECT * FROM #Students
Name Surname Period Sport History English Geography
Luke Green 1 30 20 23
Mary Brown 1 17 15 30
John Red 1 18 21 30
Walter White 1 22 20 5 30
Luke Green 2 30 20 23
Mary Brown 2 15 17 30
John Red 2 18 11 30
Walter White 2 2 32 1 30
Luke Green 3 20 15 15 12
Mary Brown 3 0 3 4
John Red 3 18 40 21 30
Walter White 3 17 19 15 30
John Red 3 23 23 30
 hidden batch(es)


SELECT COUNT([Surname]) FROM #Students
(No column name)
13
 hidden batch(es)


SELECT COUNT(DISTINCT [Surname]) FROM #Students
(No column name)
4
 hidden batch(es)