index concept
PK IX_Last
ID LastName ID LastName
1 L 1 L
2 L 2 L
3 T 5 L
4 T 7 L
5 L 9 L
6 T 10 L
7 L 3 T
8 T 4 T
9 L 6 T
10 L 8 T
where LastName = “L" will use IX_Last
PK IX_Last
ID LastName ID LastName
1 L 1 L
2 L 2 L
3 T 5 L
4 T 7 L
5 L 9 L
6 T 10 L
7 L 3 T
8 T 4 T
9 L 6 T
10 L 8 T
where LastName = “L" will use IX_Last