SQL Server B-Tree: Index Seek
dbo.Users — clustered index on Id (identity)
SELECT
*
FROM
dbo.Users
WHERE
Id = 12345;
page reads:
1
2
3
4
Root
Level 3
Intermediate
Level 2
Intermediate
Level 1
Leaf · data
Level 0
Root page 1:100
Id 1 → 1:200
Id 500,001 → 1:201
Id 1,000,001 → 1:202
Id 1 → 1:200
Intermediate page 1:200
Id 1 → 1:410
Id 8,001 → 1:411
Id 24,001 → 1:412
⋯
Id 8,001 → 1:411
Intermediate page 1:201
Id 500,001 → …
…
Intermediate page 1:202
Id 1,000,001 → …
…
⋯
Intermediate page 1:410
Id 1 → …
…
Intermediate page 1:411
Id 8,001 → 1:300
Id 12,001 → 1:301
Id 16,001 → 1:302
⋯
Id 12,001 → 1:301
Intermediate page 1:412
Id 24,001 → …
…
⋯
Page 1:300
Id 8,001
Id 9,500
Id 11,000
⋯
Page 1:301
Id 12,001
Id 12,345
Id 12,900
Id 13,800
Id 14,750
Id 15,200
Page 1:302
Id 16,001
Id 18,500
Id 21,000
⋯
⋯