How multiple column b-tree index is organized

I want to understand better index organization. Imagine we have a table with 2 columns:

CREATE TABLE user( 
  name varchar(100)
 ,age int)

We would like to create an index:

CREATE INDEX IDX_MultiColIdx on user(name,age)

How would B-Tree index organization look like?

In case of one column, say, age, the organization is clear: every non-leaf node would contain a set of integer keys which would be used for a search. Which values contain nodes of our IDX_MultiColIdx B-Tree index?

Solution

Which values contains nodes of our IDX_MultiColIdx B-Tree index?

Values of name, age and the row pointer (RID/ROWID or clustered key, depending on the table organization), sorted lexicographically.

How exactly they will be stored, depends on the datatype and database system.

Usually, CHAR is stored right-padded with spaces up to its size, while VARCHAR is prepended with its length.

MyISAM and some other engines can use key compression: the matching parts of a set of keys are only stored once, and the other keys only store the differing parts, like this:

Hamblin
Hamblin, California
Hamblin (surname)
Hambling Baronets
Hambly
Hambly Arena    
Hambly Arena Fire
Hambo
Hambo Lama Itigelov
Hambok
Hambone

will be stored as:

Hamblin
[7], California
[7] (surname)
[7]g Baronets
Hambly
[6] Arena   
[6] Arena Fire
Hambo
[5] Lama Itigelov
[5]k
[5]ne

, where [x] means "take leading x characters from the previous key"