indexes on two varchar columns

[ilyalyu]

I have read that if you create index on two columns ("index (col1, col2)") the columns are concatenated. But if I have 2 varchar columns and I have the following rows:
'abc', 'd'
'ab', 'cd'
does it mean that I have index 'abcd' for both of this rows. If so the usefulnes of such index will be very limited.

[r937]

no, it means you have an index with the values --

'abc', 'd'
'ab', 'cd'