SQL Server - index on a computed column?

Question

I\'m joining to a table dozens of different times, and every time, I join (or filter) based on the results of a SUBSTRING of one of the columns (it\'s a string, but left-pad

Answer 1

Add a calculated column to your table and create an index on this column.

ALTER TABLE MyTable
Add Column CodeHead As LEFT(Code,Len(Code)-4)

Then create an index on this.

CREATE INDEX CodeHeadIdx ON MyTable.CodeHead