title: Having a string array field as an index, good or bad?
body: <p>My gut feel is that setting a string (with array elements) field as an index on a table will be bad for performance (where the bulk of the operations done on a table are inserts and updates - the table holds transactional data and its current size is approximately 20 mil records).</p>
  
  <p>The string extends a type with 4 array elements, where all of them aren’t always populated.  I need to justify why not to set this field as one of the indexes.  I’ve tried searching for answers, reading Kimberley Tripps blog, going through best practises re indexes on MSDN (which only mentions indexes are best on numerics first, then string fields), etc.  But none of these mention indexing the table on a field that is of an array type.  What reasons can I give to justify not indexing on the string-array field.  And if my gut feel  is totally wrong and indexes work well on array fields, why so?</p>