From the documentation of SHOW INDEX (found by @diEcho):
SHOW INDEX returns the following fields:
Non_unique -- 0 if the index cannot contain duplicates, 1 if it can.
Column_name -- The column name.
Try:
SHOW INDEXES
FROM $tablename
WHERE Column_name='$field'
AND NOT Non_unique
Note that this assumes that there is no UNIQUE index that spans multiple columns. If there can be, then you might want to exclude these with a subquery.
Also note disabled indexes also show in this query (the possibility of disabled indexes is mentioned in the documentation on the Comment
column). There doesn't seem to be a column reflecting this, so you might need to parse the Comment
column if you have disabled indexes.
There's no need to compare Non_unique
to a number - MySQL uses 0 and 1 for booleans anyways