The execution plan for this query appears to be making a very bad choice (of course I know it is not):

```
SELECT TOP 1 E_PER_ID FROM E WHERE E_CUS_ID = 1912 AND E_TYPE = 'R' ORDER BY E_ID DESC

```

The two relevant indexes are:

```
CREATE NONCLUSTERED INDEX IX_EMAIL_2 ON EMAIL
(E_CUS_ID ASC, E_DATE_SENT ASC)
WITH (FILLFACTOR = 95)

CREATE NONCLUSTERED INDEX IX_EMAIL_3 ON EMAIL
(E_ID ASC, E_TYPE ASC, E_CUS_ID ASC)
INCLUDE (E_PER_ID)
WITH (FILLFACTOR = 95)

```

The query plan is choosing IX\_EMAIL\_2.

It appears IX\_EMAIL\_3 is covering and IX\_EMAIL\_2 is clearly not.

Is this simply b/c the E\_CUS\_ID key column is first in IX\_EMAIL\_2?

I wasn't aware a completely covering index would be ignored by the engine in favor of an index w/ only one of the needed columns but that column was first in the index.

NOTE: This table has 121M records so I can't do much testing to see if I'm right without waiting many hours.