I have a mysql table that stores relationships. Items can be related to another item in one direction, or both items can be related to each other.

I want to return all items related to my primary item - but I also want to check to see if the related item has a 'reverse relationship' to the current item and show this as a boolean

 |--------------|---------------|
 |    SKU       |  related_SKU  |
 |--------------|---------------|
 | 0001         |  0099         |
 | 0002         |  0099         |
 | 0099         |  0001         |
 |--------------|---------------|

If I want to get all relationships for SKU=0001

SELECT related_SKU from relationships where SKU='0001'

returns

 |--------------|
 | related_SKU  |
 |--------------|
 | 0099         |
 |--------------|

but what I want is

 |--------------|---------------|
 | related_SKU  |   reciprocal  |
 |--------------|---------------|
 | 0099         |      1        |
 |--------------|---------------|

or

 SELECT related_SKU from relationships where SKU='0002'

 |--------------|---------------|
 | related_SKU  |   reciprocal  |
 |--------------|---------------|
 | 0099         |      0        |
 |--------------|---------------|

What's the best way to do this?