How to make a field unique??

[COMP]

Hi i am trying to make the field project reference unique, so that users do not enter in twice. Now it is not the primary key so any ideas as to how?? i have tried to change the settings on the index. Index(Ok No duplicates) but it doesnt allow me to. I have checked that there isnt any duplicates so not sure to why that is happening.

Any ideas??

 

[KenHigg]

If all else fails copy the structure to a new table, make the change to not allow duplicates then append the existing data.

 

[gemma-the-husky]

create an index based on the unique field and set it to no duplicates

if that fails then you DO have duplicate values that are preventing the index.

try doing a groupby query to find the instances of values with mutiple usages.

 

[boblarson]

And an empty string (instead of a null) can potentially cause the problem. I would do what Ken suggested.