Very Computer

when creating a index unique in a table that accept nulls the unique
constraint doesn't work.

Example:
---
create table test_unique(i1 integer, i2 integer, unique(i1,i2);
insert into test_unique(1,null);
insert into test_unique(1,null);
insert into test_unique(1,null);
---
all "inserts" above insert sucefully.

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This is correct by spec.  NULLs are a special case.

From UNIQUE <table subquery) which unique constraints are defined
 against:
2) If there are no two rows in T such that the value of each column
   in one row is non-null and is equal to the value of the cor-
   responding column in the other row according to Subclause 8.2,
   "<comparison predicate>", then the result of the <unique predi-
   cate> is true; otherwise, the result of the <unique predicate>
   is false.

[This means that there will be no two rows such that the value
of each column in non-null and is equal to to the value in the
other since one of the columns is null]

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