that would mean Every row in foo for column f1 has to be unique and Every row in foo for column f2 has to be unique
Say for example: create table test1 ( a int, b int ) ; create unique index idx_t1_a on test1(a) ; create unique index idx_t1_b on test1(b) ; insert into test1 values (1,1) ; -- OK insert into test1 values (1,2) ; -- FAIL insert into test1 values (2,2) ; -- OK insert into test1 values (2,1) ; -- FAIL This is because the each record is composed to two unique columns, and the uniqueness is broken down to each column, rather than the record as a whole. In case when you are creating the index as: create unique index idx_t1_ab on test1(a, b) ; insert into test1 values (1,1) ; -- OK insert into test1 values (1,2) ; -- OK insert into test1 values (2,2) ; -- OK insert into test1 values (2,1) ; -- OK This is because, each combination of column a and column b is unique in it's entirety. hth, dotyet On Fri, Feb 22, 2008 at 6:53 AM, Naz Gassiep <[EMAIL PROTECTED]> wrote: > If you have an index like this: > > CREATE UNIQUE INDEX foo ON tablename (f1, f2); > > Is there any value in having independent indicies on f1 and f2 as well > or are they unnecessary? > > Thanks > - Naz. > > ---------------------------(end of broadcast)--------------------------- > TIP 5: don't forget to increase your free space map settings >
