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Re: doubt about index


Am 23.06.2015 um 00:53 schrieb Roberto Spadim:
2015-06-22 19:47 GMT-03:00 Reindl Harald <h.reindl@xxxxxxxxxxxxx

    Am 23.06.2015 um 00:43 schrieb Roberto Spadim:

        hi guys, i`m with a doubt...
        when i have a primary key i know that's a unique key
        when i have a index with primary key + any other column, does
        consider that it's unique too?

    if it is defined as unique key yes

    what is "index with primary key + any other column"?

for example
create table x(
i int,
b int,
c int, d int , e int, ...
primary key(i),
key teste(b,i)

the test index is primary key (i column) + any other column (b,c,d,e,...)

these are two indexes

the second one is completly nosense as long your qquery is not in the form of "where b=x and i=y" and even "where i=y and b=x" won't be able to use it

 you have two keys in that case and the select uses one of them

yeap but some search algorithms use unique key/non unique key
information to improve search right?

which part of the documentation says that?

does it consider that any index that contains a unique index columns +
anyother column as "unique"

why should it?
it must not
just because they are not

        i`m thinking more about SELECT optimization

    how does it matter if a key is unique or not for select optimization?

select "where i=1" should return 0/1 rows (it's unique),
"where b=1" should return 0+ rows, but "where b=1 and i=1" should return
0/1 rows

it don't matter at all, these are two seperate indexes

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