Re: [MonetDB-users] how to write function like oracle nvl()?

But i expect one tuple, then what can i do? On Tue, Jul 13, 2010 at 3:57 PM, Stefan Manegold wrote:

On Tue, Jul 13, 2010 at 03:26:37PM +0800, Mike Jason wrote:

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Thanks for you reply, it helps in some cases, but I think there are more complicated cases, such as:

create table t2 (id int, name varchar(100)); insert into t2 values (1, 'abc'); insert into t2 values (2, 'xyz'); select nvl((select name from t2 where name='ab'), 'xxx');

I hope the result has one tuple:

'xxx'

but it returns 0 tuple.

I'd expect 0 tuple (i.e., an empty result0 as the result of the subquery, and thus the first argument to nvl() is empty, and not NULL ...

Stefan

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On Tue, Jul 13, 2010 at 2:21 PM, Stefan Manegold

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Hi Mike,

here are a couple of alternatives (IMHO in plain standard SQL ;-)):

with

======== create table t (a int, b string); insert into t values (1,null); insert into t values (null,'2 2'); select * from t;

select a, case when b is null then 'n.a.' else b end from t;

select case when a is null then 0 else a end, b from t;

create function nvl_string(e1 string, e2 string) returns string begin case when e1 is null then return e2; else return e1; end case; end;

create function nvl_int(e1 int, e2 int) returns int begin if e1 is null then return e2; else return e1; end if; end;

select a, nvl_string(b,'n.a.') from t;

select nvl_int(a,0), b from t;

drop table t; drop function nvl_string; drop function nvl_int; ========

I get

======== [ 1 ] [ 1 ] % sys.t, sys.t # table_name % a, b # name % int, clob # type % 1, 3 # length [ 1, NULL ] [ NULL, "2 2" ] % sys.t, sys. # table_name % a, ifthenelse_isnull_isnull_b # name % int, clob # type % 1, 4 # length [ 1, "n.a." ] [ NULL, "2 2" ] % sys., sys.t # table_name % ifthenelse_isnull_isnull_a, b # name % int, clob # type % 1, 3 # length [ 1, NULL ] [ 0, "2 2" ] % sys.t, sys. # table_name % a, nvl_string_b # name % int, clob # type % 1, 4 # length [ 1, "n.a." ] [ NULL, "2 2" ] % sys., sys.t # table_name % nvl_int_a, b # name % int, clob # type % 1, 3 # length [ 1, NULL ] [ 0, "2 2" ] ========

Hope that's what you need ...

Stefan

On Tue, Jul 13, 2010 at 01:37:00PM +0800, Mike Jason wrote:

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Hi, I need some help on how to write some special functions that

monetdb

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currently doesn't have.

E.g., I want to use the oralce funtion nvl(), which is described as follows:

http://download.oracle.com/docs/cd/B19306_01/server.102/b14200/functions105....

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Then, how can I write a function that has the some ability as the

oralce's?

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By the way, now I use MonetDB-Feb2010.

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-- | Dr. Stefan Manegold | mailto:Stefan.Manegold@cwi.nl | | CWI, P.O.Box 94079 | http://www.cwi.nl/~manegold/http://www.cwi.nl/%7Emanegold/ | | 1090 GB Amsterdam | Tel.: +31 (20) 592-4212 | | The Netherlands | Fax : +31 (20) 592-4199 |

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