我想使用NVL2函数创建索引：
create index i_name on PERSON (
NVL2(date1,date2,date3)
);
此打印错误：
Routine (nvl2) can not be resolved.
我想念的是什么？为什么这不起作用
答案 0 :(得分：2)
NVL2的使用不可用，因为功能索引不接受内置函数。以下是在Informix中使用功能索引的基本规则（v12.10）： （quoted from the manual）
重要说明：数据库服务器对以下内容施加了以下限制 功能索引所在的用户定义例程（UDR） 定义：
- 参数不能是集合数据类型的列值。
- 该函数无法返回大对象（包括内置类型BLOB，BYTE，CLOB和TEXT）。
- 该功能不能是VARIANT功能。
- 该函数不能包含任何SQL的DML语句。
- 该功能必须是UDR，而不是内置功能。但是，您可以创建一个调用并返回的SPL包装器 来自SQL的内置函数的值。
我在这里复制一个有效的例子，你可以在你的环境中运行以进行测试 也许需要一些调整，因为我在版本11.70运行它并设置我自己的dbspaces ....
$ cat test.sql
database sysutils;
-- showing my version of informix...
select dbinfo('version','full') from sysmaster:sysdual;
-- creating a database for this test
drop database if exists teste ;
create database teste in dbadat1dbs with buffered log;
-- registering excompat datablate just to enable the use of the dbms_random function for this example.
execute function sysbldprepare('excompat.1.0', 'create');
-- create my test table
drop table if exists mytables;
create table if not exists mytables ( id int, name char(20), created date, modified date, invalidated date) ;
-- including some records...
insert into mytables(id,name,created) select tabid, tabname , created from sysmaster:systables;
-- creating some random data for this example
update mytables set modified = dbinfo('utc_to_datetime',dbms_random_random()) where name matches '*[xmfz]*';
update mytables set invalidated = dbinfo('utc_to_datetime',dbms_random_random()) where modified is not null;
-- trying use the nvl2... which is not possible because it is a builtin function
create index i1_mytables on mytables ( nvl2(modified, created, invalidated)) ;
-- creating my own function, non variant mode.
drop function if exists my_nvl2_date;
create function if not exists my_nvl2_date ( dt date , is_null date, not_null date )
returning date
with (not variant)
return nvl2(dt, is_null, not_null) ;
end function
;
-- create the index
create index i1_mytables on mytables ( my_nvl2_date(modified, created, invalidated)) ;
set explain file to 'test.out' ;
select first 20 * from mytables;
-- here, the index will be used
select first 20 * from mytables where my_nvl2_date(modified, created, invalidated) >= '01/01/2000';
-- this will not use the index because don't match exactly the parameters
select first 20 * from mytables where my_nvl2_date(modified, invalidated, created) >= '01/01/2000';
这是执行。 注意解释文件，在使用索引时显示，而不是。
$ dbaccess -e - test.sql
database sysutils;
Database selected.
-- showing my version of informix...
select dbinfo('version','full') from sysmaster:sysdual;
(constant)
IBM Informix Dynamic Server Version 11.70.FC6
1 row(s) retrieved.
-- creating a database for this test
drop database if exists teste ;
Database dropped.
create database teste in dbadat1dbs with buffered log;
Database closed.
Database created.
-- registering excompat datablate just to enable the use of the dbms_random function for this example.
execute function sysbldprepare('excompat.1.0', 'create');
(expression)
0
1 row(s) retrieved.
-- create my test table
drop table if exists mytables;
Table dropped.
create table if not exists mytables ( id int, name char(20), created date, modified date, invalidated date) ;
Table created.
-- including some records...
insert into mytables(id,name,created) select tabid, tabname , created from sysmaster:systables;
276 row(s) inserted.
-- creating some random data for this example
update mytables set modified = dbinfo('utc_to_datetime',dbms_random_random()) where name matches '*[xmfz]*';
113 row(s) updated.
update mytables set invalidated = dbinfo('utc_to_datetime',dbms_random_random()) where modified is not null;
113 row(s) updated.
-- trying use the nvl2... which is not possible because it is a builtin function
create index i1_mytables on mytables ( nvl2(modified, created, invalidated)) ;
674: Routine (nvl2) can not be resolved.
Error in line 26
Near character position 75
-- creating my own function, non variant mode.
drop function if exists my_nvl2_date;
Routine dropped.
create function if not exists my_nvl2_date ( dt date , is_null date, not_null date )
returning date
with (not variant)
return nvl2(dt, is_null, not_null) ;;
end function
;
Routine created.
;
-- create the index
create index i1_mytables on mytables ( my_nvl2_date(modified, created, invalidated)) ;
Index created.
set explain file to 'test.out' ;
Explain set.
select first 20 * from mytables;
id name created modified invalidated
1 systables 05/06/2013
2 syscolumns 05/06/2013 22/10/1942 13/04/2034
3 sysindices 05/06/2013
4 systabauth 05/06/2013
5 syscolauth 05/06/2013
6 sysviews 05/06/2013
7 sysusers 05/06/2013
8 sysdepend 05/06/2013
9 syssynonyms 05/06/2013 15/03/1981 19/05/1963
10 syssyntable 05/06/2013
11 sysconstraints 05/06/2013
12 sysreferences 05/06/2013 15/08/1912 09/06/1956
13 syschecks 05/06/2013
14 sysdefaults 05/06/2013 09/01/1959 01/03/1943
15 syscoldepend 05/06/2013
16 sysprocedures 05/06/2013
17 sysprocbody 05/06/2013
18 sysprocplan 05/06/2013
19 sysprocauth 05/06/2013
20 sysblobs 05/06/2013
20 row(s) retrieved.
-- here, the index will be used
select first 20 * from mytables where my_nvl2_date(modified, created, invalidated) >= '01/01/2000';
id name created modified invalidated
2 syscolumns 05/06/2013 22/10/1942 13/04/2034
9 syssynonyms 05/06/2013 15/03/1981 19/05/1963
12 sysreferences 05/06/2013 15/08/1912 09/06/1956
14 sysdefaults 05/06/2013 09/01/1959 01/03/1943
25 sysfragments 05/06/2013 29/10/1951 11/02/1953
28 sysfragauth 05/06/2013 06/12/2024 03/11/1948
30 sysxtdtypes 05/06/2013 20/03/1909 03/05/1975
32 sysxtddesc 05/06/2013 23/04/1933 23/07/1961
35 syslogmap 05/06/2013 01/03/2015 30/05/2020
37 sysxtdtypeauth 05/06/2013 16/03/1911 26/12/2037
40 sysams 05/06/2013 02/06/1940 19/08/2000
41 systabamdata 05/06/2013 21/04/2032 17/02/1907
45 systracemsgs 05/06/2013 14/04/2006 09/11/1936
49 sysxasourcetypes 05/06/2013 03/04/1994 28/05/1972
50 sysxadatasources 05/06/2013 09/09/1967 29/11/1978
51 sysseclabelcomponent 05/06/2013 26/04/1979 21/09/1984
52 sysseclabelcomponent 05/06/2013 10/10/2035 16/06/2021
54 syssecpolicycomponen 05/06/2013 23/08/1962 20/05/1983
55 syssecpolicyexemptio 05/06/2013 09/01/1966 04/12/2027
57 sysseclabelnames 05/06/2013 09/03/1948 03/09/1937
20 row(s) retrieved.
-- this will not use the index because don't match exactly the parameters
select first 20 * from mytables where my_nvl2_date(modified, invalidated, created) >= '01/01/2000';
id name created modified invalidated
1 systables 05/06/2013
2 syscolumns 05/06/2013 22/10/1942 13/04/2034
3 sysindices 05/06/2013
4 systabauth 05/06/2013
5 syscolauth 05/06/2013
6 sysviews 05/06/2013
7 sysusers 05/06/2013
8 sysdepend 05/06/2013
10 syssyntable 05/06/2013
11 sysconstraints 05/06/2013
13 syschecks 05/06/2013
15 syscoldepend 05/06/2013
16 sysprocedures 05/06/2013
17 sysprocbody 05/06/2013
18 sysprocplan 05/06/2013
19 sysprocauth 05/06/2013
20 sysblobs 05/06/2013
21 sysopclstr 05/06/2013
22 systriggers 05/06/2013
23 systrigbody 05/06/2013
20 row(s) retrieved.
Database closed.
这是解释文件，执行了3个选择。 仅观察使用索引的第二个选择。
$ cat test.out
QUERY: (OPTIMIZATION TIMESTAMP: 03-21-2014 21:43:22)
------
select first 20 * from mytables
Estimated Cost: 0
Estimated # of Rows Returned: 276
1) informix.mytables: SEQUENTIAL SCAN
Query statistics:
-----------------
The final cost of the plan is reduced because of the FIRST n specification in
the query.
Table map :
----------------------------
Internal name Table name
----------------------------
t1 mytables
type table rows_prod est_rows rows_scan time est_cost
-------------------------------------------------------------------
scan t1 20 276 38 00:00.00 1
QUERY: (OPTIMIZATION TIMESTAMP: 03-21-2014 21:43:22)
------
select first 20 * from mytables where my_nvl2_date(modified, created, invalidated) >= '01/01/2000'
Estimated Cost: 1
Estimated # of Rows Returned: 92
1) informix.mytables: INDEX PATH
(1) Index Name: informix.i1_mytables
Index Keys: informix.my_nvl2_date(modified,created,invalidated) (Serial, fragments: ALL)
Lower Index Filter: informix.my_nvl2_date(informix.mytables.modified ,informix.mytables.created ,informix.mytables.invalidated )>= 01/01/2000
UDRs in query:
--------------
UDR id : 540
UDR name: my_nvl2_date
UDR id : 540
UDR name: my_nvl2_date
Query statistics:
-----------------
The final cost of the plan is reduced because of the FIRST n specification in
the query.
Table map :
----------------------------
Internal name Table name
----------------------------
t1 mytables
type table rows_prod est_rows rows_scan time est_cost
-------------------------------------------------------------------
scan t1 20 92 20 00:00.00 1
QUERY: (OPTIMIZATION TIMESTAMP: 03-21-2014 21:43:22)
------
select first 20 * from mytables where my_nvl2_date(modified, invalidated, created) >= '01/01/2000'
Estimated Cost: 2
Estimated # of Rows Returned: 92
1) informix.mytables: SEQUENTIAL SCAN
Filters: informix.my_nvl2_date(informix.mytables.modified ,informix.mytables.invalidated ,informix.mytables.created )>= 01/01/2000
UDRs in query:
--------------
UDR id : 540
UDR name: my_nvl2_date
Query statistics:
-----------------
The final cost of the plan is reduced because of the FIRST n specification in
the query.
Table map :
----------------------------
Internal name Table name
----------------------------
t1 mytables
type table rows_prod est_rows rows_scan time est_cost
-------------------------------------------------------------------
scan t1 20 92 38 00:00.00 3