I have a query as below
select substr( 'ORACLE DEVELOPER',level,1 ) ITEM
from dual connect by level <= length('ORACLE DEVELOPER') ;
it returns 'O' as the result.
but if i put this as a subquery in other it is displaying the required output.
query is as below.
select a.ITEM from (select substr( 'ORACLE DEVELOPER',level,1 ) ITEM
from dual connect by level <= length('ORACLE DEVELOPER') ) a
How this CONNECT BY is working in subquery.
I am new to this feature. Can anyone explain this??
CONNECT BY is Oracle SQL syntax for doing hierarchical queries. Some good examples are here.
One of the side effects is that it allows you to query a single data source multiple times, which means that there's a handy trick to generate any number of rows with:
SELECT 1
FROM dual
CONNECT BY LEVEL <= 10;
The above will connect dual back to itself 10 times - the LEVEL pseudocolumn is from the hierarchy; because the CONNECT BY clause doesn't actually refer to any data from the rowsource, it effectively makes dual its own child, grandchild, great-grandchild, etc. until the CONNECT BY clause evaluates to false (in this case, when LEVEL becomes greater than 10).
In your case, you are generating a row for each letter of the string (instead of 10, you are referring to LENGTH('a string'), which is a nice way of getting a query to return one record for each letter in the string. You are then using SUBSTR to pick out the nth letter from the string.
Related
I have a column named voucher_number. The data in this column looks like
1, 2
I want a query (in oracle and linq as well) to return 0,3,4,5,6,7,8,9,10
Note: i am taking range (0 to 10 )as a parameter parameter from screen(aspx page)
You can use MINUS operator as following:
Select voucher_num from
(
(Select level - 1 as voucher_num from dual
Connect by level <= 11)
Minus
(Select voucher_number from your_table)
)
Order by voucher_num;
Cheers!!
I'm new to Oracle and recently ran into the following query. I'm trying to understand what it's doing and hopefully rewrite it to optimize it. In this example, :NameList would be a comma separated list (like: "Bob,Bill,Fred") and then :N_NameList would be the number of tokens (in above example, 3)
SELECT ... FROM
(
SELECT
REGEXP_SUBSTR(:NameList,'[^,]+',1,LEVEL, 'i') Name
FROM DUAL CONNECT BY LEVEL <= :N_NameList
) x
INNER JOIN PEOPLE ppl
ON ppl.Name LIKE x.Name
...
From what I can tell, it expands out the delimited list into unique rows and then joins it with the following tables for each name, but I'm not sure if that's all it's doing. If that is the case, is there a better way to accomplish this?
You could try this instead:
select ...
from people ppl
where instr (','||:NameList||',',
','||ppl.name||',') > 0;
is there a better way to accomplish this?
Well, you could get rid of N_NameList because you can easily count number of tokens. This doesn't mean that it is a better way, it's just a different option. To be honest, it is probably slower option than yours as I have to calculate something that you entered as a parameter.
As this example is based on SQLPlus, I've used & instead of : for substitution variables. && means that it'll "remember" previously entered value (otherwise, I should type NameList twice.
Your current query:
SQL> select regexp_substr('&namelist', '[^,]+', 1, level, 'i') name
2 from dual
3 connect by level <= &n_namelist;
Enter value for namelist: Bob,Bill,Fred
Enter value for n_namelist: 3
Bob
Bill
Fred
Calculated N_NameList (using REGEXP_COUNT):
SQL> select regexp_substr('&&namelist', '[^,]+', 1, level, 'i') name
2 from dual
3 connect by level <= regexp_count('&&namelist', ',') + 1;
Enter value for namelist: Bob,Bill,Fred
Bob
Bill
Fred
I'm wondering if it's possible to pass one or more parameters to a WITH clause query; in a very simple way, doing something like this (taht, obviously, is not working!):
with qq(a) as (
select a+1 as increment
from dual
)
select qq.increment
from qq(10); -- should get 11
Of course, the use I'm going to do is much more complicated, since the with clause should be in a subquery, and the parameter I'd pass are values taken from the main query....details upon request... ;-)
Thanks for any hint
OK.....here's the whole deal:
select appu.* from
(<quite a complex query here>) appu
where not exists
(select 1
from dual
where appu.ORA_APP IN
(select slot from
(select distinct slots.inizio,slots.fine from
(
with
params as (select 1900 fine from dual)
--params as (select app.ora_fine_attivita fine
-- where app.cod_agenda = appu.AGE
-- and app.ora_fine_attivita = appu.fine_fascia
--and app.data_appuntamento = appu.dataapp
--)
,
Intervals (inizio, EDM) as
( select 1700, 20 from dual
union all
select inizio+EDM, EDM from Intervals join params on
(inizio <= fine)
)
select * from Intervals join params on (inizio <= fine)
) slots
) slots
where slots.slot <= slots.fine
)
order by 1,2,3;
Without going in too deep details, the where condition should remove those records where 'appu.ORA_APP' match one of the records that are supposed to be created in the (outer) 'slots' table.
The constants used in the example are good for a subset of records (a single 'appu.AGE' value), that's why I should parametrize it, in order to use the commented 'params' table (to be replicated, then, in the 'Intervals' table.
I know thats not simple to analyze from scratch, but I tried to make it as clear as possible; feel free to ask for a numeric example if needed....
Thanks
I'm struggling with getting a query to work, and I could really use some help. We have an in house app that we use for building small web apps where I work. It's basically a drag and drop GUI. There's functionality built in to access query string values using the key.
I'm passing a comma separated list of values into a page through the query string. I'm then trying to use the list of values as part of an in clause in a query.
I can see that the value is correct in the query string.
orders=1,2,3
Here's the specific part of the query
"AND OrderNumber IN (this is where it maps from the query string)
I've tried running similar queries in Toad, and I think I've found the issue. It's giving an invalid number error, and I think it's wrapping the query string value in single quotes. I can replicate the error when I do "AND OrderNumber IN ('1,2,3')" in Toad.
Here's where I get really confused. The following works in Toad.
"AND OrderNumber IN ('1','2','3')"
So I tried recreating that by doing
select replace('1,2,3', ',', chr(39)||','||chr(39)) from dual;
I have confirmed that returns '1','2','3' in Toad.
However, I still get an Invalid Number error when I run the following in Toad.
AND OrderNumber IN (replace('1,2,3', ',', chr(39)||','||chr(39))
I've been racking my brain over this, and I can't figure it out. It seems to me that if "AND OrderNumber IN ('1','2','3')" works, and replace('1,2,3', ',', chr(39)||','||chr(39)) returns '1','2','3', that "AND OrderNumber IN (replace('1,2,3', ',', chr(39)||','||chr(39))" should work.
Any help you might be able to offer on this would be greatly appreciated. I know the rest of the query works. That's why I didn't post it. I'm just stuck on trying to get this IN clause working.
A change to phonetic_man's answer that will allow for NULL elements in the list. The regex format of '[^,]+' for parsing delimited lists does not handle NULL list elements and will return an incorrect value if one exists and thus its use should be avoided. Change the original by deleting the number 2 for instance and see the results. You will get a '3' in the 2nd element's position! Here's a way that handles the NULL and returns the correct value for the element:
SELECT TRIM(REGEXP_SUBSTR(str, '(.*?)(,|$)', 1, LEVEL, NULL, 1)) str
FROM ( SELECT '1,,3,4' str FROM dual )
connect by level <= regexp_count(str, ',') + 1;
See here for more info and proof: https://stackoverflow.com/a/31464699/2543416
Can you try the following query.
SELECT * FROM orders
WHERE orderno IN
(
SELECT TRIM(REGEXP_SUBSTR(str, '[^,]+', 1, LEVEL)) str
FROM ( SELECT '1,2,3,4' str FROM dual )
CONNECT BY INSTR(str, ',', 1, LEVEL - 1) > 0
)
The inline query splitting the string in different rows. So, on executing it you will get the following result.
SELECT trim(regexp_substr(str, '[^,]+', 1, LEVEL)) str
FROM ( SELECT '1,2,3,4' str FROM dual )
CONNECT BY instr(str, ',', 1, LEVEL - 1) > 0
1
2
3
4
Now, passing this result to the main query IN clause should work.
I think the desired clause to be built is:
AND OrderNumber IN (1,2,3)
A numeric list. The example you tested:
AND OrderNumber IN ('1','2','3')
works because an implicit conversion from a VARCHAR2 to a NUMBER is occurring for each element in the list.
The following clause will not work because no implicit conversion of the string '1,2,3' can be made (note the clause has a single string element):
AND OrderNumber IN ('1,2,3')
When doing a replace, you are converting the single string: 1,2,3 with the single string: 1','2','3 and this single string cannot be implicitly converted to a number.
I'm trying to use data in sys_context form to perform a match in a WHERE clause.
What I put into the context is ('53','89'), which is what is returned when I select against dual.
My where statement is: where to_char(location_id) in sys_context('my_ctx','valoc')
Since I'm not getting the expected response, I'm guessing that what I think Oracle should see is not actually what it sees, but I don't know how to "look" at what's passed to the processor from TOAD.
The original form was where location_id in sys_context('my_ctx','valoc') with (53,89) in valoc, but that didn't return anything either. I'm sensing there may be no answer to my problem.
The problem is that the resulting WHERE clause is equivalent to this:
where to_char(location_id) in '('53','89')'
(didn't double the inner apostrophes for clarity)
The database sees what's retrieved from context as a single value, not as a list of values.
You can use the CONNECT BY trick to achieve your goal:
SELECT 1
FROM dual
WHERE '53' IN ( -- replace '53' with TO_CHAR(location_id)
SELECT regexp_substr('53,89', '[0-9]*', 1, level) -- replace '53,89' with sys_context('my_ctx','valoc')
FROM dual
CONNECT BY regexp_substr('53,89', '[0-9]*', 1, level) IS NOT NULL -- replace '53,89' with sys_context('my_ctx','valoc')
);