Using Oracle PL/SQL is there a simple equivalent of the following set of T-SQL statements? It seems that everything I am finding is either hopelessly outdated or populates a table data type with no explanation on how to use the result other than writing values to stdout.
declare #tempSites table (siteid int)
insert into #tempSites select siteid from site where state = 'TX'
if 10 > (select COUNT(*) from #tempSites)
begin
insert into #tempSites select siteid from site where state = 'OK'
end
select * from #tempSites ts inner join site on site.siteId = ts.siteId
As #AlexPoole points out in his comment, this is a fairly contrived example.
What I am attempting to do is get all sites that meet a certain set of criteria, and if there are not enough matches, then I am looking to use a different set of criteria.
Oracle doesn't have local temporary tables, and global temporary tables don't look appropriate here.
You could use a common table expression (subquery factoring):
with tempSites (siteId) as (
select siteid
from site
where state = 'TX'
union all
select siteid
from site
where state = 'OK'
and (select count(*) from site where state = 'TX') < 10
)
select s.*
from tempSites ts
join site s on s.siteid = ts.siteid;
That isn't quite the same thing, but gets all the TX IDs, and only includes the OK ones if the count of TX ones - which has to be repeated - is less than 10. The CTE is then joined back to the original table, which all seems a bit wasteful; you're hitting the same table three times.
You could use a subquery directly in a filter instead:
select *
from site
where state = 'TX'
or (state = 'OK'
and (select count(*) from site where state = 'TX') < 10);
but again the TX sites have to be retrieved (or at least counted) a second time.
You can do this with a single hit of the table using an inline view (or CTE if you prefer) with an analytic count - which add the count of TX rows to the columns in the actual table, so you'd probably want to exclude that dummy column from the final result set (but using * is bad practice anyway):
select * -- but list columns, excluding tx_count
from (
select s.*,
count(case when state = 'TX' then state end) over (partition by null) as tx_count
from site s
where s.state in ('TX', 'OK')
)
where state = 'TX'
or (state = 'OK' and tx_count < 10);
From your description of your research it sounds like what you've been looking at involved PL/SQL code populating a collection, which you could still do, but it's probably overkill unless your real situation is much more complicated.
Related
This is an oracle system. I have a client table (one) and an account table (many). Frankly, I really just want to query the client table but due to poor design, there is a data element that I need for the client table that is only present on the account table - it will be the same value for all accounts for that client so I really just need to return one account row but I'm having problems accomplishing this. Here is the query I tried:
Select
c.client_num,
c.client_name,
a.agency_value
from client c
inner join account a on c.client_num = a.client_num
where a.account_num in (select a2.account_num from account a2 where rownum = 1)
You need to explicitly designate how to pick one record out of many. Here's one method - use MAX
Select
c.client_num,
c.client_name,
(SELECT
MAX(a.agency_value) agency_value
FROM account a
where c.client_num = a.client_num
-- not sure if this line is required - if not please remove
and a.account_num in (select a2.account_num from account a2 where rownum = 1)
) agency_value
from client c
Keep in mind that by implementing this you are "cementing" your bad table design.
Are you absolutely certain that there is only ever one agency_value? use query to find any clients that have more than one agency:
SELECT
a.client_num,
COUNT(DISTINCT a.agency_value) CountOfAgencyValues,
MAX(a.agency_value) max_agency_value,
MIN(a.agency_value) max_agency_value
FROM account a
GROUP BY a.client_num
HAVING COUNT(DISTINCT a.agency_value) > 1
With your input and doing some playing around on my own, here is the code that ultimately addressed my need:
select
c. client_num,
(select a.agency_value
from account a
where a.client_num = c.client_num
and rownum = 1)
from client c
So I'm trying to build a function that returns the records of items that are included in some client subscription.
So I've been building up the following:
2 types:
CREATE OR REPLACE TYPE PGM_ROW AS OBJECT
(
pID NUMBER(10),
pName VARCHAR2(300)
);
CREATE OR REPLACE TYPE PGM_TAB AS TABLE OF PGM_ROW;
1 function:
CREATE OR REPLACE FUNCTION FLOGIN (USER_ID NUMBER) RETURN PGM_TAB
AS
SELECTED_PGM PGM_TAB;
BEGIN
FOR RESTRICTION
IN ( SELECT (SELECT LISTAGG (ID_CHANNEL, ',')
WITHIN GROUP (ORDER BY ID_CHANNEL)
FROM (SELECT DISTINCT CHA2.ID_CHANNEL
FROM CHANNELS_ACCESSES CHA2
JOIN CHANNELS CH2
ON CH2.ID = CHA2.ID_CHANNEL
WHERE CHA2.ID_ACCESS = CMPA.ID_ACCESS
AND CH2.ID_CHANNELS_GROUP = CG.ID))
AS channels,
(SELECT LISTAGG (ID_SUBGENRE, ',')
WITHIN GROUP (ORDER BY ID_SUBGENRE)
FROM (SELECT DISTINCT SGA2.ID_SUBGENRE
FROM SUBGENRES_ACCESSES SGA2
JOIN CHANNELS_ACCESSES CHA2
ON CHA2.ID_ACCESS = SGA2.ID_ACCESS
JOIN CHANNELS CH2
ON CH2.ID = CHA2.ID_CHANNEL
WHERE SGA2.ID_ACCESS = CMPA.ID_ACCESS
AND CH2.ID_CHANNELS_GROUP = CG.ID))
AS subgenres,
CG.NAME,
A.BEGIN_DATE,
A.END_DATE,
CMP.PREVIEW_ACCESS
FROM USERS U
JOIN COMPANIES_ACCESSES CMPA
ON U.ID_COMPANY = CMPA.ID_COMPANY
JOIN COMPANIES CMP ON CMP.ID = CMPA.ID_COMPANY
JOIN ACCESSES A ON A.ID = CMPA.ID_ACCESS
JOIN CHANNELS_ACCESSES CHA
ON CHA.ID_ACCESS = CMPA.ID_ACCESS
JOIN SUBGENRES_ACCESSES SGA
ON SGA.ID_ACCESS = CMPA.ID_ACCESS
JOIN CHANNELS CH ON CH.ID = CHA.ID_CHANNEL
JOIN CHANNELS_GROUPS CG ON CG.ID = CH.ID_CHANNELS_GROUP
WHERE U.ID = USER_ID
GROUP BY CG.NAME,
A.BEGIN_DATE,
A.END_DATE,
CMPA.ID_ACCESS,
CG.ID,
CMP.PREVIEW_ACCESS)
LOOP
SELECT PFT.ID_PROGRAM, PFT.LOCAL_TITLE
BULK COLLECT INTO SELECTED_PGM
FROM PROGRAMS_FT PFT
WHERE PFT.ID_CHANNEL IN
( SELECT TO_NUMBER (
REGEXP_SUBSTR (RESTRICTION.CHANNELS,
'[^,]+',
1,
ROWNUM))
FROM DUAL
CONNECT BY LEVEL <=
TO_NUMBER (
REGEXP_COUNT (RESTRICTION.CHANNELS,
'[^,]+')))
AND PFT.ID_SUBGENRE IN
( SELECT TO_NUMBER (
REGEXP_SUBSTR (RESTRICTION.SUBGENRES,
'[^,]+',
1,
ROWNUM))
FROM DUAL
CONNECT BY LEVEL <=
TO_NUMBER (
REGEXP_COUNT (RESTRICTION.SUBGENRES,
'[^,]+')))
AND (PFT.LAUNCH_DATE BETWEEN RESTRICTION.BEGIN_DATE
AND RESTRICTION.END_DATE);
END LOOP;
RETURN SELECTED_PGM;
END FLOGIN;
I expect the function tu return a table with 2 columns containing all the records from table PROGRAMS_FT that are included in the user access.
For some reason, I'm getting compilation warning ORA-000947.
My understanding of the error code is that it occurs when the values inserted does not match the type of the object receiving the values, and I can't see how this can be the case here.
You're selecting two scalar values and trying to put them into an object. That doesn't happen automatically, you need to convert them to an object:
...
LOOP
SELECT PGM_ROW(PFT.ID_PROGRAM, PFT.LOCAL_TITLE)
BULK COLLECT INTO SELECTED_PGM
FROM PROGRAMS_FT PFT
...
(It's an unhelpful quirk of PL/SQL that it says 'not enough values' rather than 'too many values', as you might expect when you try to put two things into one; I'm sure I came up with a fairly convincing explanation/excuse for that once but it escapes me at the moment...)
I'm not sure your loop makes sense though. Assuming your cursor query returns multiple rows, each time around the loop you're replacing the contents of the SELECTED_PGM collection - you might think you are appending to it, but that's not how it works. So you will end up returning a collection based only on the final iteration of the loop.
Aggregating and then splitting the data seems like a lot of work too. You could maybe use collections for those; but you can probably get rid of the cursor and loop and combine the cursor query with the inner query, which would be more efficient and would allow you to do a single bulk-collect for all the combined data.
We're using Oracle 10g XE and we found that the following query didn't return any value:
SELECT ref.referencia,
ref.descripcio,
stock_reservat,
stock,
stock_p_rebre,
(SELECT count(*)
FROM ref_numeros_serie num
WHERE num.empresa=ref.empresa AND
num.referencia=ref.referencia AND
num.diposit=1 AND
nvl(num.actiu,'N')='S') cnt_nums_serie
FROM emp_referencies ref,
ref_stk_dip_acu stk
WHERE ref.empresa=1 AND
ref.referencia='1B' AND
stk.empresa=ref.empresa AND
stk.referencia=ref.referencia AND
stk.diposit=1 AND
-- Relevant part
(stk.stock - stk.stock_reservat) <> (SELECT count(*)
FROM ref_numeros_serie num
WHERE num.empresa=ref.empresa AND
num.referencia=ref.referencia AND
num.diposit=1 AND
nvl(num.actiu,'N')='S')
-- End of relevant part
GROUP BY ref.empresa,
ref.referencia,
ref.descripcio,
stk.stock,
stk.stock_reservat,
stock,
stock_p_rebre
So the comparison between the subtraction and the subquery was false. But if we swapped the subquery and the subtraction like this:
SELECT ref.referencia,ref.descripcio,
stock_reservat,
stock,
stock_p_rebre,
(SELECT count(*)
FROM ref_numeros_serie num
WHERE num.empresa=ref.empresa AND
num.referencia=ref.referencia AND
num.diposit=1 AND
nvl(num.actiu,'N')='S') cnt_nums_serie
FROM emp_referencies ref,
ref_stk_dip_acu stk
WHERE ref.empresa=1 AND
ref.referencia='1B' AND
stk.empresa=ref.empresa AND
stk.referencia=ref.referencia AND
stk.diposit=1 AND
-- Relevant part
(SELECT count(*)
FROM ref_numeros_serie num
WHERE num.empresa=ref.empresa AND
num.referencia=ref.referencia AND
num.diposit=1 AND
nvl(num.actiu,'N')='S') <> (stk.stock - stk.stock_reservat)
-- End of relevant part
GROUP BY ref.empresa,
ref.referencia,
ref.descripcio,
stk.stock,
stk.stock_reservat,
stock,
stock_p_rebre
The comparison is true and we get results.
We have tried the following cases:
Removing the second part of the subtraction so the left part of the comparison is stk.stock: we get results, correct
Changing the second part of the subtraction by a number like this stk.stock-2: we get results, correct
Swapping the left and right part of the comparison, as explained above: we get results, correct
Changing the arithmetic operator like this (stk.stock+stk.stock_reservat) <> subquery: no results, incorrect
Changing the subquery by a number like this (stk.stock-stk.stock_reservat) <> 2: we get results, correct
We have tried these cases with a 10g non-XE database and it has the same behaviour. With a 11g, on the other hand, it works perfectly fine.
So our conclusion is that with oracle 10g a comparison between an arithmetic operation between two columns and a subquery works only if the subquery is on the left side and the operation on the right side. Has anybody had a similar problem and how did you work around/fix it?
EDIT: I want to add that this happens when the subquery result is 0, we haven't had issues with it otherwise, i.e. it behaves as expected.
Your query could be simplified by using a subquery factoring clause, as in:
WITH ns AS (SELECT r.empresa, r.referencia, count(*) as CNT_NUMS_SERIE
FROM ref_numeros_serie n
INNER JOIN emp_referencies r
r.empresa = n.empresa AMD
r.referencia = n.referencia
WHERE n.diposit = 1 AND
NVL(n.actiu, 'N') = 'S'
GROUP BY r.empresa,
r.referencia)
SELECT ref.referencia,
ref.descripcio,
stock_reservat,
stock,
stock_p_rebre,
ns.CNT_NUMS_SERIE
FROM emp_referencies ref
INNER JOIN ref_stk_dip_acu stk
ON stk.empresa = ref.empresa AND
stk.referencia = ref.referencia
INNER JOIN ns
ON ns.empresa = ref.empresa AND
ns.referencia = ref.referencia
WHERE ref.empresa = 1 AND
ref.referencia = '1B' AND
stk.diposit = 1 AND
-- Relevant part
(stk.stock - NVL(stk.stock_reservat, 0)) <> ns.CNT_NUMS_SERIE
-- End of relevant part
GROUP BY ref.empresa,
ref.referencia,
ref.descripcio,
stk.stock,
stk.stock_reservat,
stock,
stock_p_rebre
This lets you pull the common expression (SELECT COUNT(*)...) out and treat it as a separate table. I think it makes the query easier to read and might save some execution time.
Share and enjoy.
I've faced with a weird problem now. The query itself is huge so I'm not going to post it here (I could post however in case someone needs to see). Now I have a table ,TABLE1, with a CHAR(1) column, COL1. This table column is queried as part of my query. When I filter the recordset for this column I say:
WHERE TAB1.COL1=1
This way the query runs and returns a very big resultset. I've recently updated one of the subqueries to speed up the query. But after this when I write WHERE TAB1.COL1=1 it does not return anything, but if I change it to WHERE TAB1.COL1='1' it gives me the records I need. Notice the WHERE clause with quotes and w/o them. So to make it more clear, before updating one of the sub-queries I did not have to put quotes to check against COL1 value, but after updating I have to. What feature of Oracle is it that I'm not aware of?
EDIT: I'm posting the tw versions of the query in case someone might find it useful
Version 1:
SELECT p.ssn,
pss.pin,
pd.doc_number,
p.surname,
p.name,
p.patronymic,
to_number(p.sex, '9') as sex,
citiz_c.short_name citizenship,
p.birth_place,
p.birth_day as birth_date,
coun_c.short_name as country,
di.name as leg_city,
trim( pa.settlement
|| ' '
|| pa.street) AS leg_street,
pd.issue_date,
pd.issuing_body,
irs.irn,
irs.tpn,
irs.reg_office,
to_number(irs.insurer_type, '9') as insurer_type,
TO_CHAR(sa.REG_CODE)
||CONVERT_INT_TO_DOUBLE_LETTER(TO_NUMBER(SUBSTR(TO_CHAR(sa.DOSSIER_NR, '0999999'), 2, 3)))
||SUBSTR(TO_CHAR(sa.DOSSIER_NR, '0999999'), 5, 4) CONVERTED_SSN_DOSSIER_NR,
fa.snr
FROM
(SELECT pss_t.pin,
pss_t.ssn
FROM EHDIS_INSURANCE.pin_ssn_status pss_t
WHERE pss_t.difference_status < 5
) pss
INNER JOIN SSPF_CENTRE.file_archive fa
ON fa.ssn = pss.ssn
INNER JOIN SSPF_CENTRE.persons p
ON p.ssn = fa.ssn
INNER JOIN
(SELECT pd_2.ssn,
pd_2.type,
pd_2.series,
pd_2.doc_number,
pd_2.issue_date,
pd_2.issuing_body
FROM
--The changed subquery starts here
(SELECT ssn,
MIN(type) AS type
FROM SSPF_CENTRE.person_documents
GROUP BY ssn
) pd_1
INNER JOIN SSPF_CENTRE.person_documents pd_2
ON pd_2.type = pd_1.type
AND pd_2.ssn = pd_1.ssn
) pd
--The changed subquery ends here
ON pd.ssn = p.ssn
INNER JOIN SSPF_CENTRE.ssn_archive sa
ON p.ssn = sa.ssn
INNER JOIN SSPF_CENTRE.person_addresses pa
ON p.ssn = pa.ssn
INNER JOIN
(SELECT i_t.irn,
irs_t.ssn,
i_t.tpn,
i_t.reg_office,
(
CASE i_t.insurer_type
WHEN '4'
THEN '1'
ELSE i_t.insurer_type
END) AS insurer_type
FROM sspf_centre.irn_registered_ssn irs_t
INNER JOIN SSPF_CENTRE.insurers i_t
ON i_t.irn = irs_t.new_irn
OR i_t.old_irn = irs_t.old_irn
WHERE irs_t.is_registration IS NOT NULL
AND i_t.is_real IS NOT NULL
) irs ON irs.ssn = p.ssn
LEFT OUTER JOIN SSPF_CENTRE.districts di
ON di.code = pa.city
LEFT OUTER JOIN SSPF_CENTRE.countries citiz_c
ON p.citizenship = citiz_c.numeric_code
LEFT OUTER JOIN SSPF_CENTRE.countries coun_c
ON pa.country_code = coun_c.numeric_code
WHERE pa.address_flag = '1'--Here's the column value with quotes
AND fa.form_type = 'Q3';
And Version 2:
SELECT p.ssn,
pss.pin,
pd.doc_number,
p.surname,
p.name,
p.patronymic,
to_number(p.sex, '9') as sex,
citiz_c.short_name citizenship,
p.birth_place,
p.birth_day as birth_date,
coun_c.short_name as country,
di.name as leg_city,
trim( pa.settlement
|| ' '
|| pa.street) AS leg_street,
pd.issue_date,
pd.issuing_body,
irs.irn,
irs.tpn,
irs.reg_office,
to_number(irs.insurer_type, '9') as insurer_type,
TO_CHAR(sa.REG_CODE)
||CONVERT_INT_TO_DOUBLE_LETTER(TO_NUMBER(SUBSTR(TO_CHAR(sa.DOSSIER_NR, '0999999'), 2, 3)))
||SUBSTR(TO_CHAR(sa.DOSSIER_NR, '0999999'), 5, 4) CONVERTED_SSN_DOSSIER_NR,
fa.snr
FROM
(SELECT pss_t.pin,
pss_t.ssn
FROM EHDIS_INSURANCE.pin_ssn_status pss_t
WHERE pss_t.difference_status < 5
) pss
INNER JOIN SSPF_CENTRE.file_archive fa
ON fa.ssn = pss.ssn
INNER JOIN SSPF_CENTRE.persons p
ON p.ssn = fa.ssn
INNER JOIN
--The changed subquery starts here
(SELECT ssn,
type,
series,
doc_number,
issue_date,
issuing_body
FROM
(SELECT ssn,
type,
series,
doc_number,
issue_date,
issuing_body,
ROW_NUMBER() OVER (partition BY ssn order by type) rn
FROM SSPF_CENTRE.person_documents
)
WHERE rn = 1
) pd --
--The changed subquery ends here
ON pd.ssn = p.ssn
INNER JOIN SSPF_CENTRE.ssn_archive sa
ON p.ssn = sa.ssn
INNER JOIN SSPF_CENTRE.person_addresses pa
ON p.ssn = pa.ssn
INNER JOIN
(SELECT i_t.irn,
irs_t.ssn,
i_t.tpn,
i_t.reg_office,
(
CASE i_t.insurer_type
WHEN '4'
THEN '1'
ELSE i_t.insurer_type
END) AS insurer_type
FROM sspf_centre.irn_registered_ssn irs_t
INNER JOIN SSPF_CENTRE.insurers i_t
ON i_t.irn = irs_t.new_irn
OR i_t.old_irn = irs_t.old_irn
WHERE irs_t.is_registration IS NOT NULL
AND i_t.is_real IS NOT NULL
) irs ON irs.ssn = p.ssn
LEFT OUTER JOIN SSPF_CENTRE.districts di
ON di.code = pa.city
LEFT OUTER JOIN SSPF_CENTRE.countries citiz_c
ON p.citizenship = citiz_c.numeric_code
LEFT OUTER JOIN SSPF_CENTRE.countries coun_c
ON pa.country_code = coun_c.numeric_code
WHERE pa.address_flag = 1--Here's the column value without quotes
AND fa.form_type = 'Q3';
I've put separating comments for the changed subqueries and the WHERE clause in both queries. Both versions of the subqueries return the same result, one of them is just slower, which is why I decided to update it.
With the most simplistic example I can't reproduce your problem on 11.2.0.3.0 or 11.2.0.1.0.
SQL> create table tmp_test ( a char(1) );
Table created.
SQL> insert into tmp_test values ('1');
1 row created.
SQL> select *
2 from tmp_test
3 where a = 1;
A
-
1
If I then insert a non-numeric value into the table I can confirm Chris' comment "that Oracle will rewrite tab1.col1 = 1 to to_number(tab1.col1) = 1", which implies that you only have numeric characters in the column.
SQL> insert into tmp_test values ('a');
1 row created.
SQL> select *
2 from tmp_test
3 where a = 1;
ERROR:
ORA-01722: invalid number
no rows selected
If you're interested in tracking this down you should gradually reduce the complexity of the query until you have found a minimal, reproducible, example. Oracle can pre-compute a conversion to be used in a JOIN, which as your query is complex seems like a possible explanation of what's happening.
Oracle explicitly recommends against using implicit conversion so it's wiser not to use it at all; as you're finding out. For a start there's no guarantees that your indexes will be used correctly.
Oracle recommends that you specify explicit conversions, rather than rely on implicit or automatic conversions, for these reasons:
SQL statements are easier to understand when you use explicit data type conversion functions.
Implicit data type conversion can have a negative impact on performance, especially if the data type of a column value is converted to that of a constant rather than the other way around.
Implicit conversion depends on the context in which it occurs and may not work the same way in every case. For example, implicit conversion from a datetime value to a VARCHAR2 value may return an unexpected year depending on the value of the NLS_DATE_FORMAT
parameter.
Algorithms for implicit conversion are subject to change across software releases and among Oracle products. Behavior of explicit conversions is more predictable.
If you do only have numeric characters in the column I would highly recommend changing this to a NUMBER(1) column and I would always recommend explicit conversion to avoid a lot of pain in the longer run.
It's hard to tell without the actual query. What I would expect is that TAB1.COL1 is in some way different before and after the refactoring.
Candidates differences are Number vs. CHAR(1) vs. CHAR(x>1) vs VARCHAR2
It is easy to introduce differences like this with subqueries where you join two tables which have different types in the join column and you return different columns in your subquery.
To hunt that issue down you might want to check the exact datatypes of your query. Not sure how to do that right now .. but an idea would be to put it in a view and use sqlplus desc on it.
Recently I fixed the some bug: there was rownum in the join condition.
Something like this: left join t1 on t1.id=t2.id and rownum<2. So it was supposed to return only one row regardless of the “left join”.
When I looked further into this, I realized that I don’t understand how Oracle evaluates rownum in the "left join" condition.
Let’s create two sampe tables: master and detail.
create table MASTER
(
ID NUMBER not null,
NAME VARCHAR2(100)
)
;
alter table MASTER
add constraint PK_MASTER primary key (ID);
prompt Creating DETAIL...
create table DETAIL
(
ID NUMBER not null,
REF_MASTER_ID NUMBER,
NAME VARCHAR2(100)
)
;
alter table DETAIL
add constraint PK_DETAIL primary key (ID);
alter table DETAIL
add constraint FK_DETAIL_MASTER foreign key (REF_MASTER_ID)
references MASTER (ID);
prompt Disabling foreign key constraints for DETAIL...
alter table DETAIL disable constraint FK_DETAIL_MASTER;
prompt Loading MASTER...
insert into MASTER (ID, NAME)
values (1, 'First');
insert into MASTER (ID, NAME)
values (2, 'Second');
commit;
prompt 2 records loaded
prompt Loading DETAIL...
insert into DETAIL (ID, REF_MASTER_ID, NAME)
values (1, 1, 'REF_FIRST1');
insert into DETAIL (ID, REF_MASTER_ID, NAME)
values (2, 1, 'REF_FIRST2');
insert into DETAIL (ID, REF_MASTER_ID, NAME)
values (3, 1, 'REF_FIRST3');
commit;
prompt 3 records loaded
prompt Enabling foreign key constraints for DETAIL...
alter table DETAIL enable constraint FK_DETAIL_MASTER;
set feedback on
set define on
prompt Done.
Then we have this query :
select * from master t
left join detail d on d.ref_master_id=t.id
The result set is predictable: we have all the rows from the master table and 3 rows from the detail table that matched this condition d.ref_master_id=t.id.
Result Set
Then I added “rownum=1” to the join condition and the result was the same
select * from master t
left join detail d on d.ref_master_id=t.id and rownum=1
The most interesting thing is that I set “rownum<-666” and got the same result again!
select * from master t
left join detail d on d.ref_master_id=t.id and rownum<-666.
Due to the result set we can say that this condition was evaluated as “True” for 3 rows in the detail table. But if I use “inner join” everything goes as supposed to be.
select * from master t
join detail d on d.ref_master_id=t.id and rownum<-666.
This query doesn’t return any row,because I can't imagine rownum to be less then -666 :-)
Moreover, if I use oracle syntax for outer join, using “(+)” everything goes well too.
select * from master m ,detail t
where m.id=t.ref_master_id(+) and rownum<-666.
This query doesn’t return any row too.
Can anyone tell me, what I misunderstand with outer join and rownum?
ROWNUM is a pseudo-attribute of result sets, not of base tables. ROWNUM is defined after rows are selected, but before they're sorted by an ORDER BY clause.
edit: I was mistaken in my previous writeup of ROWNUM, so here's new information:
You can use ROWNUM in a limited way in the WHERE clause, for testing if it's less than a positive integer only. See ROWNUM Pseudocolumn for more details.
SELECT ... WHERE ROWNUM < 10
It's not clear what value ROWNUM has in the context of a JOIN clause, so the results may be undefined. There seems to be some special-case handling of expressions with ROWNUM, for instance WHERE ROWNUM > 10 always returns false. I don't know how ROWNUM<-666 works in your JOIN clause, but it's not meaningful so I would not recommend using it.
In any case, this doesn't help you to fetch the first detail row for each given master row.
To solve this you can use analytic functions and PARTITION, and combine it with Common Table Expressions so you can access the row-number column in a further WHERE condition.
WITH numbered_cte AS (
SELECT *, ROW_NUMBER() OVER (PARTITION BY t.id ORDER BY d.something) AS rn
FROM master t LEFT OUTER JOIN detail d ON d.ref_master_id = t.id
)
SELECT *
FROM numbered_cte
WHERE rn = 1;
if you want to get the first three values from the join condition change the select statement like this.
select *
from (select *
from master t left join detail d on d.ref_master_id=t.id)
where rownum<3;
You will get the required output. Take care on unambigiously defined column names when using *
Let me give an absolute answer which u can run directly with out making any changes to the code.
select *
from (select t.id,t.name,d.id,d.ref_master_id,d.name
from master t left join detail d on d.ref_master_id=t.id)
where rownum<3;
A ROWNUM filter doesn't make any sense in a join, but it isn't being rejected as invalid.
The explain plan will either include the ROWNUM filter or exclude it. If it includes it, it will apply the filter to the detail table after applying the other join condition(s). So if you put in ROWNUM=100 (which will never be satisfied) all the detail rows are excluded and then the outer join kicks in.
If you put in ROWNUM=1 it seems to drop the filter.
And if you query
with
a as (select rownum a_val from dual connect by level < 10),
b as (select rownum*2 b_val from dual connect by level < 10)
select * from a left join b on a_val < b_val and rownum in (1,3);
you get something totally weird.
It probably should be rejected as an error, so expect nonsensical things to happen