I have a query like:
select
qsn.code,
(select prs.display_name from prs where prs.id = qsn.fk_prs) display_name,
(select prs.address from prs where prs.id = qsn.fk_prs) address,
(select prs.tel from prs where prs.id = qsn.fk_prs) tel
from
qsn
where
qsn.register_date between :x1 and :x2
When I look at the execution plan of the query, it queries prs table 3 times (each time using INDEX UNIQUE SCAN).
I wonder if I can query the prs table once using WITH clause? How can I write the query that way.
I shall mention that because each of the tables have millions of record, joining them makes the query so slow.
using with clause your query goes like this:
with abc as (select id,
display_name ,
address ,
tel
from prs)
select
qsn.code,
abc.display_name,
abc.address,
abc.tel
from qsn
inner join abc
on qsn.fk_prs = abc.id
where qsn.register_date between :x1 and :x2 ;
ps: not tested.
Use a join:
select qsn.code, prs.display_name, prs.address, prs.tel
from qsn
left join prs on prs.id = qsn.fk_prs
where qsn.register_date between :x1 and :x2
Related
I have two query that looks close to the same but Oracle have very different performance.
Query A
Create Table T1 as Select * from FinalView1 where CustomerID in ('A0000001','A000002')
Query B
Create Table T1 as Select * from FinalView1 where CustomerID in (select distinct CustomerID from CriteriaTable)
The CriteriaTable have 800 rows but all belongs to Customer ID 'A0000001' and 'A000002'.
This means the subquery: "select distinct CustomerID from CriteriaTable" also only returns the same two elements('A0000001','A000002') as manually entered in query A
Following is the query under the FinalView1
create or replace view FinalView1_20200716 as
select
Customer_ID,
<Some columns>
from
Table1_20200716 T1
INNER join Table2_20200716 T2 on
T1.Invoice_number = T2.Invoice_number
and
T1.line_id = T2.line_id
left join Table3_20200716 T3 on
T3.id = T1.Customer_ID
left join Table4_20200716 T4 on
T4.Shipping_ID = T1.Shipping_ID
left join Table5_20200716 Table5 on
Table5.Invoice_ID = T1.Invoice_ID
left join Table6_20200716 T6 on
T6.Shipping_ID = T4.Shipping_ID
left join First_Order first on
first.Shipping_ID = T1.Shipping_ID
;
Table1_20200716,Table2_20200716,Table3_20200716,Table4_20200716,Table5_20200716,Table6_20200716 are views to the corresponding table with temporal validity feature. For example
The query under Table1_20200716
Create or replace view Table1_20200716 as
select
*
from Table1 as for period of to_date('20200716,'yyyymmdd')
However table "First_Order" is just a normal table as
Following is the performance for both queries (According to explain plan):
Query A:
Cardinality: 102
Cost : 204
Total Runtime: 5 secs max
Query B:
Cardinality:27921981
Cost: 14846
Total Runtime:20 mins until user cancelled
All tables are indexed using those columns that used to join against other tables in the FinalView1. According to the explain plan, they have all been used except for the FirstOrder table.
Query A used uniquue index on the FirstOrder Table while Query B performed a full scan.
For query B, I was expecting the Oracle will firstly query the sub-query get the result into the in operator, before executing the main query and therefore should only have minor impact to the performance.
Thanks in advance!
As mentioned from my comment 2 days ago. Someone have actually posted the solution and then have it removed while the answer actually work. After waiting for 2 days the So I designed to post that solution.
That solution suggested that the performance was slow down by the "in" operator. and suggested me to replace it with an inner join
Create Table T1 as
Select
FV.*
from
FinalView1 FV
inner join (
select distinct
CustomerID
from
CriteriaTable
) CT on CT.customerid = FV.customerID;
Result from explain plan was worse then before:
Cardinality:28364465 (from 27921981)
Cost: 15060 (from 14846)
However, it only takes 17 secs. Which is very good!
Let me explain the question.
I have two tables, which have 3 columns with same data tpyes. The 3 columns create a key/ID if you like, but the name of the columns are different in the tables.
Now I am creating queries with these 3 columns for both tables. I've managed to independently get these results
For example:
SELECT ID, FirstColumn, sum(SecondColumn)
FROM (SELECT ABC||DEF||GHI AS ID, FirstTable.*
FROM FirstTable
WHERE ThirdColumn = *1st condition*)
GROUP BY ID, FirstColumn
;
SELECT ID, SomeColumn, sum(AnotherColumn)
FROM (SELECT JKM||OPQ||RST AS ID, SecondTable.*
FROM SecondTable
WHERE AlsoSomeColumn = *2nd condition*)
GROUP BY ID, SomeColumn
;
So I make a very similar queries for two different tables. I know the results have a certain number of same rows with the ID attribute, the one I've just created in the queries. I need to check which rows in the result are not in the other query's result and vice versa.
Do I have to make temporary tables or views from the queries? Maybe join the two tables in a specific way and only run one query on them?
As a beginner I don't have any experience how to use results as an input for the next query. I'm interested what is the cleanest, most elegant way to do this.
No, you most probably don't need any "temporary" tables. WITH factoring clause would help.
Here's an example:
with
first_query as
(select id, first_column, ...
from (select ABC||DEF||GHI as id, ...)
),
second_query as
(select id, some_column, ...
from (select JKM||OPQ||RST as id, ...)
)
select id from first_query
minus
select id from second_query;
For another result you'd just switch the tables, e.g.
with ... <the same as above>
select id from second_query
minus
select id from first_query
Is it possible to rewrite the following query
SELECT CT.GROUP, CT.EMP_ID, HT.EFF_DT
FROM CURR_TABLE CT
JOIN (SELECT GROUP, EMP_ID, MAX(EFF_DT) AS EFF_DT
FROM HIST_TABLE
WHERE STAT = 'A'
GROUP BY GROUP, EMP_ID) HT ON CT.GROUP = HT.GROUP AND
CT.EMPID = HT.EMP_ID
WHERE CT.GROUP = :1
AND CT.EMP_ID = :2
in a way that is similar to CROSS JOIN style?
SELECT table1.column1, table2.column2...
FROM table1, table2 [, table3 ]
The reason is that I want to create such query in Peoplesoft, and the above can only be achieved by creating a separate view for the selection with the group by clause. I want to do this just in one query without creating additional views.
You may try writing your query as a single level join with an aggregation:
SELECT
CT.GROUP,
CT.EMP_ID,
MAX(HT.EFF_DT) AS EFF_DT
FROM CURR_TABLE CT
LEFT JOIN HIST_TABLE HT
ON CT.GROUP = HT.GROUP AND
CT.EMPID = HT.EMP_ID AND
HT.STAT = 'A'
WHERE
CT.GROUP = :1 AND
CT.EMP_ID = :2
GROUP BY
CT.GROUP,
CT.EMP_ID;
Note that GROUP is a reserved SQL keyword, and you might have to escape it with double quotes to make this query (or the one in your question) work on Oracle.
I was just wondering how you select multiple records from a table column. Please see below the query.
SELECT DISTINCT DEPARTMENT_NAME, CITY, COUNTRY_NAME
FROM OEHR_DEPARTMENTS
NATURAL JOIN OEHR_EMPLOYEES
NATURAL JOIN OEHR_LOCATIONS
NATURAL JOIN OEHR_COUNTRIES
WHERE JOB_ID = 'SA_MAN' AND JOB_ID = 'SA_REP'
;
Basically, I want to be able to select records from the table column I have, however when you use AND it only displays SA_MAN and not SA_REP. I have also tried to use OR and it displays no rows selected. How would I actually be able to select both Job ID's without it just displaying one or the other.
Sorry this may sound like a stupid question (and probably not worded right), but I am pretty new to Oracle 11g SQL.
For your own comfort while debugging, I suggest you to use inner joins instead of natual joins.
That where clause is confusing, if not utterly wrong, because you don't make clear which tables' JOB_ID should be filtered. Use inner joins, give aliases to tables, and refer to those aliases in the where clause.
select distinct DEPARTMENT_NAME, CITY, COUNTRY_NAME
from OEHR_DEPARTMENTS t1
join OEHR_EMPLOYEES t2
on ...
join OEHR_LOCATIONS t3
on ...
join OEHR_COUNTRIES t4
on ...
where tn.JOB_ID = 'SA_MAN' AND tm.JOB_ID = 'SA_REP'
After rephrasing your query somehow like this, you'll have a clearer view on the logical operator you'll have to use in the where clause, which I bet will be an OR.
EDIT (after more details were given)
To list the departments that employ staff with both 'SA_MAN' and 'SA_REP' job_id, you have to join the departments table with the employees twice, once with the filter job_id='SA_MAN' and once with job_id='SA_REP'
select distinct DEPARTMENT_NAME, CITY, COUNTRY_NAME
from OEHR_DEPARTMENTS t1
join OEHR_EMPLOYEES t2
on t1.department_id = t2.department_id --guessing column names
join OEHR_EMPLOYEES t3
on t1.department_id = t3.department_id --guessing column names
join OEHR_LOCATIONS t4
on t1.location_id = t4.location_id --guessing column names
join OEHR_COUNTRIES t5
on t4.country_id = t5.country_id --guessing column names
where t2.job_id = 'SA_MAN' and t3.job_id = 'SA_REP'
order by 1, 2, 3
I have a table pa_master_details and lov_details.
In the pa_master_details table, I have role_comp_emp_final_rating and role_comp_lm_final_rating columns.
In the lov_details table I have a column rating lov_value and lov_text_en.
I need to join role_comp_emp_final_rating with the lov_value column to get lov_text_en
Based on this lov_value, I need to show lov_text_en from the lov_details table.
So I wrote a query like this and am getting the result for emp rating:
SELECT p.employee_number,
p.role_comp_emp_final_rating,
lov_text_en,
p.role_comp_lm_final_rating
FROM pa_master_details P, lov_details L
WHERE p.role_comp_emp_final_rating = l.lov_value
AND p.employee_number = 34570
Similarly, I need to show lov_text_en for role_comp_lm_final_rating from the lov_details table by joining
role_comp_lm_final_rating with lov_value in the same query.
How do I do it?
I think this is what you're asking for:
SELECT p.employee_number,
p.role_comp_emp_final_rating,
lemp.lov_text_en AS "emp_lov_text",
llm.lov_text_en AS "lm_lov_text",
p.role_comp_lm_final_rating
FROM pa_master_details p
JOIN (SELECT lov_text FROM lov_details) lemp ON p.role_comp_emp_final_rating = lemp.lov_value
JOIN (SELECT lov_text FROM lov_details) llm ON p.role_comp_lm_final_rating = llm.lov_value
WHERE p.employee_number = 34570