SELECT EMPLOYEE_ID ID, FIRST_NAME FNAME, LAST_NAME LNAME FROM EMPLOYEES In these cases the use of NVL() does not work, you should therefore useĬOALESCE() for queries against Oracle DatabaseĬASE / WHEN for Oracle BI EE (logical) queries If no parameter is selected (null), then return all.Īllow selection of multiple parameter values Often report consumers must run reports that support the following conditions: (Select hg.geography_code from hz_geographies hgĪnd hg.geography_type = 'STATE') state_code Identifier,(select person_number from per_all_people_f ppfĪnd :p_effective_start_date between ppf.effective_start_date and ppf.effective_ Identifiers pni where pni.person_id = pprd.person_id and rownum<2) national_ National_identifiers,(select national_identifier_number from per_national National_identifiers pni where pni.person_id = pprd.person_id and rownum<2) (select pprd.person_id,(select REPLACE(national_identifier_number,'-') from per_ NATIONAL_IDENTIFIERS,NATIONAL_IDENTIFIER, If this query returns only a few rows this approach may work satisfactorily however, if the query returns 10000 rows, then each sub or inline query executes 10000 times and the query would likely result in Stuck threads. Avoid using in-line sub queries whenever possible.Īvoid the following use of in-line queries. Altogether, it is 100 multiplied by 1000 times.This is not scalable and cannot perform well. For example, if a main query has 100 columns, and brings 1000 rows, then each column query executes 1000 times. In-line queries execute for each column for each row. Q2 as (SELECT DEPARTMENT_ID EDID,EMPLOYEE_ID EID,FIRST_NAME FNAME,LAST_NAME LNAME,SALARY SAL,COMMISSION_PCT COMMĩ.2.9 Avoid In-Line Queries (as summary columns) WITH Q1 as (SELECT DEPARTMENT_ID DID,DEPARTMENT_NAME DNAME,LOCATION_ID LOC SELECT DEPARTMENT_ID DID,DEPARTMENT_NAME DNAME,LOCATION_ID LOCFROM DEPARTMENTSĬombine the these queries into one using WITH clause as follows: SELECT DEPARTMENT_ID EDID,EMPLOYEE_ID EID,FIRST_NAME FNAME,LAST_NAME LNAME,SALARY SAL,COMMISSION_PCT COMMFROM EMPLOYEES Although the execution of each child query takes less than a second, for each distribution hitting the child query can result in STUCK threads. For example, an invoice distribution table linked to an invoice table where the distribution table has millions of rows compared to the invoice table. When the parent query has many more rows compared to the child query. When the parent and child have a 1-to-1 relationship that is, each parent row has exactly one child row, then merge the parent and child data sets into a single query. When a data model has many nested parent-child relationships slow processing can result.Ī better approach to avoid nested data sets is to combine multiple data set queries into a single query using the WITH clause.įollowing are some general tips about when to combine multiple data sets into one data set: At run time, the data processor executes the parent query and for each row in the parent executes the child query. The data model provides a mechanism to create parent-child hierarchy by linking elements from one data set to another.
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