16f6c0aecf
Inline adoc files when they are included exactly once. Also fix language tags because this inlining gives us better information on what language the code is written in.
91 lines
2.2 KiB
Plaintext
91 lines
2.2 KiB
Plaintext
== Why is this an issue?
|
|
|
|
SQL is an extremely powerful and hard to master language. It may be tempting to emulate SQL joins in PL/SQL using nested cursor loops, but those are not optimized by Oracle at all. In fact, they lead to numerous context switches between the SQL and PL/SQL engines, and those switches have a highly negative impact on performance. It is therefore much better to replace nested PL/SQL cursor loops with native SQL joins.
|
|
|
|
|
|
=== Noncompliant code example
|
|
|
|
[source,sql]
|
|
----
|
|
SET SERVEROUTPUT ON
|
|
|
|
CREATE TABLE countriesTable(
|
|
countryName VARCHAR2(42)
|
|
);
|
|
|
|
CREATE TABLE citiesTable(
|
|
cityName VARCHAR2(42)
|
|
);
|
|
|
|
INSERT INTO countriesTable VALUES('India');
|
|
INSERT INTO countriesTable VALUES('Switzerland');
|
|
INSERT INTO countriesTable VALUES('United States');
|
|
|
|
INSERT INTO citiesTable VALUES('Berne');
|
|
INSERT INTO citiesTable VALUES('Delhi');
|
|
INSERT INTO citiesTable VALUES('Bangalore');
|
|
INSERT INTO citiesTable VALUES('New York');
|
|
|
|
BEGIN
|
|
FOR countryRecord IN (SELECT countryName FROM countriesTable) LOOP
|
|
FOR cityRecord IN (SELECT cityName FROM citiesTable) LOOP -- Non-Compliant
|
|
DBMS_OUTPUT.PUT_LINE('Country: ' || countryRecord.countryName || ', City: ' || cityRecord.cityName);
|
|
END LOOP;
|
|
END LOOP;
|
|
END;
|
|
/
|
|
|
|
DROP TABLE citiesTable;
|
|
|
|
DROP TABLE countriesTable;
|
|
----
|
|
|
|
|
|
=== Compliant solution
|
|
|
|
[source,sql]
|
|
----
|
|
SET SERVEROUTPUT ON
|
|
|
|
CREATE TABLE countriesTable(
|
|
countryName VARCHAR2(42)
|
|
);
|
|
|
|
CREATE TABLE citiesTable(
|
|
cityName VARCHAR2(42)
|
|
);
|
|
|
|
INSERT INTO countriesTable VALUES('India');
|
|
INSERT INTO countriesTable VALUES('Switzerland');
|
|
INSERT INTO countriesTable VALUES('United States');
|
|
|
|
INSERT INTO citiesTable VALUES('Berne');
|
|
INSERT INTO citiesTable VALUES('Delhi');
|
|
INSERT INTO citiesTable VALUES('Bangalore');
|
|
INSERT INTO citiesTable VALUES('New York');
|
|
|
|
BEGIN
|
|
FOR myRecord IN (SELECT * FROM countriesTable CROSS JOIN citiesTable) LOOP -- Compliant
|
|
DBMS_OUTPUT.PUT_LINE('Country: ' || myRecord.countryName || ', City: ' || myRecord.cityName);
|
|
END LOOP;
|
|
END;
|
|
/
|
|
|
|
DROP TABLE citiesTable;
|
|
|
|
DROP TABLE countriesTable;
|
|
----
|
|
|
|
ifdef::env-github,rspecator-view[]
|
|
|
|
'''
|
|
== Implementation Specification
|
|
(visible only on this page)
|
|
|
|
=== Message
|
|
|
|
Use a native join here rather than a nested PL/SQL cursor loop
|
|
|
|
|
|
endif::env-github,rspecator-view[]
|