84 lines
2.1 KiB
Plaintext
84 lines
2.1 KiB
Plaintext
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.
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== Noncompliant Code Example
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----
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SET SERVEROUTPUT ON
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CREATE TABLE countriesTable(
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countryName VARCHAR2(42)
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);
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CREATE TABLE citiesTable(
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cityName VARCHAR2(42)
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);
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INSERT INTO countriesTable VALUES('India');
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INSERT INTO countriesTable VALUES('Switzerland');
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INSERT INTO countriesTable VALUES('United States');
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INSERT INTO citiesTable VALUES('Berne');
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INSERT INTO citiesTable VALUES('Delhi');
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INSERT INTO citiesTable VALUES('Bangalore');
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INSERT INTO citiesTable VALUES('New York');
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BEGIN
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FOR countryRecord IN (SELECT countryName FROM countriesTable) LOOP
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FOR cityRecord IN (SELECT cityName FROM citiesTable) LOOP -- Non-Compliant
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DBMS_OUTPUT.PUT_LINE('Country: ' || countryRecord.countryName || ', City: ' || cityRecord.cityName);
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END LOOP;
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END LOOP;
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END;
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/
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DROP TABLE citiesTable;
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DROP TABLE countriesTable;
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----
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== Compliant Solution
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----
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SET SERVEROUTPUT ON
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CREATE TABLE countriesTable(
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countryName VARCHAR2(42)
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);
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CREATE TABLE citiesTable(
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cityName VARCHAR2(42)
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);
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INSERT INTO countriesTable VALUES('India');
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INSERT INTO countriesTable VALUES('Switzerland');
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INSERT INTO countriesTable VALUES('United States');
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INSERT INTO citiesTable VALUES('Berne');
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INSERT INTO citiesTable VALUES('Delhi');
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INSERT INTO citiesTable VALUES('Bangalore');
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INSERT INTO citiesTable VALUES('New York');
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BEGIN
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FOR myRecord IN (SELECT * FROM countriesTable CROSS JOIN citiesTable) LOOP -- Compliant
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DBMS_OUTPUT.PUT_LINE('Country: ' || myRecord.countryName || ', City: ' || myRecord.cityName);
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END LOOP;
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END;
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/
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DROP TABLE citiesTable;
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DROP TABLE countriesTable;
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----
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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include::message.adoc[]
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endif::env-github,rspecator-view[]
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