Merge pull request #279 from green-code-initiative/ISSUE_239

green-code-initiative · Mar 17, 2024 · 1064c24 · 1064c24
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -9,6 +9,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- [#239](https://github.com/green-code-initiative/ecoCode/issues/239) Add new Java rule EC24 : Optimize Database SQL Queries (Clause LIMIT)
+
 ### Changed
 
 ### Deleted

diff --git a/RULES.md b/RULES.md
@@ -36,7 +36,7 @@ Some are applicable for different technologies.
 | EC12     | Modify several CSS properties all at once                     | ESLint key : @ecocode/no-multiple-style-changes /// type : Front-end                                                                                                                                                                                                                                                                                                                                                         |                                                                                                                                                                         | 🚫   | ❓   | ✅  | 🚫     | 🚫   | ❓  |
 | EC13     | Prefer API collections with pagination                        | ESLint key : @ecocode/prefer-collections-with-pagination /// type : Back-end                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                         | ❓    | ❓   | ✅  | ❓      | ❓    | ❓  |
 | EC22     | The use of methods for basic operations                       | Using methods for basic operations consumes additional system resources. The interpreter must in effect and solve the objects and then the methods, just to carry out these simple operations of the language.                                                                                                                                                                                                               | [cnumr best practices (3rd edition) BP_048 (no longer exists in edition 4)](https://www.greenit.fr/2019/05/07/ecoconception-web-les-115-bonnes-pratiques-3eme-edition/) | 🚫   | ✅   | 🚀 | 🚀     | 🚀   | 🚫 |
-| EC24     | Limit the number of returns for a SQL query                   | ESLint key : @ecocode/limit-db-query-results /// type : Back-end                                                                                                                                                                                                                                                                                                                                                             |                                                                                                                                                                         | 🚧   | 🚀  | ✅  | 🚀     | 🚀   | 🚀 |
+| EC24     | Limit the number of returns for a SQL query                   | ESLint key : @ecocode/limit-db-query-results /// type : Back-end                                                                                                                                                                                                                                                                                                                                                             |                                                                                                                                                                         | ✅    | 🚀  | ✅  | 🚀     | 🚀   | 🚀 |
 | EC25     | Do not use an image with empty source attribute               | ESLint key : @ecocode/no-empty-image-src-attribute /// type : Front-end                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                         | ❓    | ❓   | ✅  | ❓      | ❓    | ❓  |
 | EC26     | Prefer shorthand CSS notations                                | ESLint key : @ecocode/prefer-shorthand-css-notations /// type : Front-end                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                         | ❓    | ❓   | ✅  | ❓      | ❓    | ❓  |
 | EC27     | Usage of system.arraycopy to copy arrays                      | Programs spend most of the time in loops. These can be resource consuming, especially when they integrate heavy processing (IO access). Moreover, the size of the data and processing inside the loops will not allow full use of hardware mechanisms such as the cache or compiler optimization mechanisms.                                                                                                                 |                                                                                                                                                                         | ✅    | 🚫  | 🚫 | 🚫     | 🚫   | 🚫 |

diff --git a/ecocode-rules-specifications/src/main/rules/EC24/java/EC24.asciidoc b/ecocode-rules-specifications/src/main/rules/EC24/java/EC24.asciidoc
@@ -0,0 +1,40 @@
+:!sectids:
+
+== Why is this an issue?
+
+SQL queries often involve processing large amounts of data, and fetching a large number of rows can consume significant CPU resources.
+By limiting the number of rows returned, you reduce the amount of processing that needs to be done by the database engine, which in turn lowers CPU consumption.
+
+Transmitting a large number of rows over a network can be resource-intensive.
+By restricting the result set size, you reduce the amount of data that needs to be transferred between the database and the application, improving network efficiency.
+
+If you store data about customers, you certainly don’t need to retrieve information of all at once, because the larger the table will be, the more elements the query will return.
+
+[source,java,data-diff-id="1",data-diff-type="noncompliant"]
+----
+String sql = "SELECT user FROM myTable"; // Non-compliant
+----
+
+It may therefore be a good idea to limit the results and use pagination, for example.
+
+[source,java,data-diff-id="1",data-diff-type="compliant"]
+----
+String sql = "SELECT user FROM myTable LIMIT 50"; // Compliant
+----
+
+... and create an index like that ...
+[source,sql,data-diff-id="1",data-diff-type="compliant"]
+----
+CREATE INDEX idx_people_lastname_firstname ON people(lastname, firstname)
+----
+
+== Resources
+
+=== Documentation
+
+- https://dev.mysql.com/doc/refman/8.0/en/limit-optimization.html[MySQL Reference Manual] - LIMIT Query Optimization
+- https://www.postgresql.org/docs/current/queries-limit.html[PostgreSQL: Documentation] - LIMIT and OFFSET
+
+=== Articles & blog posts
+
+- https://www.oreilly.com/library/view/high-performance-mysql/9780596101718/ch04.html[Query Performance Optimization]