Understanding how SQL queries are processed can greatly boost your ability to optimize and write efficient queries. So, let’s break it down together! 🚀
📌 SQL query execution follows a specific order, known as the logical query processing order.
Here’s a simplified breakdown of the steps involved:
1️⃣ FROM: The FROM clause specifies the tables or views involved in the query. It’s where the data comes from.
2️⃣ WHERE: The WHERE clause filters the data from the source specified in the FROM clause based on conditions. It narrows down the dataset.
3️⃣ GROUP BY: The GROUP BY clause groups the filtered data based on specified columns. This step is useful for aggregating data using functions like SUM, COUNT, or AVG.
4️⃣ HAVING: The HAVING clause filters the grouped data based on conditions. It works like the WHERE clause but operates on grouped data.
5️⃣ SELECT: The SELECT clause selects the columns to include in the result set. It can include aggregations and expressions based on grouped and filtered data.
6️⃣ ORDER BY: The ORDER BY clause sorts the result set based on specified columns or expressions. It determines the final order of the returned rows.
7️⃣ LIMIT/OFFSET: The LIMIT/OFFSET clause is optional and helps restrict the number of rows returned or implement pagination.
💡 Remember, the logical query processing order may not always match the physical execution order. The database optimizer decides the most efficient way to execute the query, using techniques like query rewriting or parallel processing.
🔀 Understanding the logical query processing order empowers you to write optimized queries by placing conditions and aggregations strategically. It also helps interpret query results and troubleshoot performance issues.
Happy Learning! Check the best resources to learn SQL-> 8 Best SQL Courses on Coursera You Must Know in 2023, https://www.mltut.com/best-sql-courses-on-coursera/
了解SQL查询的处理方式可以极大地提高您优化和编写高效查询的能力。那么，让我们一起来分解吧！ 🚀
📌 SQL查询执行遵循特定顺序，称为逻辑查询处理顺序。
以下是所涉及步骤的简化分解：
1️⃣ FROM：FROM子句指定查询涉及的表或视图。这是数据的来源。
2️⃣ WHERE：WHERE子句根据条件从FROM子句指定的源中过滤数据。它缩小了数据集。
3️⃣ GROUP BY：GROUP BY子句根据指定的列对过滤后的数据进行分组。此步骤对于使用 SUM、COUNT或AVG等函数聚合数据很有用。
4️⃣ HAVING：HAVING子句根据条件过滤分组数据。它的工作方式类似于 WHERE 子句，但对分组数据进行操作。
5️⃣ SELECT：SELECT子句选择要包含在结果集中的列。它可以包括基于分组和过滤数据的聚合和表达式。
6️⃣ ORDER BY：ORDER BY子句根据指定的列或表达式对结果集进行排序。它确定返回行的最终顺序。
7️⃣ LIMIT/OFFSET：LIMIT/OFFSET子句是可选的，有助于限制返回的行数或实现分页。
💡 请记住，逻辑查询处理顺序可能并不总是与物理执行顺序匹配。数据库优化器使用查询重写或并行处理等技术来决定执行查询的最有效方式。
🔀 了解逻辑查询处理顺序使您能够通过策略性地放置条件和聚合来编写优化的查询。它还有助于解释查询结果和解决性能问题。
快乐学习！查看学习SQL的最佳资源-> 《2023年你必须知道的Coursera上8门最佳SQL课程》，https://www.mltut.com/best-sql-courses-on-coursera/
Share & Translate: Chinou Gea (秦陇纪) @2023 DSS-SDS, IFS-AHSC. Data Simplicity Community Facebook Group https://m.facebook.com/groups/290760182638656/ #DataSimp #DataScience #DataComputing #computer #program #AI #ArtificialIntelligence #SQL #Database #QueryOptimization #DataAnalysis #execute.