本文永久链接– https://tonybai.com/2024/07/20/sql-query-execution-orderSQL查询语句是关系数据库操作的核心。SQL查询语句有简有繁,简单的SQL查询语句,比如:SELECT column1, column2
FROM table_name
WHERE condition;对于这种查询语句,即便初学者也十分容易理解和掌握。但复杂的SQL查询语句,比如:SELECT department, AVG(salary) AS avg_salary
FROM employee_table
WHERE department IN ('IT', 'HR', 'Finance')
GROUP BY department
HAVING AVG(salary) > (SELECT AVG(salary) FROM employee_table)
ORDER BY avg_salary DESC
LIMIT 3;这种包含了SELECT、FROM、WHERE、GROUP BY、HAVING、ORDER BY和LIMIT等多个子句的复杂查询语句,即便是有多年开发经验的开发人员,如果不清楚各个子句的执行顺序,也很容易写错,并导致非预期的查询结果。关于SQL查询语句的执行顺序,互联网上有很多类似下面这样的速查表式(cheetsheet)的图:这
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