性能对复合sqlalchemy查询的顺序有影响吗? [英] Any performance impact to the order of a compound sqlalchemy query?

问题描述

我正在使用flask-sqlalchemy进行以下查询.两种方法都可以正常工作，但是我想知道，随着表的增加，以一种或另一种方式订购它是否会对性能产生影响:

I'm making the following query using flask-sqlalchemy. It works fine both ways, but I'm wondering, as my table grows, if there will be any performance impact to ordering it one way or another:

选项1:

things = Thing.query.filter(Thing.id != 5).order_by(Thing.id.desc()).limit(20).all()

选项2(互换了order_by和filter):

Option 2 (order_by and filter are swapped):

things = Thing.query.order_by(Thing.id.desc()).filter(Thing.id != 5).limit(20).all()

谢谢！

推荐答案

尽管SQL语法对形成语句的子句的顺序非常严格，但是SQLAlchemy中的ORM查询生成器是可生成的.它允许以更轻松的方式添加条件和选项，并且在执行之前对其进行编译以生成最终的SQL.因此，您的两个查询将导致相同的SQL，因此没有性能差异.

While SQL grammar is rather strict about the order of clauses that form a statement, the ORM query builder in SQLAlchemy is generative. It allows adding criteria and options in a more relaxed manner, and before execution it is compiled to produce the final SQL. In this light your two queries result in identical SQL, and so have no performance difference.

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