Left or Inner Join and condition at subquery

你的查询目标是从 shipment 表中获取与 distance 表关联的数据，并筛选出里程数超过 3000 的记录，同时按 shipment_id 排序。这是一个典型的查询场景，可以通过以下方式改进性能或提高可读性： 原查询 SELECT *FROM shipmentLEFT JOIN distanceON (shipment.origin = distance.origin)AND (shipment.destination = distance.destination)WHERE distance.miles > 3000ORDER BY shipment_id; 方法 1：使用 INNER JOIN SELECT shipment.*, distance.milesFROM shipmentINNER JOIN distanceON shipment.origin = distance.originAND shipment.destination = distance.destinationWHERE distance.miles > 3000ORDER BY shipment.shipment_id; 适用场景： 数据量适中，无需提前过滤 distance 表。 只需简单的等值连接即可满足需求。 方法 2：将筛选条件提前（推荐） SELECT… Read More

SQL 条件 in 的优化

原查询 SELECT DISTINCT(class)FROM shipWHERE manufacturer_id IN (SELECT manufacturer_idFROM manufacturerWHERE state = ‘CA’); 改进方法 方法 1：使用 JOIN 提高可读性 通过 JOIN 重写查询，可以让逻辑更清晰： SELECT DISTINCT(ship.class)FROM shipJOIN manufacturerON ship.manufacturer_id = manufacturer.manufacturer_idWHERE manufacturer.state = ‘CA’; 优点： JOIN 的写法更直观，特别是当数据表之间关系明确时。 一些数据库管理系统（如 MySQL）对 JOIN 的性能优化可能优于子查询。 方法 2：避免 DISTINCT（如果可能） 如果确定每个 manufacturer_id 对应唯一的 class，可以省略 DISTINCT，提高查询效率： SELECT ship.classFROM shipJOIN manufacturerON ship.manufacturer_id = manufacturer.manufacturer_idWHERE manufacturer.state = ‘CA’;… Read More

Microsoft Access Performance Tips to Speed up Your Access Databases

Over 100 Tips for Faster Microsoft Access Databases This paper outlines specific performance tips you can use to improve the speed of your Microsoft Access applications. These tips apply to all versions of Access including Access 2016, 2013, 2010, 2007, 2003, 2002, 2000, and 97. Some of the tips may contradict each other but they… Read More

How to shut down a custom Access application remotely

Summary Sometimes, you may have to perform maintenance tasks on a Microsoft Access database, such as compacting or repairing, making backup copies, or making design modifications. Many of these operations require that all users exit the database. However, there is no built in way to force users to quit Microsoft Access. And it is not… Read More

7 Ways To Do Sequential Numbering in Microsoft Access

Occasionally we come across project requirements that include the ability to do sequential numbering in Access on a set of data. We cannot just use the auto-number data type because there is no promise of sequentiality but only uniqueness. In other words, if someone creates a record then later deletes it, there will be a… Read More