SQL JOIN查找没有特定值的匹配记录的记录 [英] SQL JOIN To Find Records That Don't Have a Matching Record With a Specific Value

问题描述

我正在尝试加快几年前为雇主的购买授权应用程序编写的代码.基本上，我有一个SLOW子查询，我想用JOIN替换(如果更快).

I'm trying to speed up some code that I wrote years ago for my employer's purchase authorization app. Basically I have a SLOW subquery that I'd like to replace with a JOIN (if it's faster).

当主管登录到应用程序时，他会看到他尚未授权或拒绝的购买请求列表.该列表是通过以下查询生成的:

When the director logs into the application he sees a list of purchase requests he has yet to authorize or deny. That list is generated with the following query:

SELECT * FROM SA_ORDER WHERE ORDER_ID NOT IN
    (SELECT ORDER_ID FROM SA_SIGNATURES WHERE TYPE = 'administrative director');

sa_order中只有大约900条记录，而sa_signature中只有1800条记录，该查询仍然需要大约5秒钟的时间来执行.我尝试使用LEFT JOIN检索我需要的记录，但是我只能获取sa_order中没有匹配记录的sa_order记录，并且我需要sa_order记录具有没有匹配记录的'行政主管'类型" ".非常感谢您的帮助！

There are only about 900 records in sa_order and 1800 records in sa_signature and this query still takes about 5 seconds to execute. I've tried using a LEFT JOIN to retrieve records I need, but I've only been able to get sa_order records with NO matching records in sa_signature, and I need sa_order records with "no matching records with a type of 'administrative director'". Your help is greatly appreciated!

两个表的架构如下:

涉及的表具有以下布局:

The tables involved have the following layout:

CREATE TABLE sa_order
(
    `order_id`        BIGINT       PRIMARY KEY AUTO_INCREMENT,
    `order_number`    BIGINT       NOT NULL,
    `submit_date`     DATE         NOT NULL,
    `vendor_id`       BIGINT       NOT NULL,
    `DENIED`          BOOLEAN      NOT NULL DEFAULT FALSE,
    `MEMO`            MEDIUMTEXT,
    `year_id`         BIGINT       NOT NULL,
    `advisor`         VARCHAR(255) NOT NULL,
    `deleted`         BOOLEAN      NOT NULL DEFAULT FALSE
);

CREATE TABLE sa_signature
(
    `signature_id`        BIGINT          PRIMARY KEY AUTO_INCREMENT,
    `order_id`            BIGINT          NOT NULL,
    `signature`           VARCHAR(255)    NOT NULL,
    `proxy`               BOOLEAN         NOT NULL DEFAULT FALSE,
    `timestamp`           TIMESTAMP       NOT NULL DEFAULT NOW(),
    `username`            VARCHAR(255)    NOT NULL,
    `type`                VARCHAR(255)    NOT NULL
);

推荐答案

在sa_signatures (type, order_id)上创建索引.

除非将sa_signatures允许为空，否则无需将查询转换为LEFT JOIN.使用索引，NOT IN也将执行.但是，以防万一您好奇:

This is not necessary to convert the query into a LEFT JOIN unless sa_signatures allows nulls in order_id. With the index, the NOT IN will perform as well. However, just in case you're curious:

SELECT  o.*
FROM    sa_order o
LEFT JOIN
        sa_signatures s
ON      s.order_id = o.order_id
        AND s.type = 'administrative director'
WHERE   s.type IS NULL

您应该从sa_signatures中选择一个NOT NULL列，以使WHERE子句表现良好.

You should pick a NOT NULL column from sa_signatures for the WHERE clause to perform well.

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