SQL JOIN To Find Records That Don't Have a Matching Record With a Specific Value

问题

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).

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');

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!

The schema for the two tables is as follows:

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
);

回答1:

Create an index on sa_signatures (type, order_id).

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

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

回答2:

You could replace the [NOT] IN operator with EXISTS for faster performance.

So you'll have:

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

Reason : "When using “NOT IN”, the query performs nested full table scans, whereas for “NOT EXISTS”, query can use an index within the sub-query."

Source : http://decipherinfosys.wordpress.com/2007/01/21/32/

回答3:

This following query should work, however I suspect your real issue is you don't have the proper indices in place. You should have an index on the SA_SGINATURES table on the ORDER_ID column.

SELECT * 
FROM 
SA_ORDER 
LEFT JOIN
SA_SIGNATURES
ON
SA_ORDER.ORDER_ID = SA_SIGNATURES.ORDER_ID AND
TYPE = 'administrative director'
WHERE 
SA_SIGNATURES.ORDER_ID IS NULL;

回答4:

select * from sa_order as o inner join sa_signature as s on o.orderid = sa.orderid and sa.type = 'administrative director'

also, you can create a non clustered index on type in sa_signature table

even better - have a master table for types with typeid and typename, and then instead of saving type as text in your sa_signature table, simply save type as integer. thats because computing on integers is way faster than computing on text

来源：https://stackoverflow.com/questions/4853203/sql-join-to-find-records-that-dont-have-a-matching-record-with-a-specific-value

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sql

mysql

join

subquery