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

Question

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
);

Answer 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.

Answer 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/

Answer 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;

Answer 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