MySQL Select Query running very slow - mysql

Question

I have a MySQL query that works but is very slow. I am guessing due to the amount of joins.
SELECT
order_header.order_head_id,
order_header.order_date,
order_header.status,
suppliers.supplier,
categories.category,
order_header.user,
order_header.sage_ref,
SUM(order_lines.total_price) AS price
FROM
order_header
LEFT JOIN
order_lines ON order_header.order_head_id = order_lines.order_head_id
LEFT JOIN
suppliers ON order_header.supplier_id = suppliers.supp_id
LEFT JOIN
categories ON order_header.category = categories.cat_id
WHERE
order_header.status LIKE '%'
AND order_header.order_head_id LIKE '%'
AND order_header.user LIKE '%'
GROUP BY order_header.order_head_id
ORDER BY order_head_id DESC
LIMIT 50;
Results of the EXPLAIN query
SHOW CREATE TABLE results
CREATE TABLE `categories` (
`cat_id` int(11) NOT NULL AUTO_INCREMENT,
`category` varchar(45) DEFAULT NULL,
`status` varchar(45) DEFAULT NULL,
PRIMARY KEY (`cat_id`)
) ENGINE=InnoDB AUTO_INCREMENT=63 DEFAULT CHARSET=latin1
CREATE TABLE `order_header` (
`order_head_id` int(11) NOT NULL AUTO_INCREMENT,
`status` varchar(45) DEFAULT NULL,
`category` varchar(45) NOT NULL,
`order_date` date DEFAULT NULL,
`supplier_id` varchar(45) NOT NULL,
`user` varchar(45) DEFAULT NULL,
`sage_ref` varchar(45) DEFAULT NULL,
`query_notes` varchar(500) DEFAULT NULL,
PRIMARY KEY (`order_head_id`)
) ENGINE=InnoDB AUTO_INCREMENT=2249 DEFAULT CHARSET=latin1
CREATE TABLE `order_lines` (
`order_lines_id` int(11) NOT NULL AUTO_INCREMENT,
`order_head_id` int(11) DEFAULT NULL,
`qty` int(11) DEFAULT NULL,
`description` varchar(255) DEFAULT NULL,
`unit_price` decimal(65,2) DEFAULT NULL,
`total_price` decimal(65,2) DEFAULT NULL,
PRIMARY KEY (`order_lines_id`)
) ENGINE=InnoDB AUTO_INCREMENT=3981 DEFAULT CHARSET=latin1
CREATE TABLE `suppliers` (
`supp_id` int(11) NOT NULL AUTO_INCREMENT,
`supplier` varchar(255) DEFAULT NULL,
`status` varchar(225) DEFAULT NULL,
PRIMARY KEY (`supp_id`)
) ENGINE=InnoDB AUTO_INCREMENT=161 DEFAULT CHARSET=latin1
SQL Version 5.6.30
I am not great on MySQL and was wondering if anyone can see a way to improve the query so that it runs quicker.
Your help would be gratefully appreciated.
Many thanks,
John

Answer 1

It can make sense to wrap the first (left) join into a GROUP BY subquery. GROUP BY and LIMIT will limit the number of row which will be used in the following two joins:
SELECT
x.order_head_id,
x.order_date,
x.status,
suppliers.supplier,
categories.category,
x.user,
x.sage_ref,
x.price
FROM (
SELECT
order_header.supplier_id,
order_header.category,
order_header.order_head_id,
order_header.order_date,
order_header.status,
order_header.user,
order_header.sage_ref,
SUM(order_lines.total_price) AS price
FROM order_header
LEFT JOIN order_lines ON order_header.order_head_id = order_lines.order_head_id
WHERE order_header.status LIKE '%'
AND order_header.order_head_id LIKE '%'
AND order_header.user LIKE '%'
GROUP BY order_header.order_head_id
ORDER BY order_head_id DESC
LIMIT 50
) x
LEFT JOIN suppliers ON x.supplier_id = suppliers.supp_id
LEFT JOIN categories ON x.category = categories.cat_id
ORDER BY order_head_id DESC