mysql query takes about a minute using between - mysql

Question

I have a query that joins four table but I can't understand why its taking about a minute. I know the date between is more than 3 years. I don't really know what to do and how to optimize this query for better performance. Can someone give me suggestion on what to do? Will attached the query and the explain of the query.
SELECT
`purchase_order`.`id`,
`customer`.`name` AS customer_name,
`purchase_order`.`po_date`,
`purchase_order`.`po_number`,
`purchase_order`.`customer_id` AS customer_id ,
`customer`.`name` AS customer_name,
`purchase_order`.`status` AS po_status,
`purchase_order_items`.`product_id`,
`purchase_order_items`.`po_item_name`,
`product`.`weight` as product_weight,
`product`.`pending` as product_pending,
`product`.`company_owner` as company_owner,
`purchase_order_items`.`uom`,
`purchase_order_items`.`po_item_type`,
`purchase_order_items`.`order_sequence`,
`purchase_order_items`.`pending_balance`,
`purchase_order_items`.`quantity`,
`purchase_order_items`.`notes`,
`purchase_order_items`.`status` AS po_item_status,
`purchase_order_items`.`id` AS po_item_id
FROM purchase_order
INNER JOIN customer ON `customer`.`id` = `purchase_order`.`customer_id`
INNER JOIN purchase_order_items ON `purchase_order_items`.`po_id` = `purchase_order`.`id`
INNER JOIN product ON `purchase_order_items`.`product_id` = `product`.`id` WHERE
`purchase_order_items`.`product_id` = '121' AND
`purchase_order`.`po_date`
BETWEEN '2016-01-01' AND '2019-02-28' AND
`purchase_order_items`.`status` IN('Pending','Incomplete')
ORDER BY `purchase_order`.`po_date` DESC LIMIT 0, 20
Im also not sure what to do about the explain and Im still trying to understand why its like this and how can i optimize the query. I hope someone could help me on this.

Answer 1

It looks like your query is good. Rewritten using alias names for tables for shorter yet still readable "po" vs "purchase_order", "poi" vs "purchase_order_items"
Your purchase_order table should have an index at a minimum on date THEN id. So your WHERE clause can optimize based on the date, but also have the po.id as a basis to JOIN to your purchase order items table by id.
Next, the purchase order items, would help with an index on ( po_id, product_id, status ) to help optimize that join criteria.
Purchase_Order index (po_date, id )
Purchase_Order_Items index ( po_id, product_id, status )
SELECT
po.id,
c.name AS customer_name,
po.po_date,
po.po_number,
po.customer_id AS customer_id ,
c.name AS customer_name,
po.status AS po_status,
poi.product_id,
poi.po_item_name,
p.weight as product_weight,
p.pending as product_pending,
p.company_owner as company_owner,
poi.uom,
poi.po_item_type,
poi.order_sequence,
poi.pending_balance,
poi.quantity,
poi.notes,
poi.status AS po_item_status,
poi.id AS po_item_id
FROM
purchase_order po
INNER JOIN customer c
ON po.customer_id = c.id
INNER JOIN purchase_order_items poi
ON po.id = poi.po_id
AND poi.product_id = '121'
AND poi.status IN ('Pending','Incomplete')
INNER JOIN product p
ON poi.product_id = p.id
WHERE
po.po_date BETWEEN '2016-01-01' AND '2019-02-28'
ORDER BY
po.po_date DESC
LIMIT
0, 20
If that doesn't help, Your order of tables appears ok but the engine might be trying to think too much for you. You can try adding additional keyword "STRAIGHT_JOIN" (specific to mysql).
select STRAIGHT_JOIN ( ... rest of query )
This tells mySQL to run the query in the table order I gave you.