SQL查询具有许多联接的大量数据

Question

I have written a sql query for my requirement.
This is working fine for me. This is taking 0.0006 sec to execute.

I want to know from sql experts "will this work fine with large amount of data?".

I have written my query below.

SELECT HM_customers.id,
       HM_customers.username,
       HM_customers.firstname,
       HM_customers.lastname,
       HM_customers.company,
       HM_customers_address_bank.field_data
FROM   HM_orders
       JOIN HM_order_items
         ON HM_order_items.order_id = HM_orders.id
       JOIN HM_bid
         ON HM_order_items.bid_id = HM_bid.bid_id
       JOIN HM_customers
         ON HM_bid.user_id = HM_customers.id
       JOIN HM_customers_address_bank
         ON HM_customers_address_bank.id = HM_customers.default_billing_address
WHERE  HM_orders.id = '4' 

Any expert can advice me or let me know how can I improve this query. Please suggest me if any issue in this query.

NOTE:- This is a simple query. But I want to know, will this work with large amount of data with less time

Answer 1

You don't need to include the orders table:

SELECT c.id,
       c.username,
       c.firstname,
       c.lastname,
       c.company,
       cb.field_data
FROM   HM_order_items oi
       JOIN HM_bid b
         ON oi.bid_id = b.bid_id
       JOIN HM_customers c
         ON b.user_id = c.id
       JOIN HM_customers_address_bank cb
         ON cb.id = c.default_billing_address
WHERE  oi.order_id = '4'; 

Your query can also result in duplicate rows, if a customer bids on the same items multiple times. If you put in a select distinct , then you will incur overhead of duplicate elimination. If this becomes a problem, you will probably want to restructure the query as an exists .

Answer 2

There are few points worth noting

1) The reference to an outer table column in the WHERE clause prevents the OUTER JOIN from returning any non-matched rows, which implicitly converts the query to an INNER JOIN. This is probably a bug in the query or a misunderstanding of how OUTER JOIN works.

2) Selecting all columns with the * wildcard will cause the query's meaning and behavior to change if the table's schema changes, and might cause the query to retrieve too much data. You should only choose columns you need.

Answer 3

Please make your driven table to 'HM_customers' as all your data is coming from this table and change your join like this way, hopefully this will help you :)

SELECT hmCust.id,
       hmCust.username,
       hmCust.firstname,
       hmCust.lastname,
       hmCust.company,
       hmCustAdd.field_data
FROM   HM_customers hmCust
       INNER JOIN HM_bid hmBid
               ON hmBid.user_id = hmCust.id
       INNER JOIN HM_customers_address_bank hmCustAdd
               ON hmCustAdd.id = hmCust.default_billing_address
       INNER JOIN HM_order_items hmOrderItem
               ON hmOrderItem.order_id = hmBid.bid_id
       INNER JOIN HM_orders hmOrder
               ON hmOrder.id = hmOrderItem.order_id
WHERE  hmOrder.id = '4'