MySQL: Copy entire row from one to another and delete original - mysql

Could someone please explain (or point in right direction) how I would move multiple rows from one table to another and remove the row from the original table based on a set criteria?
I understand
INSERT INTO table2 SELECT * FROM table1
to copy the data from one table to another but I need to then remove the original. The reason being it has been suggested to speed up the querying of the table I should move all redundant data (ended, expired, products older than 3 months) from the main table to another one.
A bit of background, I have a table that holds products, some products have expired but the products still need to be accessible. There are about 50,000 products that have expired and 2,000 which are active. There is a status column (int 1 = active, 2 = expired etc) to determine what to show on the front end.
I guess this post is 2 questions:
Is there a better way to speed up the querying of the product table without removing expired items?
If not, how to move rows from one table to another
Many many thanks!

INSERT INTO table2 (column_name1, column_name2) SELECT column_name1,
column_name2 FROM table 1 WHERE (where clause here)
DELETE FROM table1 WHERE (where clause here)
Source for above: mysql move row between tables

50,000 records in the table really isn't that many. If you're having performance issues, I'd look at your queries and your indexes to help speed up performance. And since those expired records still need to be accessed, then it could be more difficult having multiple tables to maintain.
However, to move data from one table to another as you've asked, you just need to run 2 different statements. Assuming you want to move inactive products:
INSERT INTO ProductsBackup SELECT * FROM Products WHERE Status <> 1
DELETE FROM Products WHERE WHERE Status <> 1
If you have Identities on your columns, you might be better off specifying the column names. But assuming the ProductId is the Identity, then be careful moving those to a different table as you probably don't want to lose that original id as it may point to other tables.
Good luck.

Related

Best way to write SQL delete statement, deleting pairs of records

I have a MySQL database with just 1 table:
Fields are: blocknr (not unique), btcaddress (not unique), txid (not unique), vin, vinvoutnr, netvalue.
Indexes exist on both btcaddress and txid.
Data in it looks like this:
I need to delete all "deletable" record pairs. An example is given in red.
Conditions are:
txid must be the same (there can be more than 2 records with same txid)
vinvoutnr must be the same
vin must be different (can have only 2 values 0 and 1, so 1 must be 0 other must be 1)
In a table of 36M records, about 33M records will be deleted.
I've used this:
delete t1
from registration t1
inner join registration t2
where t1.txid=t2.txid and t1.vinvoutnr=t2.vinvoutnr and t1.vin<>t2.vin;
It works but takes 5 hours.
Maybe this would work too (not tested yet):
delete t1
from registration as t1, registration as t2
where t1.txid=t2.txid and t1.vinvoutnr=t2.vinvoutnr and t1.vin<>t2.vin;
Or do I forget about a delete query and try to make a new table with all non-delatables in and then drop the original ?
Database can be offline for this delete query.
Based on your question, you are deleting most of the rows in the table. That is just really expensive. A better approach is to empty the table and re-populate it:
create table temp_registration as
<query for the rows to keep here>;
truncate table registration;
insert into registration
select *
from temp_registration;
Your logic is a bit hard to follow, but I think the logic on the rows to keep is:
select r.*
from registration r
where not exists (select 1
from registration r2
where r2.txid = r.txid and
r2.vinvoutnr = r.vinvoutnr and
r2.vin <> r.vin
);
For best performance, you want an index on registration(txid, vinvoutnr, vin).
Given that you expect to remove the majority of your data it does sound like the simplest approach would be to create a new table with the correct data and then drop the original table as you suggest. Otherwise ADyson's corrections to the JOIN query might help to alleviate the performance issue.

how to structure large table and its transactions in database?

I have two big tables for example:
'tbl_items' and 'tbl_items_transactions'
First table keeping some items metadata which may have 20 (varchar) columns with millions rows... and second table keeping each transaction of first table.
for example if a user insert new record to tbl_items then automatically a new record will be adding to tbl_items_transactions with same data plus date, username and transaction type to keep each row history.
so in the above scenario two tables have same columns but tbl_items_transactions have 3 extra columns date, username, transaction_type to keep each tbl_items history
now assume we have 1000 users that wants to Insert, Update, Delete tbl_items records with a web application. so these two tables scale very soon (maybe billion rows in tbl_items_transactions)
I have tried MySQL, MariaDB, PostgreSQL... they are very good but when table scale and millions rows inserted they are slow when run some select queries on tbl_items_transactions... but sometimes PostgreSQL is faster than MySQL or MariaDB
now I think I'm doing wrong things... If you was me... do you use MariaDB or PostgreSQL or somthing like that and structure your database like what I did?
Your setup is wrong.
You should not duplicate the columns from tbl_items in tbl_items_transactions, rather you should have a foreign key in the latter table pointing to the former.
That way data integrity is preserved, and tbl_items_transactions will be much smaller. This technique is called normalization.
To speed up queries when the table get large, define indexes on them that match the WHERE and JOIN conditions.

Handling multiple MySql queries (Deleting and Copy)

Good morning.
I have a table on MySQL DataBase.
In this table there are 5 robots that can write like 10 record each per hour.
Every 3 month a script that I have created, make a copy of the table and then delete all the table entries (In this way I can keep the IDs in a certain order).
My question is.
That are two different statement:
CREATE TABLE omologationResult_{date} AS SELECT * FROM omologationResult
DELETE FROM omologationResult
if the script is going to copy the table at point 0, and a record will be added from the robots, there's no problem, because the SQL statement starts from the lowest ID 'till the end. But if the script is going to delete the table and the robot is writing in it. What will happen? I lose the last robot record?
And if it's true. What can I do to make a copy of the table and then remove only the data that I've copied?
Thank you
Yes, this is not a safe operation because it's not atomic. It's quite possible for another thread to insert values into that table in between your CREATE .. SELECT and the DELETE. One option you have is to use a multi table DELETE
CREATE TABLE omologationResult_{date} AS SELECT * FROM omologationResult;
DELETE omologationResult FROM omologationResult
INNER JOIN omologationResult_{date} ON omologationResult_{date}.id = omologationResult.id
Will ensure that only items that exist in both tables have been deleted from omologationResult

MySQL combine n tables

I have n (source) tables with the same structure that each have few million rows. Each of these table receives new data from different sources on a regular basis.
(Ex: Sales table. Each store have its own sales table. There's 1000 stores selling hundred of thousands items each day. How would you combine those tables?)
I would like to merge them in one summary table. I would like the changes from any of the source tables to be reflected on the summary and changes on the summary to be reflected on the appropriate source table.
(Ex: Sales table. When new sales occurs, the summary table is updated. If a changes to the sale is made in the summary table, it is reflected on the appropriate store table.)
I can see three solutions.
1.Create an event/trigger that would refresh my summary tables at a given time or after an insert/update/delete.
Something like:
#Some event triggers this
DROP TABLE table_summary;
INSERT INTO table_summary
SELECT * FROM table1
UNION ALL
SELECT * FROM table2
UNION ALL
SELECT * FROM tablen...
The downside here, I believe, is performance, I do not think I can afford to run this query every time there is an INSERT/UPDATE/DELETE on one of the table.
2.Create a view.
CREATE VIEW table_summary AS
SELECT * FROM table1
UNION ALL
SELECT * FROM table2;
#This query takes 90s to complete
Performance wise, I have the same kind of problem as with the solution #1
3.Create an INSERT/UPDATE/DELETE trigger for each table. That's a lot of triggers and MySQL limit to one per table. I started that way but the code scaffolding to maintain appears impressive and likely hard to maintain.
I am sure there's a better way I have not think of.

Index counter shared by multiple tables in mysql

I have two tables, each one has a primary ID column as key. I want the two tables to share one increasing key counter.
For example, when the two tables are empty, and counter = 1. When record A is about to be inserted to table 1, its ID will be 1 and the counter will be increased to 2. When record B is about to be inserted to table 2, its ID will be 2 and the counter will be increased to 3. When record C is about to be inserted to table 1 again, its ID will be 3 and so on.
I am using PHP as the outside language. Now I have two options:
Keep the counter in the database as a single-row-single-column table. But every time I add things to table A or B, I need to update this counter table.
I can keep the counter as a global variable in PHP. But then I need to initialize the counter from the maximum key of the two tables at the start of apache, which I have no idea how to do.
Any suggestion for this?
The background is, I want to display a mix of records from the two tables in either ASC or DESC order of the creation time of the records. Furthermore, the records will be displayed in page-style, say, 50 records per page. Records are only added to the database rather than being removed. Following my above implementation, I can just perform a "select ... where key between 1 and 50" from two tables and merge the select datasets together, sort the 50 records according to IDs and display them.
Is there any other idea of implementing this requirement?
Thank you very much
Well, you will gain next to nothing with this setup; if you just keep the datetime of the insert you can easily do
SELECT * FROM
(
SELECT columnA, columnB, inserttime
FROM table1
UNION ALL
SELECT columnA, columnB, inserttime
FROM table2
)
ORDER BY inserttime
LIMIT 1, 50
And it will perform decently.
Alternatively (if chasing last drop of preformance), if you are merging the results it can be an indicator to merge the tables (why have two tables anyway if you are merging the results).
Or do it as SQL subclass (then you can have one table maintain IDs and other common attributes, and the other two reference the common ID sequence as foreign key).
if you need creatin time wont it be easier to add a timestamp field to your db and sort them according to that field?
i believe using ids as a refrence of creation is bad practice.
If you really must do this, there is a way. Create a one-row, one-column table to hold the last-used row number, and set it to zero. On each of your two data tables, create an AFTER INSERT trigger to read that table, increment it, and set the newly-inserted row number to that value. I can't remember the exact syntax because I haven't created a trigger for years; see here http://dev.mysql.com/doc/refman/5.0/en/triggers.html