Struggling with a large dataset in my mariaDB database. I have two tables, where table A contains 57 million rows and table B contains around 500. Table B is a subset of ids related to a column in table A. I want to delete all rows from A which do not have a corresponding ID in table B.
Example table A:
classification_id
Name
20
Mercedes
30
Kawasaki
80
Leitz
70
HP
Example table B:
classification_id
Type
20
car
30
bike
40
bus
50
boat
So in this example the last two rows from table A would be deleted (or a mirror table would be made containing only the first two rows, thats also fine).
I tried to do the second one using an inner join but this query took a few minutes before giving an out of memory exception.
Any suggestions on how to tackle this?
try this:
delete from "table A" where classification_id not in (select classification_id from "table B");
Since you say that the filter table contains a relatively small number of rows, your best bet would be creating a separate table that contains the same columns as the original table A and the rows that match your criteria, then replace the original table and drop it. Also, with this number of IDs you probably want to use WHERE IN () instead of joins - as long as the field you're using there is indexed, it will usually be way faster. Bringing it all together:
CREATE TABLE new_A AS
SELECT A.* FROM A
WHERE classification_id IN (SELECT classification_id FROM B);
RENAME TABLE A TO old_A, new_A to A;
DROP TABLE old_A;
Things to be aware of:
Backup your data! And test the queries thoroughly before running that DROP TABLE. You don't want to lose 57M rows of data because of a random answer at StackOverflow.
If A has any indexes or foreign keys, these won't be copied over - so you'll have to recreate them all manually. I'd recommend running SHOW CREATE TABLE A first and making note on its structure. Alternatively, you may consider creating the table new_A explicitly using the output of SHOW CREATE TABLE A as a template and then performing INSERT INTO new_A SELECT ... instead of CREATE TABLE new_A AS SELECT ... with the same query after this.
I have created a new column in the "destination" table with the same name, datatype and other values as appear in the "source" column in a different table. I have tried many suggested solutions as found on stackoverflow. This one appeared to work (found on Quora) but when I went to the destination table the previously empty column remains empty with nothing but NULL values noted. This is the Quora suggestion:
you can fill data in column from another existing one by using INSERT INTO statement and SELECT statement together like that
INSERT INTO `table1`(column_name)
SELECT column_name FROM `table2`
here you filled a single column in table 1 with data located in a single column in table 2
so if you want to fill the whole table 1 (all columns) with data located in table 2 you can make table 1 like a copy of table 2 by using the same code but without column name
INSERT INTO `table1`
SELECT * FROM `table2`
but note to do this (copy table content to another one) ensure that both of tables have the same column count and data types.
I'm not sure what is meant by column count (do the two table have to have the same number of columns?)
When I run it I get error # 1138.
Any help greatly appreciated. -JG
I have to import loads of files into a database, the problem is, with time it got more columns.
The files are all insert-lines from SQLite, but i need them in MySQL, SQLIte doesn't provide column-names in their sql files, so the MySQL-script crashes when there are more or less columns as in the insert statement.
Is there a solution for this? Maybe over a join?
The new added columns are in the end, so the first are ALWAYS the same.
Is there any possibility to insert the sql-file in a temporary table, then make a join on an empty table (or 1 ghost record) to get the right amount of columns, and then do a insert on each line from that table to the table i want to have the data in?
Files looks like:
INSERT into theTable Values (1,1,Text,2913, txt,);
And if columns were added the file is like
INSERT into theTable Values (1,1,Text,2913, txt,added-Text);
When I imported a table with 30 million rows from a text file to a MYSQL table it only took 1 minute. However, I realized that I missed a column and that I needed to add it to the table. From the MYSQL command line, I wrote the following command:
create tableC as(tableA.T1, tableB.ZID from tableA, table B where A.ZID = B.ZID)
It's been over one hour and the command has not terminated. Does anyone know the reason why? TableB was already in the MYSQL server.
Not 100% sure but you might be better off altering the table first and adding the column, then doing an update to populate that column
ALTER TABLE tableB ADD COLUMN colA yourColumnDefinition;
UPDATE tableB SET colA = <however you do it>;
I'm not totally sure which table you are adding the column to or how you are computing it. Based on the query you posted it looks like you are creating a mapping table to map two table's IDs to each other. If that is the case you would probably be better off putting a foreign key in one of the tables.
Again, this might not be exactly what you are looking for but if you just want to add a column to a table you already created this might be a better approach.
I got a table with a normal setup of auto inc. ids. Some of the rows have been deleted so the ID list could look something like this:
(1, 2, 3, 5, 8, ...)
Then, from another source (Edit: Another source = NOT in a database) I have this array:
(1, 3, 4, 5, 7, 8)
I'm looking for a query I can use on the database to get the list of ID:s NOT in the table from the array I have. Which would be:
(4, 7)
Does such exist? My solution right now is either creating a temporary table so the command "WHERE table.id IS NULL" works, or probably worse, using the PHP function array_diff to see what's missing after having retrieved all the ids from table.
Since the list of ids are closing in on millions or rows I'm eager to find the best solution.
Thank you!
/Thomas
Edit 2:
My main application is a rather easy table which is populated by a lot of rows. This application is administrated using a browser and I'm using PHP as the intepreter for the code.
Everything in this table is to be exported to another system (which is 3rd party product) and there's yet no way of doing this besides manually using the import function in that program. There's also possible to insert new rows in the other system, although the agreed routing is to never ever do this.
The problem is then that my system cannot be 100 % sure that the user did everything correct from when he/she pressed the "export" key. Or, that no rows has ever been created in the other system.
From the other system I can get a CSV-file out where all the rows that system has. So, by comparing the CSV file and my table I can see if:
* There are any rows missing in the other system that should have been imported
* If someone has created rows in the other system
The problem isn't "solving it". It's making the best solution to is since there are so much data in the rows.
Thanks again!
/Thomas
We can use MYSQL not in option.
SELECT id
FROM table_one
WHERE id NOT IN ( SELECT id FROM table_two )
Edited
If you are getting the source from a csv file then you can simply have to put these values directly like:
I am assuming that the CSV are like 1,2,3,...,n
SELECT id
FROM table_one
WHERE id NOT IN ( 1,2,3,...,n );
EDIT 2
Or If you want to select the other way around then you can use mysqlimport to import data in temporary table in MySQL Database and retrieve the result and delete the table.
Like:
Create table
CREATE TABLE my_temp_table(
ids INT,
);
load .csv file
LOAD DATA LOCAL INFILE 'yourIDs.csv' INTO TABLE my_temp_table
FIELDS TERMINATED BY ','
LINES TERMINATED BY '\n'
(ids);
Selecting records
SELECT ids FROM my_temp_table
WHERE ids NOT IN ( SELECT id FROM table_one )
dropping table
DROP TABLE IF EXISTS my_temp_table
What about using a left join ; something like this :
select second_table.id
from second_table
left join first_table on first_table.id = second_table.id
where first_table.is is null
You could also go with a sub-query ; depending on the situation, it might, or might not, be faster, though :
select second_table.id
from second_table
where second_table.id not in (
select first_table.id
from first_table
)
Or with a not exists :
select second_table.id
from second_table
where not exists (
select 1
from first_table
where first_table.id = second_table.id
)
The function you are looking for is NOT IN (an alias for <> ALL)
The MYSQL documentation:
http://dev.mysql.com/doc/refman/5.0/en/all-subqueries.html
An Example of its use:
http://www.roseindia.net/sql/mysql-example/not-in.shtml
Enjoy!
The problem is that T1 could have a million rows or ten million rows, and that number could change, so you don't know how many rows your comparison table, T2, the one that has no gaps, should have, for doing a WHERE NOT EXISTS or a LEFT JOIN testing for NULL.
But the question is, why do you care if there are missing values? I submit that, when an application is properly architected, it should not matter if there are gaps in an autoincrementing key sequence. Even an application where gaps do matter, such as a check-register, should not be using an autoincrenting primary key as a synonym for the check number.
Care to elaborate on your application requirement?
OK, I've read your edits/elaboration. Syncrhonizing two databases where the second is not supposed to insert any new rows, but might do so, sounds like a problem waiting to happen.
Neither approach suggested above (WHERE NOT EXISTS or LEFT JOIN) is air-tight and neither is a way to guarantee logical integrity between the two systems. They will not let you know which system created a row in situations where both tables contain a row with the same id. You're focusing on gaps now, but another problem is duplicate ids.
For example, if both tables have a row with id 13887, you cannot assume that database1 created the row. It could have been inserted into database2, and then database1 could insert a new row using that same id. You would have to compare all column values to ascertain that the rows are the same or not.
I'd suggest therefore that you also explore GUID as a replacement for autoincrementing integers. You cannot prevent database2 from inserting rows, but at least with GUIDs you won't run into a problem where the second database has inserted a row and assigned it a primary key value that your first database might also use, resulting in two different rows with the same id. CreationDateTime and LastUpdateDateTime columns would also be useful.
However, a proper solution, if it is available to you, is to maintain just one database and give users remote access to it, for example, via a web interface. That would eliminate the mess and complication of replication/synchronization issues.
If a remote-access web-interface is not feasible, perhaps you could make one of the databases read-only? Or does database2 have to make updates to the rows? Perhaps you could deny insert privilege? What database engine are you using?
I have the same problem: I have a list of values from the user, and I want to find the subset that does not exist in anther table. I did it in oracle by building a pseudo-table in the select statement Here's a way to do it in Oracle. Try it in MySQL without the "from dual":
-- find ids from user (1,2,3) that *don't* exist in my person table
-- build a pseudo table and join it with my person table
select pseudo.id from (
select '1' as id from dual
union select '2' as id from dual
union select '3' as id from dual
) pseudo
left join person
on person.person_id = pseudo.id
where person.person_id is null