Maybe my way of thought is wrong, so first off I will try to explain the situation in words.
I have a Database with about 40000 Titles, some of them are related to each other. This Relations are saved in a different database in a simple a b type manner. The problem is that the system was changed so there is a special row in the main database which contains the old id. And the b value is also the old id... However now I want to replace the b value with the new auto increment id given by the database for all the entries in the relations table. So I thought that I need to create a new table, copy the contents but replacing the b value with the new id...
CREATE TABLE list_relations_new LIKE list_listitem_relations;
INSERT list_relations_new
SELECT lr.a, li.id, lr.typeID
FROM list_listitems li
LEFT JOIN list_listitem_relations lr
ON li.oldID = lr.b
Executing this query doesn't give any errors, but also doesn't even create a new table? I hope somebody can help me to sort this out...
Related
One of our tables has been maligned
/*edit as per commented request
On doing an update to a specific column I accidentally neglected to specify for which row I wish to make this change and set the offending value for every row in the table.
*/end edit
but we have a very recent backup, however not so recent that other tables won't lose data if we do a total database restore.
I'm wondering what the procedure is (assuming there is one) of copying the contents of a given table from one database to another.
The largest problem is that I can't just drop the offending table and replace it as it has rows that are indexed by id into other tables. This won't be a problem if we just take the values from the identical rows in the back-up and bring them over (since the row ids wouldn't change).
It's unclear what exactly has gone wrong with your data. But I'm thinking maybe just a column or two has got messed up. As you said, you just want to copy over the data from the old table, based on the id column.
Assuming you've imported the backup database as "olddb" and the current one is named "newdb":
UPDATE newdb.yourtable newtable, olddb.yourtable oldtable
SET newtable.somecolumn = oldtable.somecolumn
WHERE newtable.id = oldtable.id
Use mysqldatadump for that particular table, and then feed that into the other database.
You can edit the dump file prior to redaing it in to the target table.
See: https://dba.stackexchange.com/questions/9306/how-do-you-mysqldump-specific-tables
Is there a way in Access to link two variables together across separate tables?
Ex. I have one variable in table A that says Consent1 was signed.
Table B will be a summary table showing which consents are needed. In other words, If Consent1 was signed in table A, table B will show Consent1 is NOT NEEDED.
You could build a trigger to update Table B, but if your database is normalized properly there's no need to do that. Just build a query that does the same thing. Join Table A to Table B linked on whatever common field they have (I can't tell you exactly how to do that since you've offered no table structure), and then add a field to the query that looks something like this:
Consent: IIF([Table A].Consent = "Signed", "Not Needed", "Needed")
I have two tables with some same fields like:
Table A: fname, lname, address, age, email, mobile, website, blog
Table B: fname, lname, address, age, email
Both these tables are used by different modules on my website. I want to sync the first five fields of both tables in such a way that whenever a new row is added or an existing row is modified in Table A, the Table B is updated automatically and vice versa.
For Example.
A user created a new record in Table A. Now the Table B should also be updated with this new information. and vice versa if a user creates a new record in Table B, the Table A should also be updated with this new information.
A user modified a record in Table A. Now the Table B should also be updated with this modified information. and vice versa if a user modifies a new record in Table B, the Table A should also be updated with this modified information.
How can I achieve this. I thought of using triggers but would it not create an inifinite loop resulting is server error!
Is any field among those 5 guaranteed to be unique? You could add a conditional to the trigger to check to see if that field exists before inserting the record in the table.
You might want to rethink the design also. Storing duplicate records in 2 places seems a little scaring. You're going to have to have triggers for updates, inserts, and deletes.
If u just need to update one table in case the other table gets updated, Instead of creating a table (as a part of some other table), create a View which is also like a table but virtual (not real).
but since u've asked for both sides update.
What I believe is that you should go back little back of this problem....and tell us why u need to update both the tables according to the other table,,,
Because you are just keeping duplicate data at two places that is of no need.
So, try to think whether it can be done without creating two tables, or something like create one table and one view for partial columns requirement.
It is not an answer to your problem, but I am trying to solve your problem in an optimized way which is good for everyone's health....
Hope you understood what i tried to tell. :)
I am a bit rusty with mysql and trying to jump in again..So sorry if this is too easy of a question.
I basically created a data model that has a table called "Master" with required fields of a name and an IDcode and a then a "Details" table with a foreign key of IDcode.
Now here's where its getting tricky..I am entering:
INSERT INTO Details (Name, UpdateDate) Values (name, updateDate)
I get an error: saying IDcode on details doesn't have a default value..so I add one then it complains that Field 'Master_IDcode' doesn't have a default value
It all makes sense but I'm wondering if there's any easy way to do what I am trying to do. I want to add data into details and if no IDcode exists, I want to add an entry into the master table. The problem is I have to first add the name to the fund Master..wait for a unique ID to be generated(for IDcode) then figure that out and add it to my query when I enter the master data. As you can imagine the queries are going to probably get quite long since I have many tables.
Is there an easier way? where everytime I add something it searches by name if a foreign key exists and if not it adds it on all the tables that its linked to? Is there a standard way people do this? I can't imagine with all the complex databases out there people have not figured out a more easier way.
Sorry if this question doesn't make sense. I can add more information if needed.
p.s. this maybe a different question but I have heard of Django for python and that it helps creates queries..would it help my situation?
Thanks so much in advance :-)
(decided to expand on the comments above and put it into an answer)
I suggest creating a set of staging tables in your database (one for each data set/file).
Then use LOAD DATA INFILE (or insert the rows in batches) into those staging tables.
Make sure you drop indexes before the load, and re-create what you need after the data is loaded.
You can then make a single pass over the staging table to create the missing master records. For example, let's say that one of your staging table contains a country code that should be used as a masterID. You could add the master record by doing something along the lines of:
insert
into master_table(country_code)
select distinct s.country_code
from staging_table s
left join master_table m on(s.country_code = m.country_code)
where m.country_code is null;
Then you can proceed and insert the rows into the "real" tables, knowing that all detail rows references a valid master record.
If you need to get reference information along with the data (such as translating some code) you can do this with a simple join. Also, if you want to filter rows by some other table this is now also very easy.
insert
into real_table_x(
key
,colA
,colB
,colC
,computed_column_not_present_in_staging_table
,understandableCode
)
select x.key
,x.colA
,x.colB
,x.colC
,(x.colA + x.colB) / x.colC
,c.understandableCode
from staging_table_x x
join code_translation c on(x.strange_code = c.strange_code);
This approach is a very efficient one and it scales very nicely. Variations of the above are commonly used in the ETL part of data warehouses to load massive amounts of data.
One caveat with MySQL is that it doesn't support hash joins, which is a join mechanism very suitable to fully join two tables. MySQL uses nested loops instead, which mean that you need to index the join columns very carefully.
InnoDB tables with their clustering feature on the primary key can help to make this a bit more efficient.
One last point. When you have the staging data inside the database, it is easy to add some analysis of the data and put aside "bad" rows in a separate table. You can then inspect the data using SQL instead of wading through csv files in yuor editor.
I don't think there's one-step way to do this.
What I do is issue a
INSERT IGNORE (..) values (..)
to the master table, wich will either create the row if it doesn't exist, or do nothing, and then issue a
SELECT id FROM master where someUniqueAttribute = ..
The other option would be stored procedures/triggers, but they are still pretty new in MySQL and I doubt wether this would help performance.
I have a table with products. Each product has a title and a price.
The products come in huge XML files, on a daily basis.
I store all of them in MySQL. But sometimes they have a wrong title. But i can't edit it, because they will be lost the next day (cronjob removes all products and inserts again).
What would be the best way to edit them? Save them in a different table and SELECT both tables at once? Whereas the table that contains the edited rows has precedence over the cronjob table.
What would be the best way to handle it, since there are 300.000+ products. Products might be (manually) edited via a CMS system.
Thanks!
Is there some sort of ID that remains constant? (productID) for example?
Can you edit the cronjob?
If both of the above is true; i'd edit the job to only add new records into the table; preventing writing over your updated values.
If there is a unique identifier for each product that remains constant over updates, you could make a table containing the product ID and the corrected title. Correcting a title would involve inserting a row into this table as well as updating the main table.
As the last step of the cron job, you can then update your main table of products from this one.
UPDATE FROM tblProduct p, tblProductCorrections pc
SET p.strTitle = pc.strCorrectedTitle
WHERE p.intId = pc.intProductId