I'm working with phpmyadmin and I have to merge two db with same structure but different data.
The db have relation between tables (foreign key).
The data in two db may have same id, and so their foreign key.
I would like to know if it's possible merge the two db keeping all data, so, if a row already "exist", insert it with new id and update its foreign key.
thanks a lot
No easy way unfortunately. If you have TableA as a foreign key to TableB, you will need to
1) Insert data from source tableA to target tableA
2) create a (temp) table to store the mapping between source tableA ids and target tableA ids
3) Use this mapping table when inserting data from tableB to convert the tableA ids to the new ones in the target db
... and so on. It can get quite hairy if you have a deep hierarchy of tables, but hopefully you get the idea. Take backups before you start.
Another idea that you might want to consider is using a cursor:
Assume table A is the one that you want to keep and table B is the one you want to remove.
Declare a cursor for table B and select all the records.
Loop each record selected from the cursor and check.
Case 1: If the ID is exists on table A, insert the record to table A with same details.
Case 2: If the ID is exists on table B, insert the record and modify the ID and foreign key.
Once all the records have been checked, drop table B.
Sorry, I just can give an idea at the moment.
Related
Here's the scenario, there are 3 tables:
table1
table2
table1_to_table2 - junction table linking table1 and table2
When a row is deleted in table1, all references of that row must also be deleted in the junction table. It is possible that after some time there are no more rows in the junction table referencing any rows in table2.
You can define in the junction table , ON DELETE CASCADE, so that when there are records deleted in table1, rows referencing it in junction table would also get deleted. And you can be implement manually in your application to cleanup table2 every delete. But, is there a way to define the schema in mysql, so that automatically it ensures that when this happens, the rows in table2 will be cleaned up?
There is no default way of doing this. You are going to have to perform a check On Delete of a row in the Table1_to_table2 table.
I don't see a way to do this via schema definition.
You can protect that rule by coding it inside an Stored Procedure bound to DELETE on table1.
I have a scenario that requires a value in a row of a table to be updated automatically whenever a row has been added or deleted in another table. I'm not sure how to do it.BTW I'm using phpmyadmin in order to manage my database. Thanks in advance.
pages Table
------------
page_no
no_of_choices
choices Table
-------------
page_no
choice_no
When I add a choice with choice number 1 and page_no, then the table page which has the row, page_no=1 should be updated with no_of_choices=no_of_choices+1
You can use triggers.
For example:
CREATE TRIGGER `test1`
AFTER INSERT ON `tbl1`
FOR EACH ROW SET NEW.upd_fld = new_value
Similarly could be done for delete.
You can also create triggers from phpMyAdmin
TABLE A: page_no, no_of_choices
TABLE B: page_no, choice_no...
With a relational database you very rarely want to have duplicate data. If something breaks at some point, you won't know which to trust - the rows in Table B, or the no_of_choices in Table A. A better solution is to do one of the following (depending on which table you are querying):
SELECT COUNT(no_of_choices) FROM B WHERE page_no = 1
or
SELECT A.*, COUNT(choice_no) AS choice_no FROM A LEFT JOIN B USING(page_no)
You get the same result, but now you have one record to go off of, so you won't have inconsistent data.
Two tables share a unique identifier 'id'. Both tables are meant to be joined by using 'id'.
Defining 'id' as an auto incrementing primary key in both tables may risk update inconsistencies.
Is there some general pattern to avoid such a situation or do I have to deal with updating table1 first and table2 by utilizing the last inserted id after (therefore not declaring id as auto inc in table2)?
First, if you use InnoDB table engine in MySQL you could use both transactions and foreign keys for data consistency.
Second, after the insert in the first table, you could get the last insert id (depending on the way you access the db) and use it as foreign key.
Eg
Table 1: Users: user_id, username
Table 2: User_Profiles: user_id, name, phone
In User_Profiles you don't need to define user_id as auto increment, but first insert a record in Users table and use the user_id for the User_Profiles record. If you do this in transaction, the Users record won't be seen outside of the transaction connection until it's completed, this way you guarantee that even if something bad happens after you insert the user, but before you have inserted the profile - there won't be messed up data.
You could also define that the user_id column in User_Profiles table is foreign key of Users table thus if someone deletes a record from the Users table, the database would automatically delete the one in User_Profiles. There are many other options - read more about that.
There is no problem with same column name 'id' in any number of tables.
Several persistence layer frameworks do it same way.
Just use aliases in your SQL to distinct your tables accordingly.
do I have to deal with updating table1 first and table2 by utilizing the last inserted id after (therefore not declaring id as auto inc in table2)?
Yes. And make id a foreign key so it can only exist in table2 if it already exists in table1.
Yes you do, and remember to wrap the operation in a transaction.
I am having my application deployed on two separate regions say US-WEST and EU, both application has its own DB. And now I want to move the EU region DB to US-WEST.
This will lead to primary key collision since both the db has the tables with same primary auto increment id, can anybody give me suggestion to solve this.
Scenario:
User Table from DB1(say from US-WEST) has the following entries
ID Name
1 Rob
2 San
3 Tulip
User Table from DB2(say from EU) has the following entries
ID Name
1 John
2 Michael
3 Natasha
For every one of the two original databases (say db0 and db1):
Back up the db.
Lock database for use by this script only.
For all the tables in the database that have foreign keys defined without ON UPDATE CASCADE, change all these foreign keys constraints with this option.
For every table with an auto_increment (or a simple integer) Primary Key, run this (the cascading updates will make the rest):
.
UPDATE TableX
SET Pk = 2 * Pk - 0 --- for db0
ORDER BY Pk DESC
UPDATE TableX
SET Pk = 2 * Pk - 1 --- for db1
ORDER BY Pk DESC
Export the tables from each database.
Now merge the two databases by simply merging the corresponding tables. All data from db0 will have even ids and all from db1 will have odd ids. No collisions.
For tables without auto-incrementing Primary Keys or for tables which may have common rows, the merging should be different, off course.
Unlock.
You can read about auto_increment_increment and related system variables that you can change so from this point, the two databases produce different auto incremented ids (one odd ids, the other even ones).
Turn off auto-increment in your destination DB. Then first import data from DB1 and the from DB2. In your importing from DB2 add a constant value that is higher than your hightest id in the first DB. Like this:
insert into destination_table
select id + 10000, othercolumns from source_table
After importing the data you can turn on auto-increment again.
EDIT :
If your id column references to other tables then this method will break the relation to these tables.
I think you have to extend your destination DB with a column for example regionID and edit the primary key settings for this table. Use a Primary key with the two columns ID and regionID. Then import the data from the two tables like this:
Insert into destination_table values(regionID, ID, Name)
select 1,ID, Name from DB1
Insert into destination_table values(regionID, ID, Name)
select 2,ID, Name from DB2
Now, the tricky part. You have to do this for all tables, where you use the ID as a relation. After transferring all data you only have to edit your SQL statements to use regionID and ID combined as key.
Remove primery key and Turn off auto-increment from id field your destination DB table.
Then first import data from from both DB.
Delete id column from destination table.
Create again id column make that column auto increament primary key.
Let's say I have a table, category, which has 3 columns, id, parent_id and name.
I have several tables like this, and I want to consolidate them into one. At present, their IDs will clash (not unique across DBs) so I need to re-ID them. If I make id an auto_increment I can copy all the other columns over just fine, but then parent_id won't link up properly anymore. Is there some magical way I can get the parent_id to point to the correct new ID?
Looking for something like
INSERT INTO newtable (parent_id, name) SELECT ???, name FROM oldtable
How about
Generate a new table with a column containing the name of the old table and old id (oldid, oldtablename) along with a new ID
Add a new column 'newparentid'
Update each row's newparentid to be (SELECT newid FROM newtable nt WHERE oldtablename = row.oldtablename and nt.oldid = row.parent_id)
I imagine you could add an old_id column so that you'll still have the original id and you can run successive updates to the table to modify all the parent_ids to point to the new auto_inc ids. You would obviously have to kill any foreign keys requirements on the table first and reinstitute them after all the changes were made – Patrick