Merge databases with duplicate object id's - mysql

Question

I have two databases that I would like to merge, the problem is it has around 20 tables that are relevant and have unique object id's that are linked into each other. in example Table names:
name
object_id
FirstName
500
and then it has tables like Items:
item_name
object_id
item_id
itemNr1
500
400
the third table would be Items_specialty:
specialty
item_id
specialty_id
power1
400
600
as you see they all are tied together name's object id is attached to item and item id is attached to specialty_id.
however in two databases object_id, item_id and specialty_id are duplicating, and when I'm talking about nearly 100,000 rows it get's complicated and concern of loosing object id's is high as if that would happen different names would have different items etc. so what would be the best way to merge it while maintaining all object id's to specific name and follow the trail through the tables updating them all together?
Ideal solution would be check whether object_id+1 is not used and if not apply it and then do the same in all further tables, doing the same for item_id and specialty_id, where at the end same name would hold same item and specialty with it.
Really appreciate any tips or possible solutions to explore, was searching the internet far and wide but without having to pay thousands for a tools can't seem to find a solution that would fit my issue, as usually people only got to merge couple tables instead of many like mine.
Thank you in advance.

Answer 1

(The queries used in this method are for sql server. You need similar queries in mysql to run correctly.)
Database merge requires a thorough understanding of the data and the design of the database.
For example, the following solution can be used to merge these two databases:
1- With the following command, you can remove all the restrictions of the second database in sql server:
use db2;
DECLARE #sql NVARCHAR(MAX);
SET #sql = N'';
SELECT #sql = #sql + N'
ALTER TABLE ' + QUOTENAME(s.name) + N'.'
+ QUOTENAME(t.name) + N' DROP CONSTRAINT '
+ QUOTENAME(c.name) + ';'
FROM sys.objects AS c
INNER JOIN sys.tables AS t
ON c.parent_object_id = t.[object_id]
INNER JOIN sys.schemas AS s
ON t.[schema_id] = s.[schema_id]
WHERE c.[type] IN ('D','C','F','PK','UQ')
ORDER BY c.[type];
--PRINT #sql;
EXEC sys.sp_executesql #sql;
2- In the first step, we start merge the tables that do not have an external key with the first database, and at the same time enter the data into the tables of the first database, with the newly generated values ​​(I assume that your tables have identity), We update the related tables in the second database. For example, look at the following command:
declare #I int = 0
declare #count_t1 int = (select count(*) from table1)
DECLARE #LAST_object_id INT = 0;
DECLARE #OLD_object_id INT = 0;
WHILE #I < #count_t1
BEGIN
SET #LAST_object_id = 0;
SET #OLD_object_id = 0;
INSERT INTO db1.dbo.table1
(
name
)
SELECT
name
FROM db2.dbo.table1
ORDER BY db2.dbo.table1.object_id
OFFSET #I ROWS FETCH FIRST 1 ROWS ONLY
SET #LAST_object_id = (SELECT TOP(1) object_id FROM db1.dbo.table1 ORDER BY db1.dbo.table1.object_id DESC)
SET #OLD_object_id = (SELECT object_id FROM db2.dbo.table1 ORDER BY db2.dbo.table1.object_id OFFSET #I ROWS FETCH FIRST 1 ROWS ONLY)
UPDATE db2.dbo.table2
SET object_id = #LAST_object_id
WHERE object_id = #OLD_object_id
SET #I = #I + 1
END
3- In this step, we will merge the tables with the first database that have foreign keys, but we know that their foreign keys have been updated in step 2.
4- Repeat step 3 for the depth of the database to reach tables whose primary key is not an foreign key for other tables. Then we merge those tables with the first database.
Remember: If the values ​​of the first database tables are less than the values ​​of the second database tables, the probability of error in that method increases. So you need to control how identity grows in sql server with the following command:
DECLARE #MAX_0_object_id INT;
DECLARE #MAX_1_object_id INT;
SET #MAX_0_object_id = IDENT_CURRENT('db1.dbo.table1')
SET #MAX_1_object_id = IDENT_CURRENT('db2.dbo.table1')
IF #MAX_1_object_id > #MAX_0_object_id
BEGIN
DBCC CHECKIDENT ('db1.dbo.table1', RESEED, #MAX_1_object_id)
END