I am new using mySQL, so probably my question will be very banal, but I didn't find any solution on internet.
I have two tables, TABLE 1 and TABLE 2, each one with a single primary key tab1PK (INT) and tab2PK (VARCHAR).
Since TABLE 1 and TABLE 2 have a M:N relationship, I have a third table, TABLE 3, whose PK are two: tab1PK and tab2PK.
I generated random data for TABLE 1 and TABLE 1. Is there a way to generate rapidly data for the TABLE 3? Is there a way to easily combine tab1PK and tab2PK?
This will give you a cartesian join of all table1 & table2 primary keys.
insert into table3 (tab1PK, tab2PK)
select table1.tab1PK, table2.tab2PK
from table1, table2
Related
I am using join in my quires and i want to know if the relations between database tables leads to increase performance of the queries.
Thank You.
For boosting performance, you should use indexes, use appropriate datatypes as well (storing number as string takes more space and comparing may be less efficient).
Relations between tables, i.e. foreign key are constraints, so you cannot enter new value to referenced table without referencing records in other table - it is a way to keep data integrity, eg.
Table1
id table2_id
1 1
2 1
3 3
Table2
id some_column
1 123
2 123
3 null
Here, Table1.table2_id references Table2.id. Now you won't be able to insert such row to Table1: 4, 4, because there's no id = 4 in Table2.
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.
I have two tables with identical structures. Let's call them table A and B.
Table A consists of records with ID as primary key from 1-10 and B has the table with IDs 11-20.
Given I have imported table A into mysql table, how can I, in a way, concatenate table B to A?
Any thoughts will be much appreciated :D
You use insert:
insert into tablea
select *
from tableb;
It is better to list the columns for the insert and select, but you can do it with this syntax if the tables really do have identical formats.
I have three table TableA,TableB and TableC
TableA
idA ------------ PK
col1A
TableB
idB ----------- PK
col1B
TableC
idC ---------- PK
col1C
I am indexing all the data in solr in single core there may be a chance of overriding TableC data with TableB or TableA and Vice versa. Because the primary key are auto generated and there is a possibility of having same value in different tables. How do I solve this problem.
I have two solutions.
1) I was thinking of appending a suffix pk_tablename to make the unique id in solr.
2) create separate core for each table.
which do you suggest is the best ?
In my business domain the table can have millions of records.
please advise.
Solution 1 should be fine. You can store data from different tables in a single core if you want to search them all with a single query. Your primary key is fine. Along with that you can also store the table name in another field, so your docs will look like:
{
unique_id: 1234_A,
id: 1234,
table: A,
data: <text field>
}
Storing the table name will help you perform searches restricted to some table(s) only.
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.