Is there any way to create triggers on different databases? my requirement is like:-
database: a1.db consist table: t1
database:a2.db consist table: t2
now i have to use trigger on t1 (whenever any delete and update operation) happens on t1 a value has to be inserted into t2.
waiting for your feedback...
I can only speak for MySQL, but you should be able to do something like:
CREATE TRIGGER ad_t1 AFTER DELETE ON `a1.db`.t1
FOR EACH ROW
INSERT INTO `a2.db`.t2 VALUES (...)
What are the other databases you are using besides mysql? If Oracle is one of them, then you can create dblinks from Oracle to the other databases, and your trigger (running on Oracle) could use those dblinks to update the tables in the other databases.
You can refer to this link for info on creating dblinks in Oracle:
http://download.oracle.com/docs/cd/B12037_01/server.101/b10759/statements_5005.htm
Also, see this link (How to create a DB link between two oracle instances) for another answer on stackoverflow.
Looks like you need the MySQL equivalent of link servers (MSSQL) or dblink (Oracle). There is something called the FEDERATE storage engine:
Check here
Related
I have a database1 in one computer and a database2 (mirrror) in another computer.
Db1 is updated. I should update db2 once a week. To do this task I coulde make a dump from db1 e delete and reload de dump in computer 2. But in fact only one table changes data.
Is there a way to insert into this table (in db2) only the new values from db1 ?
Note: I could do thins using php code. But I am trying to know if is there a way to do that directly in mysql.
To get rows that don't exist use an exception join.
insert into destinationtable
select a.* from mytable a exception join destinationtable b on a.id = b.id
yes..use database replication by SQLYog.. using this technique database values from one server to another or one db to another may be transferred or updated. install SQLYog community edition and follow synchronization tool.
You could use INSERT IGNORE instead of just INSERT. This will only add rows if they don't already exist.
Refer to https://dev.mysql.com/doc/refman/5.5/en/insert.html for more info
I have two MySQL database k_db1 and k_db2 on a single server.
In k_db1, I have k_db1.table1 and k_db1.table2.
In k_db2, I have k_db2.table3 and k_db2.table4.
I want to create a third database k_db3 where I copy/paste tables of others databases.
It will result in k_db3.db1-table1, k_db3.db1-table2, k_db3.db2-table3, k_db3.db2-table4. I want to transfer data, indexes etc... and I don't want to delete k_db1 and k_db2 tables in the process. It must duplicate datas.
Do you know a way to do this just with SQL command?
Thanks in advance for your help.
You can try something like this:
DROP TABLE IF EXISTS k_db3.db1_table_1;
CREATE TABLE k_db3.db1_table_1 AS
SELECT * FROM db1.table_1;
Then you can recreate the indexes on the new table via ALTER TABLE statements.
Also I would avoid using - in table names.
I want to replicate certain table from one database into another database in the same server. This tables contain exactly the same fields.
I was considering to use MySQL Replication to replicate that table but some people said that it will increase IO so i find another way to create 3 Trigger (Insert, update and Delete) that will perform exactly the same thing like what i expect.
My Question is, which way is better? Is it using MySQL replication is better even though it's in the same server or using Trigger to replicate the data is better.
Thanks.
I don't know what is your goal, but I got mine getting use of the VIEW functionality.
I had two different applications with separate databases but in the same Mysql server. Application2 needed to get a few data from Application1. In general, this is a trivial situation that you can handle with USE DB1; or USE DB2; as your needing, but my programming framework does not work very well with multiple DBs.
So, lets see my solution...
Here is my select query to retrieve this data:
SELECT id, name FROM DB1.customers;
So, using DB2 as default schema, I've created a VIEW:
USE DB2;
CREATE VIEW app1_customers AS SELECT id, name FROM DB1.customers;
Now I can retrieve this data in DB2 as a regular table with a regular SELECT statement.
SELECT * FROM DB2.app1_customers;
Hope ts useful. BR
Assuming you have two databases on the same server i.e DB1 and DB2 and the table is called tbl1 and it is sitting in DB1 you can query the table like this:
USE DB1;
SELECT * FROM tbl1;
USE DB2;
SELECT * FROM DB1.tbl1;
This way you wont need to copy the data and worry about extra space and extra code. You can query a table in another database on the same server. Replication and triggers are not your answer here. You could also create a view to encapsulate the SQL statement.
Definitely triggers is the way to go. Having another server (slave) will need to spare several MB for installation, logs, cpu and memory usage.
I'd use triggers to keep both tables equal. If you want to create a table with the same columns definition and data use:
USE db2;
CREATE TABLE t1 AS SELECT * FROM db1.t1;
After that, go ahead and create the triggers for Update, Insert and Delete statemetns.
Also you could ALTER the new table to a different engine like MEMORY or add indexes to see if you can improve something.
Is it possible to use any sort of logic in MySQL without using any procedures? My web hosting does not let me create any procedures so I'm looking for a workaround.
The type of thing I want to do is only add an item to a table if it doesn't already exist. Or add a column to a table if it's not already there. There are some operations that can be done such as CREATE TABLE IF NOT EXISTS and so on, but some operations I require do not have such luxuries :(
I realised late on that my lovely procs won't work and so I tried writing IF/ELSE logic as top-level queries, but for MySQL, IF ELSE blocks only seem to work inside functions/procs and not at the global scope.
Any workarounds greatfully received - I've already asked the hosting to grant me privileges to create procedures but no reply as yet...
I suppose you don't have access to the INFORMATION_SCHEMA either. You can possibly find solutions but it would be better, in my oninion, to:
Change your hosting provider. Seriously. Pay more - if needed - for a MySQL instance that you can configure to your needs. You only have a crippled DBMS if you are not allowed to create procedures and functions.
Posible workarounds for the specific task: You want to add a column if it doesn't exist.
1) Just ALTER TABLE and add the column. If it already exists, you'll get an error. You can catch that error, in your application.
2) (If you have no access to the INFORMATION_SCHEMA) maintain a version of the schema, for your database.
The best solution that I can think of would be to use an additional language with SQL. For example, you can run a query for a specific record, and based on the response that you get, you can conditionally run an INSERT statement.
For inserting a table if it doesn't exist, try using the SHOW TABLES statement and testing whether or not a name exists in the result set.
MySQL supports INSERT IGNORE. and INSERT ... ON DUPLICATE KEY UPDATE.
The following will insert a new row, but only if there is no existing row with id=10. (This assumes that id is defined as a unique or primary key).
INSERT IGNORE INTO my_table (id, col1, col2) values (10, "abc", "def");
The following will insert a new row, but if there is an existing row with id=10 (again, assuming id is unique or primary), the existing row will be updated to hold the new values, instead of inserting a new row.
INSERT INTO my_table (id, col1, col2) values (10, "abc", "def")
ON DUPLICATE KEY UPDATE col1=VALUES(col1), col2=VALUES(col2)
Also, CREATE TABLE supports the IF NOT EXISTS modifier. So you can do something like:
CREATE TABLE IF NOT EXISTS my_table ...
There are many other similar options and modifiers available in MySQL. Check the docs for more.
Originally I created a big script to create or update the database schema, to make it easier to deploy database changes from my local machine to the server.
My script was doing a lot of "if table 'abc' exists and it doesn't have a FK constraint called 'blah'" then create an FK constraint called 'blah' on table 'abc'... and so on.
I now realise it's not actually necessary to check whether a table has a certain column or constraint etc, because I can just maintain a schema-versioning system, and query the DB schema-version when my app starts, or when I navigate to a certain page.
e.g. let's say I want to add a new column to a table. It works like this:
Add a new migration script to the app code, containing the SQL required to add the column to the existing table
Increment the app's schema-version by 1
On app startup, the app queries the DB for the DB's schema-version
If DB schema-version < app schema-version, execute the SQL migration scripts between the two schema-versions, and then update the DB schema-version to be the same as the app
e.g. if the DB's schema-version is 5 and the app version is 8, the app will apply migration scripts 5-6, 6-7 and 7-8 to the DB. These can just be run without having to check anything on the DB side.
The app is therefore solely responsible for updating the DB schema and there's no need for me to ever have to execute schema change scripts on the local or remote DB.
I think it's a better system than the one I was trying to implement for my question.
Is it possible to replicate a single table?
Yes this is possible. Have a look at the slave options of the MySQL manual. This still requires to create a complete binlog of the whole database though.
To sync specific tables again to one or more slaves rather use
pt-table-checksum
and then
pt-table-sync
That should automatically identify the out-of-sync tables and only sync those.
CREATE TABLE new_table_name
SELECT *
FROM original_table_name;
Use "*" if you want to select all columns from the original table, otherwise give specific columns name.
This will replicate table within same database.
I know this is an old question but this is for anyone who comes here looking for an answer:
CREATE TABLE table2 LIKE table1;
This will create a table with the same format and columns but no data. To transfer the data use:
INSERT INTO table2 SELECT * FROM table1;
EDIT:
It is important to note that this is an information transfer only. Meaning if you had indexes on table1 they are not transferred to table2. You will have to manually index table2