I have a set of databases and each of them contains a table named 'data'. I would like to add a new column to the table 'data' in all databases. Is it possible to do this with a sql statement? And would it work on MySQL 3.x server?
As far as I know you must do an "Alter Table" on every table of every database.
Related
I have a set of database schemas, with each one having the same set of tables.
I want to alter a table by adding a column in each one of the schemas with a single command, instead of doing it for every schema separateley.
Is that possible?
This isn't quite identical to Querying multiple databases at once but it's similar. As in the linked question, you could write a procedure:
Get the schema names from information_schema.tables
Create your query template
Loop over the schema names and for each schema sub the schema name in the query template
I want to make a new table like as an existing table in MySQL database with some "column name" changes. So, is there any way to see the SQL dump of the existing table without importing?
You can use SHOW CREATE TABLE:
SHOW CREATE TABLE oldtable
I have two databases. Now I'm trying to import all table schema only from first database to second database. I already exported all table structure from first database using phpmyadmin. But I can't import the table structures in the second database. phpmyadmin says
#1050 - Table 'XXXXXX' already exists
How can I import only the table structure correctly?
Note: Both databases had same table and all table had same structure. I have changed some table structures in the first database that I can't remember right now. Now I need to merge both table structure only. Also both database contains different data set and I can't afford any data loss from both databases.
Before executing any command I would recommend taking full database backup, otherwise you may lost a few days of sleep.
Using ALTER command
Use ALTER command to modify table structure. Here's sql that adds age not nullable age field to users table.
ALTER TABLE users ADD age int(11) not null
Re-creating table
I wouldn't recommend this method because you'll have data loss. Drop old table then create with new schema.
DROP TABLE mytable;
CREATE TABLE mytable (
...
);
Or if you want to keep data you can:
Duplicate or rename table to different name.
Create a new table with new schema.
Copy data from old table: INSERT INTO newtable SELECT * FROM oldtable
Renaming tables might cause relationship issues. I would recommend using ALTER command as much as possible. You can also take a look at scheme migration(aka: code first migration, database migration).
The main Issue is merging the tables. To identify the differences between the two tables I use a small software called SQL Power Architect.
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'm attempting to merge data from one MySQL database into another. The problem is, some of the tables in Source_DB have fields that the matching table in Target_DB does not have.
Is there a way to automatically ALTER the table in Target_DB to add these missing fields as they are found?
Or should I go about it another way, like doing a first pass where I compare each table to first add any missing fields?
You could query the INFORMATION_SCHEMA.COLUMNS on each DB and figure out what's missing with a NOT IN query and then using the data in the INFORMATION_SCHEMA.COLUMNS dynamically generate the DDL.
Or you could use a tool like MySQL Compare to do it.