Is it possible to alter the schema of a mysql table by simply providing the new schema and having the database figure out how to migrate? For example, let's say I have a table with two columns: id, name. I want to modify this table by adding a new column: title. I know that I can issue the command ALTER TABLE tbl ADD COLUMN title. Is there a way I can just provide the complete schema and have mysql figure out that it needs to add a title column?
I hope that makes sense what I am asking.
MySQL can't do this by itself, but I found a blog that says MySQL Workbench can do it.
No - It cannot do that just giving your database a new schema. It would have to go about and second guess what to do with the data. (Also what happens to triggers, stored procedures ...)
You have a couple of choices
Modify each table and decide what needs to be done
Export the data, create a new database and then figure out how to import it into the new regime.
Related
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 am using MySQL to capture snapshots of my data everyday, so I need to create multiple tables with the same columns.
my_foobar_table_20170125
my_foobar_table_20170126
my_foobar_table_20170127
What's the easiest way to create the tables? Would it be with a table schema file? Or, with a create table query?
I am leaning toward using a table schema file if that is possible. As it seems cleaner than a sql query to create the table.
I have googled around, and surprisingly there is no clear answer on this. In fact, it's not even obvious what exactly is a "table schema file", or how to generate this from mysql workbench, or use the schema file to create the table.
Definitely create a table .sql file and load it into MySQL then log in. Manually making it each time is a ton of work and this allows you to also customize each table if needed, and to use drop database and to refresh easily as well.
CREATE DATABASE databasename;
USE database;
CREATE TABLE tableofthings (
ID INT NOT NULL AUTO_INCREMENT,
otherdatastring VARCHAR(50)...
PRIMARY KEY (ID)
);
...then put other tables below...
While Altering a table in mysql to Add a new Column I am getting Fatal Error Occurred.. I ve seen the relevant answers for this question where I found an Answer like :--
Make a new table with the same structure.
Add the column to the new table.
Insert the data from the old table into the new table.
Rename the old table to old.bak
Rename the new table to the old table.
If all went well, delete the old.bak.
But my original table contains some triggers , indexes, etc.
My question is
"Can I write my Alter Script in any diff. way to overcome this fatal Error" ?
My concern is related to MYSQL, but any other RDBMS related answers also fine...
This is MySQL specific: You can use a combination of [SHOW CREATE TABLE tabname][1] and [SHOW TRIGGERS WHERE Table = 'tabname'][2] to regenerate the table and triggers. You probably don't want the triggers firing when you are copying the rows. Also, if the table is of a significant size or you have a high enough rate of change, you probably want to prevent writes to it during the copy.
Sequence of steps:
Prevent writes to table (optional)
Create new table with SHOW CREATE TABLE output.
Apply schema changes.
Copy data from old table to new table.
Apply triggers from SHOW TRIGGERS output.
Swap old and new tables.
Hope this helps.
Is there a way to do this?
In case the DBMS command history got cleaned or, in my case, when many ALTER TABLE were used in the course of time.
I'm using MySQL.
Yes, it is as simple as
SHOW CREATE TABLE yourtable;
This will include all the subsequent ALTER TABLE statements. You cannot retrieve the table's original state.
Here is the relevant documentation
MS SQL Server has a TABLE data type which can be used in stored procedures,
Does anybody know if MySQL has an equivalent data type?
I've had a look over the docs but can't seem to find anything, so I presume it doesn't exist, but perhaps somebody has created a workaround
Neil,
MySQL has no such data type and I believe it is good that it doesn't. To achieve similar results, use CREATE TEMPORARY TABLE construction. Name clashes are avoided by having per connection temporary tables:
A TEMPORARY table is visible only to the current connection, and is dropped automatically when the connection is closed. This means that two different connections can use the same temporary table name without conflicting with each other or with an existing non-TEMPORARY table of the same name. (The existing table is hidden until the temporary table is dropped.)
Hope it helps.