Group output of SHOW COLUMNS into comma-delimited

问题:

I am comparing database tables on a development server against a live server, looking for column name changes, new columns, and columns that have been dropped. I'd like to do something like this:

SELECT GROUP_CONCAT(Field) FROM (SHOW COLUMNS ON table_name) GROUP BY Field

What I am after is a comma-delimited list that I can then take to the live server and do:

SHOW COLUMNS FROM table_name WHERE NOT IN ([comma-delimited list from above query])

Any thoughts on how best to do this - either by correcting me in my own approach, or by another means all together? Obviously, the above SQL does not work.

A note: The servers are entirely separate and may not communicate with each other, so no direct comparison is possible.

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EDIT

Thanks for the answers, guys! Applying your answers to the question, this is my final SQL to get the column names:

SELECT CONCAT("'", GROUP_CONCAT(column_name ORDER BY ordinal_position SEPARATOR "', '"), "'") AS columns
FROM information_schema.columns
WHERE table_schema = 'db_name' AND table_name = 'tbl_name'

That gives me a list that looks like this:

'id', 'name', 'field1', 'field2'

Then I can use this query to compare:

SELECT GROUP_CONCAT(column_name ORDER BY ordinal_position)
FROM information_schema.columns
WHERE table_schema = 'db_name' AND table_name = 'tbl_name' AND column_name NOT IN ('id', 'name', 'field1', 'field2')

The results are a list of any columns that exist in the first database and not in the second. Perfect!

回答1:

Take a look at the information_schema.columns table

select group_concat(column_name order by ordinal_position)
from information_schema.columns
where table_schema = 'database_name' and table_name = 'table_name'

edit. Information schema allows you to make queries on metadata. So, you can even compare fields between tables with a left join for example.

edit. Hi Chris. Glad you've solved. As you said your problem was quite different because it concerned with different servers. I add an example of two different databases on the same server.

create database db1;
use db1;
create table table1(
id int not null auto_increment primary key,
name varchar(50),
surname varchar(50),
dob date)
engine = myisam;

create database db2;
create table db2.table2 like db1.table1;
alter table db2.table2 drop column dob;

select i1.column_name from (
select column_name
from information_schema.columns 
where table_schema = 'db1' and table_name = 'table1' ) as i1
left join (
select column_name
from information_schema.columns 
where table_schema = 'db2' and table_name = 'table2' ) as i2
on i1.column_name = i2.column_name
where i2.column_name is null

and the obvious result is dob that is present in table1 and not in table2.

Hope that it helps someone else. Regards guys. :)

回答2:

You should use INFORMATION_SCHEMA.

You can copy the information_schema.columns table from each database into a shared schema and then run SQL queries to compare them.