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check the last time the table schema change.

Posted on 2014-01-05
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Last Modified: 2014-01-11
Dear all,

Right now need to check whick table has schema change since the time it create and the last time it change.

should I just use this:

        SELECT *	
    FROM INFORMATION_SCHEMA.TABLES
    WHERE TABLE_SCHEMA='database name' and table_type<> 'view' ;

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and use the UPDATE_TIME field ?
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Question by:marrowyung
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by:Surrano
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Yes but take into account that update_time may be null e.g. for freshly created tables.

select table_name, create_time, update_time 
from information_schema.tables 
where table_schema='dbname' and coalesce(update_time,create_time)>'2014-01-06';

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by:marrowyung
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so null ONLY means for FIRST time created talbe and no schema change after that?

so inserting new record do not affect update_time ?
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by:Surrano
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Yes, NULL means only creation.

No, schema contains only the structure of the table and not the contents. UPDATE_TIME should be the time of the latest DDL command executed on that particular object.
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marrowyung earned 0 total points
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do you tested it on MySQL 5.5? I tested it and it seems that even record updates, this update_time also will change.
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by:marrowyung
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any other way to detect or show out which tables has schema change but not data change ?
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by:Surrano
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Yes, it works for me in mysql 5.5. I gave it a try and found that for some reason update_time is always NULL for me, even after DDL commands, while create_time is updated when I change the table structure.

I suspect it depends on engine: we use InnoDB and update_time is constant NULL. Same for MEMORY, CSV and PERFORMANCE_SCHEMA engines. However, MyISAM engine always has an update time, so it seems. Will be back soon with some more tests.
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by:Surrano
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OK I dug a bit deeper. Update_time is actually the modification time of the data file which means structure *or* data.

Some changes in table structure modify the create_time field (sic!) *but* even some such ddl commands don't change neither create_time nor update_time.

So it's more like create_time you need and even it is not reliable.

The only thing I can come up with as alternative solution is to use "show create table" in two different points in time and you'll be able to tell (most of) the changes that happened between those two timestamps.
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by:marrowyung
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show create table don't show the time, it just provide you the statement to create the table.
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by:Surrano
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yes, it can be used only to compare an "old" version to the "current" version. It makes sense if you do it in an automated and well defined way, e.g. every night you compare the current state to last night's state. But I'm afraid that's the most MySQL (at least 5.5) can offer you. Sad, isn't it.
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by:marrowyung
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one thing is, once show create table, how can we compare 2x very long string ? this is the pint then..
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by:marrowyung
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I just think the other issue, like once we found out the diff. how can we tell what field has been changed? by comparing string, we can only found out the length diff, but not which field it is ?
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by:Surrano
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I'd use the "diff" command. That tells you all the info you need. If using windows, consider having a look at GNU tools for windows (if need a command line tool) or use any file compare tool, e.g. Total Commander.
You may also use a versioning system for keeping track of changes, like SVN or CVS.
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by:marrowyung
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"I'd use the "diff" command."

no! it is my short typing, I don't want to type the whole word..

"If using windows, consider having a look at GNU tools for windows (if need a command line tool) or use any file compare tool, e.g. Total Commander.
You may also use a versioning system for keeping track of changes, like SVN or CVS. "

no,  I need to build an automated method, not like that!!

what if, for any kind of schema cahnge, I tell the developer to include all chance in the delivery notes and I can just cahnge it manually ?

much easlier, right?
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Author Closing Comment

by:marrowyung
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it seems it works in the other way around.
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