Under the structure tab, when EXPORTing a database using phpmyadmin there is a check box labeled:
Add DROP TABLE / VIEW / PROCEDURE / FUNCTION
What does this do?
When creating a table, view, procedure, or function, it will add a DROP statement before it. The result of this is that even if the item exists, it will still be created.
For example: If you have a table called users and you run the export script without the DROP checkbox, it will attempt to create the users table again but will fail since it already exists. If you check it, it will drop the table before it is created (if it exists) to ensure the creation will always be successful.
Of course this can be dangerous if you have data in the table that you don't want to lose.
For example: If you have a table called users and you run the export script without the DROP checkbox, it will attempt to create the users table again but will fail since it already exists. If you check it, it will drop the table before it is created (if it exists) to ensure the creation will always be successful.
I was confused as to what this statement meant exactly, so I did additional research on the topic and wanted to leave an elaborated explanation here for future reference.
The create and drop actions in the above quote are simply instructions for when you import the file you have already exported. I was initially under the impression that these actions were happening as I was exporting. This is not the case. It's simply instructions for when you import your exported file.
Related
I have a table set up to track when people place an order (Order_Tbl). I duplicated the table that I call my order_change_log and added a date/time field (default value set to now). I have a one to many relationship between the orderID and order_change_logID. The idea is that before update, I want the existing data to be inserted into the change log table. I went into the before update field and made the following statement:
CurrentDB.Execute “INSERT into Order_Change_Log SELECT * FROM Order_Tbl WHERE ChangeLog_ID =“”” & Me.ID & “”””
I keep getting “Invalid Outside Procedure” and I’m getting frustrated… Not sure what I’m doing wrong.
What you want to do is called a trigger. In access a table's triggers can be accessed and created from the table's design mode via [Create Data Macros] on the ribbon. You are pretty much forced to use the macro language to create the trigger.
As an aside it looks like you are setting the default date in Order_Change_Log. Leave that default blank as it is not needed here and in many other cases leads to bugs.
In this case we will be using the after-update macro. The Before-Update values are available using [Old]
For an older example of a trigger happening after Delete see MS Access trigger?
Example Table and Relationships:
After Update Trigger Macro:
Use the ribbon to save the macro and you are done. change some values in the Order_Tbl then refresh or open the Order_Change_Log table to see the results
The subject line actually says it all.
I have a schema, now when I create a forward script it generates the tables and I added the option to do a DROP TABLE IF EXISTS in front of every create table SQL. The creation part is fine. But if you run the script twice you notice that the drop sequence is the wrong order.
I think the concept of aligning the drop sequence with the create sequence is just conceptually arguable. I think you might be able to create schemas where you won't be able to create the tables in the same sequence as you would drop them.
Anyhow, I can't find any option to change the order or do anything. Has anyone an idea how I can change the drop sequence manually ?
I am sorry to be not able to share any SQL, however I think the problem is really generic. And you want solve it by writing different SQL. So it should be possible to answer based on discussion, not on code.
That's Workbench version 6.3.6. So almost latest. (Currently 6.3.7)
You must drop table in reverse order of creating them.
When creating:
Create table a...;
Create table b...;
Create table c...;
When dropping:
Drop table c;
Drop table b;
Drop table a;
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.
I want to get the new table definition(create table statement) and save it to a txt file when the ddl alter table trigger fires.
I have tried xp_helptext, this only works for view or stored proc. I hope there's something like this for altering table to get new create statement.
I have also tried use xp_cmdshell to launch a .net. And hard code the script according to the info from INFORMATION_SCHEMA. However, it is locked because the trigger is not closed during the .net is running.
You can't do this. SQL Server does not generate a new CREATE TABLE statement when you run an ALTER TABLE. You will see that EVENTDATA() in your DDL trigger only contains the ALTER command, not the entire table definition. You will also notice that neither INFORMATION_SCHEMA nor the catalog views like sys.tables ever store a copy of the CREATE TABLE generation, even when the original command was CREATE TABLE, so there is nothing to get from that route.
You can see what Management Studio does to generate the create table script by running a server-side trace, then right-clicking a table and choosing Script As > Create To > New Query Editor Window. I can assure you this is not some simple SELECT create_table FROM sys.something but rather a set of metadata queries against a slew of DMVs. You don't even see the CREATE TABLE being assembled because it is done in the code, not from the database or in the query.
More accessible: SMO has methods for scripting objects such as tables. But I don't think you should try to do this from within the trigger - bad idea to make the ALTER TABLE transaction wait for your ability to invoke some external process, write to a file system, etc. Here is what I propose: when a table has its definition changed, in the DDL trigger add a row to a queue table. On the OS have a PowerShell script or C# command line executable that uses SMO methods to generate the script given a table name. Schedule that script to run every minute or every 5 minutes, and check the queue table for any new alters that have happened but that you haven't captured. The program writes the file based on the CREATE TABLE script that SMO generated, then updates the queue table (or removes the row) so that it is only processed once.
Is it true I can't edit a MySQL trigger, I have to drop it and create a new one?
Also, being a relative newcomer to triggers, it feels like they seem liable to causing 'erroneous' data. For example I might want a trigger to be fired (inserting data into another table) after one particular type of update query, but not others.
Any tips here gratefully received!
Edit: Yes, it is true that versions 5.n and 6.n of MySQL 5 & 6 implement CREATE TRIGGER and DROP TRIGGER and nothing else. According to this hunk of Postgres documentation, there is not even CREATE TRIGGER in SQL 92, so consider yourself lucky to have TRIGGER at all :-)
The Visual Studio MySQL plugin documentation has:
To modify an existing trigger, double click on a node of the trigger you wish to modify, or right click on this node and choose the Alter Trigger command from a context menu. Either of the commands opens the SQL Editor.
... which seems to do what you want. My guess is this is GUI sugar and behind the scenes you get a DROP CREATE.
As far as a trigger for some UPDATEs and not others, SQL has exactly one UPDATE per table. Put an IF clause at the start of your UPDATE trigger so that your logic - whatever you are doing in some of your UPDATEs - is only executed when you think it is appropriate.
MySQL has REPLACE TRIGGER, right?
As a sidenote.. Is it an issue? If you're worried queries are executed in between DROP and CREATE, you could always lock the table beforehand.
If you're using MySql Workbench it will allow you to alter the trigger. Just right click on your table name and click Alter table option from there you can pick Trigger option and alter it. Although, you cannot perform it from query mode.
Table Name --> Right Click --> Alter Table --> Triggers.