Oracle trigger if updating column. Before, after, each row and table level triggers [Oracle].



Oracle trigger if updating column

Oracle trigger if updating column

So most implementations I have seen use other approach. You can test inserted and deleted pseudo-tables available in trigger for presence of data. I never realized this before, but you shouldn't assume that the trigger is fired for DELETE because there are no rows in inserted, because it may be fired for UPDATE where no rows match the criteria - and both inserted and deleted tables will be empty. How to know which columns have been changed? SQL Server provides two methods of finding out which columns have been updated during particular operation: So, you can implement a trigger that will react to particular column update more or less like this: You can audit change of this column, you can trigger some actions that have to happen when this column is updated, eventually you can calculate some other values possibly in other tables based on new value of the column.

You can also rollback the transaction if the new value of column doesn't meet business or integrity requirements. The drawback of this method is that you have to check condition for every column and you have to deal with column names and for a hundred columns in a table it is really not a feasible option. It is worth to mention here that 'changed' doesn't mean that they values were changed, it means that columns where on the left side of assignment operator in update statement.

Its length depends on the number of columns that are defined in the table. Each byte will contain mask for eight consecutive columns, and the last byte will keep mask for the remaining columns.

For up to 8 columns there is going to be 1 byte, for 12 columns 2 bytes, for 17 columns - 3 bytes. The value is as I said divided into bytes, and each byte contains bit mask for eight consecutive columns.

The catch is that bytes are ordered left to right: You end up with something like this: What can you do with this bitmap? If you want to check if particular column was updated, first you have to select the byte relevant for this column and then check if the flag for the column is set to 1 or 0.

There is another formula, and this is the last one in this post: So the formula looks like this: We know all the formulas required to get updated column information from the bitmap, how to use this in a trigger? Many developers use in this case a loop that calculates the byte, mask and retrieves name of the updated column. I am not going to do this. Some time ago I wrote about numbers table , and you can find there links to clever and very useful implementations of this technique.

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SQLite: How to update tables using triggers



Oracle trigger if updating column

So most implementations I have seen use other approach. You can test inserted and deleted pseudo-tables available in trigger for presence of data.

I never realized this before, but you shouldn't assume that the trigger is fired for DELETE because there are no rows in inserted, because it may be fired for UPDATE where no rows match the criteria - and both inserted and deleted tables will be empty.

How to know which columns have been changed? SQL Server provides two methods of finding out which columns have been updated during particular operation: So, you can implement a trigger that will react to particular column update more or less like this: You can audit change of this column, you can trigger some actions that have to happen when this column is updated, eventually you can calculate some other values possibly in other tables based on new value of the column.

You can also rollback the transaction if the new value of column doesn't meet business or integrity requirements. The drawback of this method is that you have to check condition for every column and you have to deal with column names and for a hundred columns in a table it is really not a feasible option.

It is worth to mention here that 'changed' doesn't mean that they values were changed, it means that columns where on the left side of assignment operator in update statement.

Its length depends on the number of columns that are defined in the table. Each byte will contain mask for eight consecutive columns, and the last byte will keep mask for the remaining columns.

For up to 8 columns there is going to be 1 byte, for 12 columns 2 bytes, for 17 columns - 3 bytes. The value is as I said divided into bytes, and each byte contains bit mask for eight consecutive columns. The catch is that bytes are ordered left to right: You end up with something like this: What can you do with this bitmap? If you want to check if particular column was updated, first you have to select the byte relevant for this column and then check if the flag for the column is set to 1 or 0.

There is another formula, and this is the last one in this post: So the formula looks like this: We know all the formulas required to get updated column information from the bitmap, how to use this in a trigger?

Many developers use in this case a loop that calculates the byte, mask and retrieves name of the updated column. I am not going to do this. Some time ago I wrote about numbers table , and you can find there links to clever and very useful implementations of this technique.

Oracle trigger if updating column

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4 Comments

  1. I have a sequence of insert, after insert trigger update, and query operations and my problem is that the data received from the query does not reflect the updates performed by the trigger even though the data in the database is indeed updated. However, Transact-SQL includes an extension to the language that allows you to select TOP values with a view; to support that, it also supports sorting. In your table element in your schema, do this:

  2. If you have a table in Oracle database whose primary key column is filled by a unique Oracle sequence, Telerik Data Access can automatically detect that the table has a server side generated primary key mechanism.

  3. Full-text indexes can't be defined on views. The catch is that bytes are ordered left to right: You've found that BookPeer::

  4. However, Transact-SQL includes an extension to the language that allows you to select TOP values with a view; to support that, it also supports sorting. The cursor is because an update trigger fires on an update statement which may impact more than one row - it does not fire once per record like an Oracle trigger can.

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