Trigger updating column oracle
Imagine you have a huge table – 1 million rows – and you need to update a column. If you have triggers on the table, not even Nostradamus knows how many records across the database were really updated. Triggers are also a convenient hiding place for bugs. Tom Kyte points out another reason to be wary of triggers. And it’s not just utl_mail; the same thing would happen with utl_file, utl_http, and many other utl_ functions.It’s a huge task, but your table is properly indexed so you’re not too worried. Two hours later you’re sitting there scratching your head. Imagine you write a simple statement to update 10 records and run it. When your code errors, it is natural to go over the code you have just written looking for fractures in the logic; no one ever remembers to look in the triggers that may be firing in silence. In fact, in researching this article, I learned that I was wrong when I wrote that simple triggers to populate primary key columns from sequences are pretty uncontroversial. They recommend that you build APIs to interact with your tables, and populate your primary key columns that way. Imagine you maintain a database for a business that sends a £5 discount code to every customer who makes a purchase. The customers are probably blowing your cash right now. And it is a popular practice to write audit records using autonomous transactions fired from within triggers. If your main process is rolled back, you’ll be left with your audit records. At this point you’re probably asking the sensible question: if triggers are evil, why do they exist?with parenthesis “()” - this is because what we want in this case is the return value of the function, which is the SQL expression construct that will be rendered into the INSERT or UPDATE statement. And it’s pretty unanimous – from luminaries like Tom “Triggers are evil” Kyte to people like this dude (“Triggers are powerful – and much despised”). To answer your question, let me start by quoting myself again: Simple triggers to populate primary key columns from sequences are pretty uncontroversial; however, there is no upper limit to their potential complexity. This statement can be used with any interactive tool, such as SQL*Plus or Enterprise Manager.When using an interactive tool, a single slash (/) on the last line is necessary to activate the 0) DECLARE sal_diff number; BEGIN sal_diff := :- :old.sal; dbms_output.put('Old salary: '
For each row inserted into SALES, the trigger makes a call to utl_to automatically send an email containing the discount code to the customer. And yes, I still use them to populate primary key columns that depend on sequences. And, despite highlighting the danger of using them for auditing, we do still maintain some legacy code that does that. Yes, I confess that the main database I work with still has a number of triggers in it, and I know that that makes me sound hypocritical. David Njoku is a software developer at Northgate Public Services.
the column value after it has been inserted to the table.