Pl/sql not null

You can't test for the non-existence of this variable so there are two ways to go about it. Check for the existence of a single element. I don't like this as it means if anything changes your code no longer works. Instead why not just raise an exception when there's no data there:. I realise that the others in the exception is highly naughty but it'll only really catch my table disappearing when it shouldn't and nothing else.

Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Asked 10 years, 4 months ago. Active 7 years, 1 month ago. Viewed 44k times. Sapience Sapience 1, 3 3 gold badges 13 13 silver badges 23 23 bronze badges. Add a comment. Don't worry; Oracle is never going to change this behavior, so you don't have to "take out insurance. Study this Truth Table and make sure you are comfortable with everything you see in it.

You can even verify it to yourself with this LiveSQL script. Notice that if x is null or y is null, then x AND y is always null. The most important thing to remember is that in almost every case if any part of your expression evaluates to NULL , the entire expression will evaluate to NULL.

In addition, pay close attention to how you construct conditional statements and expressions, when an expression might evaluate to NULL. But what if you want to treat two NULL s as being equal when you compare two values?

Marcus in the comments below suggests creating an isEqual function that handles this for you. Here's the implementation of Marcus's isequal function for dates:. It is also a statement , albeit a ''no-op" no operation -it only passes control to the next statement. Here are two examples. Null values can be a real pain. They can cause unexpected failures and exceptions in your algorithms. They can mess up queries, either returning rows you didn't want or excluding rows when you want them. So, the first thing to do is to decide very carefully where and when you want to allow nulls.

If a column's value should never be null, then define it that way. If you are writing a subprogram procedure or function and a parameter's value should never be null, you cannot add NOT NULL to the parameter definition. Instead, you will need to do one of the following:. Use a datatype for the parameter that cannot be null.

See the examples below. Add code to your subprogram to check or assert that the actual argument value is not null. Then, you declare your own subtype and make that new datatype not-nullable. Let's take a look:. Note that the exceptions raised above occur before the procedure is even executed, so the exception handler of the procedure cannot trap the exception you do not see "Error!

That may be just what you want. But if you cannot use a NOT NULL datatype for your parameter or you want to be able to trap the exception inside the subprogram, then you should write your own assertion code that runs right at the top of the subprogram.

This affects how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator. Here, operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators will be evaluated first.

Previous Page. Next Page. Previous Page Print Page. Save Close. Checks if the values of two operands are equal or not, if yes then condition becomes true.