Luckily Oracle provides us with a couple of functions to do the heavy lifting when it comes to checking for NULLs. If you want to see all the employees with no commission filled in you can issue a statement like this:. Notice NULL is not the same as 0 zero. In the one before it, it was possible to convert 2 to a varchar2 value. If expr1 contains a NULL value, then return expr3.
If the value of expr1 contains a non-NULL value, then return expr2. If they are not equal expr1 is returned. Expressions must be of the same data type, There is no implicit conversion performed. The coalesce function returns the first non-NULL value of the expressions in the list. The list must consist of at least 2 values. When a column in a table is defined there is the possibility to have a default value for this column whenever it is inserted without a value.
This is done on insert only. If you modify the default during the life of the table, the new default will be applied from that moment on. Now how do you make sure a default is applied to columns already NULL? It can for instance be used to build a decision table. Consider the following decision table:. The column in our table just holds the code instead of the value. If we want to represent the value instead of the code we could write a query like this:.
Table Conditions Containing Nulls. For the truth tables showing the results of logical conditions containing nulls, see Table , Table , and Table Do not use null to represent a value of zero, because they are not equivalent. Note: Oracle Database currently treats a character value with a length of zero as null. However, this may not continue to be true in future releases, and Oracle recommends that you do not treat empty strings the same as nulls. Is the criteria "not likely to be found" sufficient?
What happens when an 'unlikely' value appears on either side of the equality test. Is it now acceptable to match a NULL with a an 'unlikely' value? This falls apart if either value could legitimately be -1, and then you'll be pulling out your hair to find the bug. JosephStyons JosephStyons If 0 is something that can occur in your data or in the search value, then you need to use a different dummy value. If you can't come up with a dummy value that is appropriate, you can't use this approach.
You have no need to use this approach at all. There's no reason to compare to dummy values when you can compare directly to actual NULL. Pseudocode follows. I don't think you could use a bind variable here without defeating your purpose — user Ted Ted 1, 1 1 gold badge 11 11 silver badges 5 5 bronze badges. The resolution of this comment is left as an exercise to the reader ;- — DCookie.
I don't get the downvotes. Is the answer incorrect? If so, have the courtesy to state your objections. Perhaps I could adjust my answer to address them. As for the original comment, this was a conceptual illustration. I thought it was pretty clear that one should use a value that won't appear in your data This can also do the job in Oracle.
EvilTeach EvilTeach Does Oracle allow that to work? Ya, I've used it in oracle successfully. I'd like to change my downvote sorry about my hastiness to an upvote which I can't do unless you edit your answer.
I haven't done a formal investigation into all datatypes. I would think that what you have is OK. Carl Carl 5, 4 4 gold badges 24 24 silver badges 23 23 bronze badges. Damnit, I remember that little bit of stupidity now! I think that I'll leave this answer as a reminder to anyone else — Carl. Jason Winger Jason Winger 1.
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