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:. The case statement has two flavors. The simple case and the searched case. In the simple case the expression is written only once and depending on the result of this expression one of the possible cases is being used.
This can be helpful when you need to choose from a set of distinct values. In the searched case every case has its own expression. This can for instance be helpful when using ranges. The else clause is optional. NULL values are one of the most mind-boggling values in the Oracle database. Viewed 10k times. How do I set an empty set or null value to a default value like 1? Improve this question. Mangesh Pimpalkar 3, 2 2 gold badges 30 30 silver badges 52 52 bronze badges. Where do you suppose to get null values?
How can I set an empty set to a value of 1? Add a comment. Active Oldest Votes. Improve this answer. I doubt there is any difference in performance. Mangesh Pimpalkar Mangesh Pimpalkar 3, 2 2 gold badges 30 30 silver badges 52 52 bronze badges.
Because null represents a lack of data, a null cannot be equal or unequal to any value or to another null. Oracle also considers two nulls to be equal if they appear in compound keys. That is, Oracle considers identical two compound keys containing nulls if all the non-null components of the keys are equal.
Table shows examples of various evaluations involving nulls in conditions. Table Conditions Containing Nulls.
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