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7 lut 2012 · 9 Answers. Sorted by: 65. COUNT(expresion) returns the count of of rows where expresion is not null. So SELECT COUNT (COL_NAME) FROM TABLE WHERE COL_NAME IS NULL will return 0, because you are only counting col_name where col_name is null, and a count of nothing but nulls is zero.
Nulls can appear in columns of any data type that are not restricted by NOT NULL or PRIMARY KEY integrity constraints. Use a null when the actual value is not known or when a value would not be meaningful. Oracle Database treats a character value with a length of zero as null.
In this tutorial, you will learn how to use the Oracle IS NULL and IS NOT NULL operators to check if a value in a column or an expression is NULL or not.
Null functions. Oracle Database includes many functions to help you handle nulls. NVL and coalesce are two that map nulls to non-null values. NVL. This takes two arguments. If the first is null, it returns the second: select toy_name, volume_of_wood, nvl ( volume_of_wood , 0 ) mapped_volume_of_wood from toys; Coalesce. This is like NVL.
30 sie 2012 · What is NULL? NULL is nothing. NULL is not even the same as NULL. NULL is undefined. But you need to work with NULL values (which are no actual values). Luckily Oracle provides us with a couple of functions to do the heavy lifting when it comes to checking for NULLs. IS [NOT] NULL. Syntax: 1. expr1IS[NOT]NULL.
The NVL function allows you to replace null values with a default value. If the value in the first parameter is null, the function returns the value in the second parameter. If the first parameter is any value other than null, it is returned unchanged. We know that COL1 in the test table contains null in all rows except the first.
In oracle you can join null values using decode: SELECT * FROM T1 JOIN T2 ON DECODE(T1.SOMECOL, T2.SOMECOL, 1, 0) = 1 decode treats nulls as equal, so this works without "magic" numbers.
