Friday, October 8, 2010

PL/SQL - Operator Precedence

Hi all, It has been almost an year since I posted a topic in this blog. After a 1 year study break, I back to my usual job and hopfully I am become regular in this blog again.


In SQL or PL/SQL we use several operators. Some are mathematical, logical and comparison operatiors. Oracle follow a order of precedence when execute an expression that contains more than one operators. If operatiors with same precidence are occured then it does not follow any order. Otherwise Oracle maintain the following order of precedence of operators.


Order |------------| Operator |------------| Operation
1 |------------| ** |------------| exponentiation
2 |------------| +, |------------| identity, negation
3 |------------| *, / |------------| multiplication, division
4 |------------| +, -, || |------------| addition, subtraction, concatenation
5 |------------| =, <, >, <=, >=, |------------| comparison
<>, !=, ~=, ^=, IS NULL, LIKE,
BETWEEN, IN
6 |------------| NOT |------------| logical negation
7 |------------| AND |------------| conjunction
8 |------------| OR |------------| inclusion


For example, when NOT, AND and OR operators are used in the same statement NOT is evaluated first, then AND and finally OR.
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