Oracle expression Operator Precedence

Oracle has the following types of operators

Arithmetic operator join operator comparison (relational) operator logical operator

1. Arithmetic operators

The arithmetic operator has four, +,-, *,/.

SELECT sal,sal* from EMP;    The value after #sal and sal*12.

2. Connection operators

The Join operator has | | You can concatenate two of strings together.

SELECT ename | | "The Wages are" | | Sal from EMP;   #此 | | is to connect employees to wages         Bob (ename) "Wages are" (SAL)

3. Compare (relational) operators

The relational operators are > greater than, >= is greater than or equal, < less than, <= is less than or equal,! = or <> is not equal.

Selcet  ename,sal,hiredate from     emp WHERE    '01-jan-91';                #找出1991年01月01日日期以后的记录.

Special relational operator "between and" "in" "like"

Between and selects a range of records. Cases:

SELECT ename,sal from  emp  WHERE sal  ;        #sal列下1500-3000 of records.

In to intercept multiple records. Cases:

SELECT ename,sal,hiredate,job  from emp WHERE job  in (' Salesman ','clerak',  'MANAGER');   The #选取 job value is ' salesman ','clerak','MANAGER' records.

Like in conjunction with wildcard match examples:

' sal% ';   #% can be understood as a wildcard character, which is equivalent to the * number. Represents any character.

% represents 0 or more characters

_ Represents a single character example:

' s_l_s% ';   #第一个字符为S, the second is an L, and the third is an arbitrary value of S.

If the matched value contains a% or _, it can be escaped. Cases:

CREATE TABLE test_dept as SELECT * from dept;  #新建一张测试表. INSERT into Test_dept VALUES ("it_rese",'Beijing  ');    ' it\_% '  ' \ ';   #escape defines the escape character. 

4. Logical operators

logical operators have and (logical AND) or (logical OR) not (logical not)

T is true, F is false and expression is expression 1 and expression 2 expression one or two both have a result of T and no is f.

F and F = f f and t = f t and T =t

and Priority f>null>t

or expression 1 or expression 2 only one of the expressions is true, and the result is true.

F or F =f f or T = t t or T = t

OR Priority T->null>f

The result is true when the not expression 1 not expression 22 edge condition is not valid

F not F =t f not t = f t t = f

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Operator Precedence

Arithmetic operator > Join operator > Relational operator >is null,is not NULL, like, not-like, in, not-in operator >between, not between operator >not logical operator &G T The and logical operator >or logical operators. Cases:

SELECT ename,empno,sal,job from  emp WHERE job='clerk'job   ='  Salesman' and sal>=;   #AND expression is prioritized and will be calculated first.

NULL indicates null, not equal to a space, the expression contains null, and the result is null

　　

Oracle expression Operator Precedence