MySQL 논리 연산자

Logical Operators 

논리연산자쯤 되겠지.

Name	Description
AND, &&	Logical AND
NOT, !	Legates value
OR, ||	Logical OR
XOR	Logical XOR

 

In SQL, all alogical operators evaluates to TRUE, FALSE, or NULL (UNKNOWN). In MySQL, these are implemented as 1(TRUE), 0(FALSE), and NULL. Most of this is common to different SQL database aserver, although some servers may return any nonzero value for TRUE.

 

MySQL evaluates any nonzero, non-NULL values to TRUE, 

 

 

1. NOT, !

Logical NOT.

Evalutes to 1 if the operand is 0, to 0 if the operand is nonzero, and NOT NULL.

 

mysql>SELECT NOT 10;

   --> 0

mysql>SELECT NOT 0;

   --> 1

mysql>SELECT NOT NULL;

   --> NULL

mysql>SELECT ! (1+1);

   --> 0

mysql>SELECT ! 1+1;

   --> 1

 

The last exapmle produces 1 because the rexpression evaluages the same way as (!1)+1.

 

The !, operator is a nonstandard MYSQL extension, As of MySQL 8.0.17, this operator is deprecated and support for it will be removed in a future MySQL version. Applicatios should be adjusted to use the standard SQL NOT operator.

 

! 보다는 NOT을 쓰자

 

2. AND, &&

Logical AND.

Evaluates to 1 if all operands are nonzero and not NULL, to 0 if one or more operands are 0, otherwise NULL is returned. 

 

mysql>SELECT 1 AND 1;

   --> 1

mysql>SELECT 1 AND 0;

   --> 0

mysql>SELECT 1 AND NULL;

   --> NULL

mysql>SELECT 0 AND NULL;

   --> 0

mysql>SELECT NULL AND 0;

   --> 0

 

3. OR , ||

Logical OR.

When both operands are non-NULL, the result is 1 if any operand is nonzero, and 0 otherwise. with a NULL operand, the result is 1 if the other operand is nonzero, and NULL otherwise. If both operands are NULL, the result is NULL.

 

mysql>SELECT 1 OR 1;

   --> 1

mysql>SELECT 1 OR 0;

   --> 1

mysql>SELECT 0 OR 0;

   --> 1

mysql>SELECT 0 OR NULL;

   --> NULL

mysql>SELECT 1 OR NULL;

   --> 1

4. XOR

Logical XOR.

Returns NULL if either operand is NULL. For non-NULL operands, evaluages to 1 if an odd number of operands is nonzero, otherwise 0 is returned.

 

mysql>SELECT 1 XOR 1;

   --> 0

mysql>SELECT 1 XOR 0;

   --> 1

mysql>SELECT 1 XOR NULL;

   --> NULL

mysql>SELECT 1 XOR 1 XOR 1;

   --> 1

 

a XOR b is mathematically equal to ( a AND (NOT b)) OR ((NOT a) AND b).

 

흠.. 이거는 보기는 많이 봤지만... 정말 써본적은 한번도 없는 것 같다.