Oracle 5.0, Справочное руководство

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Logical Operators
880
This happens because MySQL reads
9223372036854775808.0
in an integer context. The integer
representation is not good enough to hold the value, so it wraps to a signed integer.
12.3.3. Logical Operators
Table 12.4. Logical Operators
Name Description
AND
,
&&
[880] Logical AND
NOT
,
!
[880] Negates value
||
,
OR
[881] Logical OR
XOR
[881] Logical XOR
In SQL, all logical operators evaluate 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
servers, although some servers may return any nonzero value for
TRUE
.
MySQL evaluates any nonzero, non-
NULL
value to
TRUE
. For example, the following statements all
assess to
TRUE
:
mysql> SELECT 10 IS TRUE;
-> 1
mysql> SELECT -10 IS TRUE;
-> 1
mysql> SELECT 'string' IS NOT NULL;
-> 1
•
NOT
[880] ,
!
[880]
Logical NOT. Evaluates to
1
if the operand is
0
, to
0
if the operand is nonzero, and
NOT NULL
returns
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 example produces
1
because the expression evaluates the same way as
(!1)+1
.
Note that the precedence of the
NOT
[880] operator changed in MySQL 5.0.2. See Section 12.3.1,
“Operator Precedence” .
•
AND
[880] ,
&&
[880]
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 && 1;
-> 1
mysql> SELECT 1 && 0;
-> 0
mysql> SELECT 1 && NULL;
-> NULL
mysql> SELECT 0 && NULL;
-> 0
mysql> SELECT NULL && 0;
-> 0