6.3: MySQL
MySQL 1 (, TRUE), 0 (, FALSE) NULL ( ). . , , .
MySQL , :
- , NULL, NULL, <=>;
- , ;
- , ;
- , ;
- TIMESTAMP DATETIME, , timestamp , ;
- ().
, ( ISO-8859-1 Latin1, ).
:
mysql> SELECT 1 > "6x";
-> 0
mysql> SELECT 7 > "6x";
-> 1
mysql> SELECT 0 > "x6";
->'0
mysql> SELECT 0 = "x6";
-> 1
(=):
mysql> select 1 = 0;
-> 0
mysql> select "0" = 0;
-> 1
mysql> select 0.0' = 0;
-> 1
mysql> select '0.01' ='0;
-> 0
mysql> select ".01" = 0.01;
-> 1
He (<> ! =):
mysql> select ".01" <> "0.01:
-> 1
mysql> select .01 <> "0.01"
-> 0
mysql> select "zapp" <> "zappp"
-> 1
, (<=):
mysql> select 0.1 <= 2;
-> 1
, (<):
mysql> select 2 < 2;
-> 0
, (>=):
mysql> select 2 >= 2;
-> 1
, (>):
mysql> select 2 > 2;
-> 0
Null (<=>):
mysql> select 1 <=> 1, NULL <=> NULL, 1 <=> NULL;
->1 1 0
IS NULL IS NOT NULL.
, NULL:
mysql> select 1 IS NULL, 0 IS NULL, NULL IS NULL;
->0 0 1
mysql> select 1 IS NOT NULL, 0 IS NOT NULL, NULL IS NOT NULL;
->1 1 0
expr BETWEEN min AND max.
expr min, max, BETWEEN 1, 0. (min <= expr AND expr <= max), . () , , :
- r TIMESTAMP, DATE DATETIME, MIN() () , ;
- r , , ;
- r , , ;
- r , ;
- , .
mysql> select 1 BETWEEN 2 AND 3;
-> 0
mysql> select "b" BETWEEN "a" AND "c";
-> 1
mysql> select 2 BETWEEN 2 AND "3";
-> 1
mysql> select 2 BETWEEN 2 AND "x-3";
-> 0
expr IN (value,...).
1, expr IN, 0. - , r . . , IN , IN . r - , :
mysql> select 2 IN (0,3,5,'wefwf');
-> 0
mysql> select "wefwf IN (0,3,5,'wefwf');
-> 1
expr NOT IN (value,...)
NOT (expr IN (value,...)).
ISNULL(expr).
expr NULL, ISNULL() 1, 0:
mysql> select ISNULL(1+1);
-> 0
mysql> select ISNULL(1/0);
-> 1
, NULL, =, false!
COALESCE(list).
-NULL :
mysql> select COALESCE(NULL,1);
-> 1
mysql> select COALESCE(NULL,NULL,NULL);
-> NULL
INTERVAL(N,N1,N2,N3,...)
0, N < N1, 1, N < N2 . . , : N1 < N2 < N3 < ... < Nn , . , ( ):
mysql> select INTERVAL(23, 1, 15, 17, 30, 44, 200);
-> 3
mysql> select INTERVAL(10, 1, 10, 100, 1000);
-> 2
mysql> select INTERVAL(22, 23, 30, 44, 200);
-> 0
(=, <>..., LIKE), .
mysql> select "" = ";
-> 1
