一天一点MySQL复习——获取数据库系统时间、变量赋值、变量比较

一、SQL获取系统时间

 1 mysql> select now() from dual;
 2 +---------------------+
 3 | now()               |
 4 +---------------------+
 5 | 2016-05-24 08:34:12 |
 6 +---------------------+
 7 1 row in set (0.00 sec)
 8 mysql> select curdate() from dual;
 9 +------------+
10 | curdate()  |
11 +------------+
12 | 2016-05-24 |
13 +------------+
14 1 row in set (0.01 sec)
15 mysql> select curtime() from dual;
16 +-----------+
17 | curtime() |
18 +-----------+
19 | 08:36:23  |
20 +-----------+
21 1 row in set (0.00 sec)

二、变量赋值

　　select 方式：

　　　　select @name:=value;

 1 mysql> select @b:=4;
 2 +-------+
 3 | @b:=4 |
 4 +-------+
 5 |     4 |
 6 +-------+
 7 1 row in set (0.00 sec)
 8
 9 mysql> select @b;
10 +------+
11 | @b   |
12 +------+
13 |    4 |
14 +------+
15 1 row in set (0.00 sec)

　　　　select row_name from table INTO @name;

 1 mysql> select now() from dual INTO @test1;
 2 Query OK, 1 row affected (0.00 sec)
 3
 4 mysql> select @test1;
 5 +---------------------+
 6 | @test1              |
 7 +---------------------+
 8 | 2016-05-24 08:48:21 |
 9 +---------------------+
10 1 row in set (0.00 sec)

　set方式：

　　　　赋值：set @name:=value;

　　　　　　   set @name=value;

 1 mysql> set @c=1;
 2 Query OK, 0 rows affected (0.00 sec)
 3
 4 mysql> select @c;
 5 +------+
 6 | @c   |
 7 +------+
 8 |    1 |
 9 +------+
10 1 row in set (0.00 sec)
11
12 mysql> set @c:=2;
13 Query OK, 0 rows affected (0.00 sec)
14
15 mysql> select @c;
16 +------+
17 | @c   |
18 +------+
19 |    2 |
20 +------+
21 1 row in set (0.00 sec)

三、变量比较

 1 mysql> select @time1,@time2;
 2 +---------------------+---------------------+
 3 | @time1              | @time2              |
 4 +---------------------+---------------------+
 5 | 2016-05-24 08:54:44 | 2016-05-24 08:27:57 |
 6 +---------------------+---------------------+
 7 1 row in set (0.00 sec)
 8
 9 mysql> select now() from dual INTO @time1;
10 Query OK, 1 row affected (0.00 sec)
11
12 mysql> select now() from dual INTO @time2;
13 Query OK, 1 row affected (0.00 sec)
14
15 mysql> select @time1,@time2;
16 +---------------------+---------------------+
17 | @time1              | @time2              |
18 +---------------------+---------------------+
19 | 2016-05-24 08:58:23 | 2016-05-24 08:58:38 |
20 +---------------------+---------------------+
21 1 row in set (0.00 sec)
22
23 mysql> select @time1 < @time2;
24 +-----------------+
25 | @time1 < @time2 |
26 +-----------------+
27 |               1 |
28 +-----------------+
29 1 row in set (0.00 sec)
30
31 mysql> select @time1 > @time2;
32 +-----------------+
33 | @time1 > @time2 |
34 +-----------------+
35 |               0 |
36 +-----------------+
37 1 row in set (0.00 sec)