mysql> select substring("xiaosong",2);
+-------------------------+
| substring("xiaosong",2) |
+-------------------------+
| iaosong                 |
+-------------------------+
1 row in set (0.00 sec)

mysql> select substring("xiaosong",2,4);
+---------------------------+
| substring("xiaosong",2,4) |
+---------------------------+
| iaos                      |
+---------------------------+
1 row in set (0.00 sec)

mysql> select strcmp("11","bb");
+-------------------+
| strcmp("11","bb") |
+-------------------+
|                -1 |
+-------------------+
1 row in set (0.00 sec)

mysql> select strcmp("bb","bb");
+-------------------+
| strcmp("bb","bb") |
+-------------------+
|                 0 |
+-------------------+
1 row in set (0.00 sec)

mysql> select strcmp("ba","bb");
+-------------------+
| strcmp("ba","bb") |
+-------------------+
|                -1 |
+-------------------+
1 row in set (0.00 sec)

mysql> select strcmp("11",11);
+-----------------+
| strcmp("11",11) |
+-----------------+
|               0 |
+-----------------+
1 row in set (0.00 sec)

mysql> select strcmp(11,11);
+---------------+
| strcmp(11,11) |
+---------------+
|             0 |
+---------------+
1 row in set (0.00 sec)

mysql> select mysql 英文字符串,
    -> length('mysql') mysql的长度;
ERROR 1054 (42S22): Unknown column 'mysql' in 'field list'
mysql> select 'mysql' 英文字符串,
    -> length('mysql') mysql字符串的长度;
+------------+-------------------+
| 英文字符串 | mysql字符串的长度 |
+------------+-------------------+
| mysql      |                 5 |
+------------+-------------------+
1 row in set (0.00 sec)

mysql> select find_in_set("33","1,3,4,55,44");
+---------------------------------+
| find_in_set("33","1,3,4,55,44") |
+---------------------------------+
|                               0 |
+---------------------------------+
1 row in set (0.00 sec)

mysql> select find_in_set("33","1,3,33,4,55,44");
+------------------------------------+
| find_in_set("33","1,3,33,4,55,44") |
+------------------------------------+
|                                  3 |
+------------------------------------+
1 row in set (0.00 sec)

mysql> select find_in_set("55","1,3,33,4,55,44");
+------------------------------------+
| find_in_set("55","1,3,33,4,55,44") |
+------------------------------------+
|                                  5 |
+------------------------------------+
1 row in set (0.00 sec)

mysql> select field("song","xiao","zhan","song","yong");
+-------------------------------------------+
| field("song","xiao","zhan","song","yong") |
+-------------------------------------------+
|                                         3 |
+-------------------------------------------+
1 row in set (0.00 sec)

mysql> select field("song","xiao","zhan","yong");
+------------------------------------+
| field("song","xiao","zhan","yong") |
+------------------------------------+
|                                  0 |
+------------------------------------+
1 row in set (0.00 sec)

mysql> select position("song" in "xiaosong") 位置,
    -> locate("song","xiaosong") 位置,
    -> instr("song","xiaosong") 位置;
+------+------+------+
| 位置 | 位置 | 位置 |
+------+------+------+
|    5 |    5 |    0 |
+------+------+------+
1 row in set (0.00 sec)

mysql> select position("song" in "xiaosong") 位置,
    -> locate("song","xiaosong") 位置,
    -> instr("xiaosong","song") 位置;
+------+------+------+
| 位置 | 位置 | 位置 |
+------+------+------+
|    5 |    5 |    5 |
+------+------+------+
1 row in set (0.00 sec)

mysql> select replace("这是我的mysql服务器","mysql","php");
+----------------------------------------------+
| replace("这是我的mysql服务器","mysql","php") |
+----------------------------------------------+
| 这是我的php服务器                            |
+----------------------------------------------+
1 row in set (0.00 sec)

mysql> select abs(10);
+---------+
| abs(10) |
+---------+
|      10 |
+---------+
1 row in set (0.00 sec)

mysql> select abs(-10);
+----------+
| abs(-10) |
+----------+
|       10 |
+----------+
1 row in set (0.00 sec)

mysql> select cell(3.3);
ERROR 1305 (42000): FUNCTION test.cell does not exist
mysql> select ceil(3.3);
+-----------+
| ceil(3.3) |
+-----------+
|         4 |
+-----------+
1 row in set (0.00 sec)

mysql> select floor(3.3);
+------------+
| floor(3.3) |
+------------+
|          3 |
+------------+
1 row in set (0.00 sec)

mysql> select mod(2,3);
+----------+
| mod(2,3) |
+----------+
|        2 |
+----------+
1 row in set (0.00 sec)

mysql> select mod(9,3);
+----------+
| mod(9,3) |
+----------+
|        0 |
+----------+
1 row in set (0.00 sec)

mysql> select mod(7,3);
+----------+
| mod(7,3) |
+----------+
|        1 |
+----------+
1 row in set (0.00 sec)

mysql> select rand()
    -> ;
+--------------------+
| rand()             |
+--------------------+
| 0.2543807385995805 |
+--------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|               6921 |
+--------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|               6974 |
+--------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|               4104 |
+--------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|               9597 |
+--------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|               5675 |
+--------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|               9580 |
+--------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|                877 |
+--------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|               5645 |
+--------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|               5592 |
+--------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|               1025 |
+--------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*1000);
+-------------------+
| ceil(rand()*1000) |
+-------------------+
|               835 |
+-------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*1000);
+-------------------+
| ceil(rand()*1000) |
+-------------------+
|               868 |
+-------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*1000);
+-------------------+
| ceil(rand()*1000) |
+-------------------+
|               833 |
+-------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*1000);
+-------------------+
| ceil(rand()*1000) |
+-------------------+
|               560 |
+-------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|               2991 |
+--------------------+
1 row in set (0.00 sec)

mysql> 
mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|               8176 |
+--------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|               1907 |
+--------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|               5005 |
+--------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|               9306 |
+--------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|               1513 |
+--------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|               9648 |
+--------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|               3698 |
+--------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|               9547 |
+--------------------+
1 row in set (0.00 sec)

mysql> select ceil(rand()*10000);
+--------------------+
| ceil(rand()*10000) |
+--------------------+
|               6640 |
+--------------------+
1 row in set (0.00 sec)

mysql> select truncate(22.333,2);
+--------------------+
| truncate(22.333,2) |
+--------------------+
|              22.33 |
+--------------------+
1 row in set (0.00 sec)

mysql> select truncate(22.339,2);
+--------------------+
| truncate(22.339,2) |
+--------------------+
|              22.33 |
+--------------------+
1 row in set (0.00 sec)

mysql> select round(4.5);
+------------+
| round(4.5) |
+------------+
|          5 |
+------------+
1 row in set (0.00 sec)

mysql> select round(4.3);
+------------+
| round(4.3) |
+------------+
|          4 |
+------------+
1 row in set (0.00 sec)

mysql> select round(4.33333);
+----------------+
| round(4.33333) |
+----------------+
|              4 |
+----------------+
1 row in set (0.00 sec)

mysql> select round(4.33333,1);
+------------------+
| round(4.33333,1) |
+------------------+
|              4.3 |
+------------------+
1 row in set (0.00 sec)

mysql> select round(4.33333,3);
+------------------+
| round(4.33333,3) |
+------------------+
|            4.333 |
+------------------+
1 row in set (0.00 sec)

mysql> select round(4.33333,2);
+------------------+
| round(4.33333,2) |
+------------------+
|             4.33 |
+------------------+
1 row in set (0.00 sec)

mysql> select round(4.33933,2);
+------------------+
| round(4.33933,2) |
+------------------+
|             4.34 |
+------------------+
1 row in set (0.00 sec)

mysql> select curdate();
+------------+
| curdate()  |
+------------+
| 2017-12-19 |
+------------+
1 row in set (0.00 sec)

mysql> select curtime();
+-----------+
| curtime() |
+-----------+
| 21:38:13  |
+-----------+
1 row in set (0.00 sec)

mysql> select now
    -> 
    -> \c
mysql> select now();
+---------------------+
| now()               |
+---------------------+
| 2017-12-19 21:39:15 |
+---------------------+
1 row in set (0.00 sec)

mysql> select date(now());
+-------------+
| date(now()) |
+-------------+
| 2017-12-19  |
+-------------+
1 row in set (0.00 sec)

mysql> select time(now());
+-------------+
| time(now()) |
+-------------+
| 21:39:29    |
+-------------+
1 row in set (0.00 sec)

mysql> select time("2017-12-19 17:33:22");
+-----------------------------+
| time("2017-12-19 17:33:22") |
+-----------------------------+
| 17:33:22                    |
+-----------------------------+
1 row in set (0.00 sec)

mysql> select time("2017-12-19 17:33:22");
+-----------------------------+
| time("2017-12-19 17:33:22") |
+-----------------------------+
| 17:33:22                    |
+-----------------------------+
1 row in set (0.00 sec)

mysql> select week(now());
+-------------+
| week(now()) |
+-------------+
|          51 |
+-------------+
1 row in set (0.00 sec)

mysql> select week("2017-12-16");
+--------------------+
| week("2017-12-16") |
+--------------------+
|                 50 |
+--------------------+
1 row in set (0.00 sec)

mysql> select year("2017-12-16");
+--------------------+
| year("2017-12-16") |
+--------------------+
|               2017 |
+--------------------+
1 row in set (0.00 sec)

mysql> select unix_timestamp(now());
+-----------------------+
| unix_timestamp(now()) |
+-----------------------+
|            1513690980 |
+-----------------------+
1 row in set (0.00 sec)

mysql> select from_unixtime(1513690980);
+---------------------------+
| from_unixtime(1513690980) |
+---------------------------+
| 2017-12-19 21:43:00       |
+---------------------------+
1 row in set (0.00 sec)

mysql> select from_unixtime(1513690989);
+---------------------------+
| from_unixtime(1513690989) |
+---------------------------+
| 2017-12-19 21:43:09       |
+---------------------------+
1 row in set (0.00 sec)

mysql> select now() 当前时间,
    -> select year(now()) 年份,
    -> select quarter(now()) 季度,
    -> select month(now()) 月,
    -> \c
mysql> select now() 当前时间,
    -> year(now()) 年份,
    -> quarter(now()) 季度,
    -> month(now()) 月,
    -> week(now()) 星期周期,
    -> dayofmonth(now()) 天,
    -> hour(now()) 时,
    -> minute(now()) 分,
    -> second(now()) 秒;
+---------------------+------+------+------+----------+------+------+------+------+
| 当前时间            | 年份 | 季度 | 月   | 星期周期 | 天   | 时   | 分   | 秒   |
+---------------------+------+------+------+----------+------+------+------+------+
| 2017-12-19 21:49:51 | 2017 |    4 |   12 |       51 |   19 |   21 |   49 |   51 |
+---------------------+------+------+------+----------+------+------+------+------+
1 row in set (0.00 sec)

mysql> select day(now());
+------------+
| day(now()) |
+------------+
|         19 |
+------------+
1 row in set (0.00 sec)

mysql> select now() 当前时间,
    -> week(now()) 年中的第几个星期,
    -> dayname(now()) 星期,
    -> dayofweek(now()) xingqi,
    -> weekday(now()) 星期;
+---------------------+------------------+---------+--------+------+
| 当前时间            | 年中的第几个星期 | 星期    | xingqi | 星期 |
+---------------------+------------------+---------+--------+------+
| 2017-12-19 21:52:48 |               51 | Tuesday |      3 |    1 |
+---------------------+------------------+---------+--------+------+
1 row in set (0.00 sec)

mysql> select dayofyear(now());
+------------------+
| dayofyear(now()) |
+------------------+
|              353 |
+------------------+
1 row in set (0.00 sec)

mysql> select dayofmonth(now());
+-------------------+
| dayofmonth(now()) |
+-------------------+
|                19 |
+-------------------+
1 row in set (0.00 sec)

mysql> 
mysql> 
mysql> 
mysql> select to_days("2017-06-18 12:22:55");
+--------------------------------+
| to_days("2017-06-18 12:22:55") |
+--------------------------------+
|                         736863 |
+--------------------------------+
1 row in set (0.00 sec)

mysql> select to_days("2017-06-11 18:11:35");
+--------------------------------+
| to_days("2017-06-11 18:11:35") |
+--------------------------------+
|                         736856 |
+--------------------------------+
1 row in set (0.00 sec)

mysql> select to_days("2017-06-18 12:22:55")-to_days("2017-06-11 18:11:35");
+---------------------------------------------------------------+
| to_days("2017-06-18 12:22:55")-to_days("2017-06-11 18:11:35") |
+---------------------------------------------------------------+
|                                                             7 |
+---------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select datediff("2016-12-31","2017-01-05");
+-------------------------------------+
| datediff("2016-12-31","2017-01-05") |
+-------------------------------------+
|                                  -5 |
+-------------------------------------+
1 row in set (0.00 sec)

mysql> select datediff("2017-12-31","2017-01-05");
+-------------------------------------+
| datediff("2017-12-31","2017-01-05") |
+-------------------------------------+
|                                 360 |
+-------------------------------------+
1 row in set (0.00 sec)