要在 MySQL 中按日期分组，请使用 GROUP BY 子句 −mysql> create table DemoTable2002 (    CustomerName varchar(20),    CustomerShippingDate datetime ); Query OK, 0 rows affected (0.61 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable2002 values('Chris', '2019-01-10'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable2002 values('David', '2018-12-31'); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable2002 values('David', '2019-12-16'); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable2002 values('Chris', '2018-12-01'); Query OK, 1 row affected (0.12 sec)使用 select 语句显示表中的所有记录 −mysql> select * ... 阅读更多

要使用用户定义变量获取最大考试日期，代码如下：select date(max(yourColumnName )) into @yourVariableName  from yourTableName;为了理解上述语法，让我们首先创建一个表 −mysql> create table DemoTable2001 (    ExamDate date ); Query OK, 0 rows affected (0.60 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable2001 values('2019-01-10'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable2001 values('2018-12-31'); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable2001 values('2018-11-18'); Query OK, 1 row affected (0.39 sec) mysql> insert into DemoTable2001 values('2019-07-25'); Query OK, 1 ... 阅读更多

要显示正确的单引号，需要使用 COLLATE='utf8_unicode_ci' 修改表。让我们首先创建一个表 −mysql> create table DemoTable2000 (    Name varchar(20) ); Query OK, 0 rows affected (0.81 sec)以下是使用 collate 的查询 −mysql> ALTER TABLE DemoTable2000 COLLATE='utf8_unicode_ci'; Query OK, 0 rows affected (0.90 sec) Records: 0  Duplicates: 0  Warnings: 0使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable2000 values('Chris’s Brown'); Query OK, 1 row affected (0.09 sec) mysql> insert into DemoTable2000 values('David’s Miller'); Query OK, 1 row affected (0.67 sec) mysql> insert into DemoTable2000 values('Robert’s Downey'); Query ... 阅读更多

要仅返回月份名称，可以使用 DATE_FORMAT() −mysql> create table DemoTable1999 (    ArrivalDate timestamp ); Query OK, 0 rows affected (0.66 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable1999 values('2019-01-01 12:34:00'); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable1999 values('2019-12-31 10:04:00'); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable1999 values('2018-10-11 04:04:30'); Query OK, 1 row affected (0.14 sec)使用 select 语句显示表中的所有记录 −mysql> select * from DemoTable1999;这将产生以下输出：+---------------------+ | ArrivalDate         | +---------------------+ ... 阅读更多

要从重复的行中只返回一行，请使用 DISTINCT 关键字 −mysql> create table DemoTable1998 (    Name varchar(20) ); Query OK, 0 rows affected (0.61 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable1998 values('Robert'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable1998 values('Chris'); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable1998 values('Robert'); Query OK, 1 row affected (0.30 sec) mysql> insert into DemoTable1998 values('David'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable1998 values('Bob'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable1998 ... 阅读更多

要将日期转换为 UNIX 时间戳，请在 MySQL 中使用 UNIX_TIMESTAMP() −mysql> create table DemoTable1997 (    DueDate date ); Query OK, 0 rows affected (0.58 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable1997 values('2018-10-11'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable1997 values('2019-12-21'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable1997 values('2017-01-31'); Query OK, 1 row affected (0.11 sec)使用 select 语句显示表中的所有记录 −mysql> select * from DemoTable1997;这将产生以下输出：+------------+ | DueDate    | +------------+ | 2018-10-11 | | 2019-12-21 | ... 阅读更多

让我们创建一个表 −mysql> create table DemoTable1996 (    ShippingDate datetime,    CustomerName varchar(20) ); Query OK, 0 rows affected (0.84 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable1996 values('2019-12-21 10:45:00', 'Chris'); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable1996 values('2019-12-21 12:10:00', 'David'); Query OK, 1 row affected (0.09 sec) mysql> insert into DemoTable1996 values('2019-12-20 12:10:00', 'Bob'); Query OK, 1 row affected (0.14 sec)使用 select 语句显示表中的所有记录 −mysql> select * from DemoTable1996;这将产生以下输出：+---------------------+--------------+ | ShippingDate        | CustomerName ... 阅读更多

让我们首先创建一个表 −mysql> create table DemoTable1994 (    ArrivalDate date ); Query OK, 0 rows affected (5.33 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable1994 values('2019-12-18'); Query OK, 1 row affected (0.47 sec) mysql> insert into DemoTable1994 values('2019-12-19'); Query OK, 1 row affected (0.33 sec) mysql> insert into DemoTable1994 values('2019-12-20'); Query OK, 1 row affected (0.49 sec) mysql> insert into DemoTable1994 values('2019-12-25'); Query OK, 1 row affected (0.30 sec) mysql> insert into DemoTable1994 values('2018-12-20'); Query OK, 1 row affected (1.42 sec)使用 select 语句显示表中的所有记录 −mysql> select ... 阅读更多

使用 if else 为枚举设置自定义消息。让我们首先创建一个表 −mysql> create table DemoTable1992 (    ClientId int NOT NULL AUTO_INCREMENT PRIMARY KEY,    ClientName varchar(20),    isActive ENUM('Y', 'N') ); Query OK, 0 rows affected (0.89 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable1992(ClientName, isActive) values('Chris', 'N'); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable1992(ClientName, isActive) values('Bob', 'N'); Query OK, 1 row affected (0.08 sec) mysql> insert into DemoTable1992(ClientName, isActive) values('David', 'Y'); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable1992(ClientName, isActive) values('Carol', ... 阅读更多

为此，您可以使用 NOT IN() −mysql> create table DemoTable1991 (    StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY,    StudentName varchar(20) ); Query OK, 0 rows affected (0.61 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable1991(StudentName) values('Chris'); Query OK, 1 row affected (0.24 sec) mysql> insert into DemoTable1991(StudentName) values('Bob'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable1991(StudentName) values('David'); Query OK, 1 row affected (0.08 sec) mysql> insert into DemoTable1991(StudentName) values('Sam'); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable1991(StudentName) values('Mike'); Query OK, 1 row affected (0.11 sec)显示所有 ... 阅读更多