为此，您可以使用子查询。让我们先创建一个表 - mysql> create table DemoTable -> ( -> Value int -> ); 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 DemoTable values(20); Query OK, 1 row affected (0.23 sec) mysql> insert into DemoTable values(30); Query OK, 1 row affected (0.36 sec) mysql> insert into DemoTable values(20); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable values(40); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable values(30); Query OK, ... 阅读更多

让我们先创建一个表 - mysql> create table DemoTable -> ( -> LastName varchar(100) -> ); Query OK, 0 rows affected (0.68 sec)使用 insert 命令在表中插入一些记录 - mysql> insert into DemoTable values('Smith'); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable values('Miller'); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable values('Taylor'); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable values('Brown'); Query OK, 1 row affected (0.29 sec)使用 select 语句显示表中的所有记录 - mysql> select *from DemoTable; 输出 这将产生 ... 阅读更多

让我们先创建一个表 - mysql> create table DemoTable -> ( -> Value int -> ); Query OK, 0 rows affected (0.57 sec)使用 insert 命令在表中插入一些记录 - mysql> insert into DemoTable values(0x41); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable values(0x30); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable values(0x61); Query OK, 1 row affected (0.27 sec)使用 select 语句显示表中的所有记录 - mysql> select *from DemoTable; 输出 这将产生以下输出 -+-------+ | Value | +-------+ | 65 | | ... 阅读更多

为此，您可以使用 SHOW VARIABLES 命令 - mysql> SHOW VARIABLES LIKE 'auto_inc%'; 输出 这将产生以下输出 -+--------------------------+-------+ | Variable_name | Value | +--------------------------+-------+ | auto_increment_increment | 1 | | auto_increment_offset | 1 | +--------------------------+-------+ 2 rows in set (0.95 sec)您可以控制 AUTO_INCREMENT 的外部。让我们先创建一个表 - mysql> create table DemoTable -> ( -> StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY -> ); Query OK, 0 rows affected (0.94 sec)使用 insert 命令在表中插入一些记录 - mysql> insert into DemoTable ... 阅读更多

为此，请使用 ORDER BY DESC 和 LIMIT 1。让我们先创建一个表 - mysql> create table DemoTable -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> UserName varchar(100), -> UserMessage text -> ); Query OK, 0 rows affected (1.17 sec)使用 insert 命令在表中插入一些记录 - mysql> insert into DemoTable(UserName, UserMessage) values('Adam', 'Hi'); Query OK, 1 row affected (0.92 sec) mysql> insert into DemoTable(UserName, UserMessage) values('Chris', 'Awesome'); Query OK, 1 row affected (0.52 sec) mysql> insert into DemoTable(UserName, UserMessage) values('Robert', 'Nice'); Query OK, 1 row affected (0.65 sec) ... 阅读更多

使用 IS NOT NULL 来显示只有非 NULL 记录。让我们先创建一个表 - mysql> create table DemoTable -> ( -> FirstName varchar(100) -> ); Query OK, 0 rows affected (3.01 sec)使用 insert 命令在表中插入一些记录 - mysql> insert into DemoTable values('John'); Query OK, 1 row affected (0.44 sec) mysql> insert into DemoTable values(NULL); Query OK, 1 row affected (0.58 sec) mysql> insert into DemoTable values('Chris'); Query OK, 1 row affected (0.31 sec) mysql> insert into DemoTable values(NULL); Query OK, 1 row affected (0.20 sec) mysql> insert into ... 阅读更多

让我们先创建一个表 - mysql> create table DemoTable -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> Name varchar(100), -> Subject varchar(100), -> Score int -> ); Query OK, 0 rows affected (0.94 sec)使用 insert 命令在表中插入一些记录 - mysql> insert into DemoTable(Name, Subject, Score) values('Chris', 'MySQL', 80); Query OK, 1 row affected (0.32 sec) mysql> insert into DemoTable(Name, Subject, Score) values('Robert', 'MongoDB', 45); Query OK, 1 row affected (0.62 sec) mysql> insert into DemoTable(Name, Subject, Score) values('Adam', 'Java', 78); Query OK, 1 row affected ... 阅读更多

使用 MySQL 中的 ISNULL()。让我们先创建一个表 - mysql> create table DemoTable -> ( -> Number1 int, -> Number2 int -> ); Query OK, 0 rows affected (0.59 sec)使用 insert 命令在表中插入一些记录 - mysql> insert into DemoTable values(10, NULL); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable values(NULL, NULL); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable values(29, 98); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable values(NULL, 119); Query OK, 1 row affected (0.15 sec)显示所有记录 ... 阅读更多

是的，您可以使用 ORDER BY DESC 和 GROUP BY。让我们先创建一个表 - mysql> create table DemoTable -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> PostMessage varchar(100) -> ); Query OK, 0 rows affected (0.69 sec)使用 insert 命令在表中插入一些记录 - mysql> insert into DemoTable(PostMessage) values('Hi'); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable(PostMessage) values('Hello'); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable(PostMessage) values('Hi'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable(PostMessage) values('Awesome'); Query OK, ... 阅读更多

让我们创建一个存储过程，并从MySQL预处理语句中选择返回值：