让我们首先创建一个表 −mysql> create table DemoTable1 (    Name varchar(100),    Gender ENUM('MALE', 'FEMALE') ); Query OK, 0 rows affected (0.50 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable1 values('Chris', 'Male'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable1 values('Emma', 'Female'); Query OK, 1 row affected (0.19 sec)使用 select 语句显示表中的所有记录 −mysql> select *from DemoTable1;这将产生以下输出 −+-------+--------+ | Name  | Gender | +-------+--------+ | Chris | MALE   | | Emma  | FEMALE | +-------+--------+ 2 rows in set ... 阅读更多

让我们首先创建一个表 −mysql> create table DemoTable (    Name varchar(100),    Age int ); Query OK, 0 rows affected (0.46 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable values('Chris', 23); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable values('David', 55); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable values('Bob', 53); Query OK, 1 row affected (0.21 sec) mysql> insert into DemoTable values('Mike', 54); Query OK, 1 row affected (0.24 sec) mysql> insert into DemoTable values('Sam', 55); Query OK, 1 row affected (0.18 sec)显示所有记录 ... 阅读更多

让我们首先创建一个表 −mysql> create table DemoTable (    Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    FirstName varchar(100) ); Query OK, 0 rows affected (0.46 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable(FirstName) values('Chris'); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable(FirstName) values('Robert'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable(FirstName) values('Robert'); Query OK, 1 row affected (0.07 sec) mysql> insert into DemoTable(FirstName) values('John'); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable(FirstName) values('John'); Query OK, 1 row affected (0.11 sec) mysql> insert ... 阅读更多

让我们首先创建一个表 −mysql> create table DemoTable (    FirstName varchar(100),    LastName varchar(100) ); Query OK, 0 rows affected (0.76 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable values('Chris', 'Brown'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable values('Adam', 'Smith'); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable values('Carol', 'Taylor'); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable values('David', 'Miller'); Query OK, 1 row affected (0.12 sec)使用 select 语句显示表中的所有记录 −mysql> select *from DemoTable;这将产生 ... 阅读更多

要更新值为 NULL 的字段，请将 IS NULL 属性与 UPDATE 命令一起使用。让我们首先创建一个表 −mysql> create table DemoTable (    StudentScore int ); Query OK, 0 rows affected (0.47 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable values(89); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable values(NULL); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable values(45); Query OK, 1 row affected (0.09 sec) mysql> insert into DemoTable values(NULL); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable values(56); ... 阅读更多

要使用两个 SELECT 语句将值从第一个表插入到另一个表，请使用子查询。这将允许您仅使用单个 MySQL 查询在第二个表中获取结果。让我们首先创建一个表 −mysql> create table DemoTable1 (    Name varchar(100),    Score int ); Query OK, 0 rows affected (1.30 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable1 values('Chris', 45); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable1 values('Bob', 78); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable1 values('David', 98); ... 阅读更多

为此，让我们首先创建一个表 −mysql> create table DemoTable (    Message text ); Query OK, 0 rows affected (1.15 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable values('Good'); Query OK, 1 row affected (0.43 sec) mysql> insert into DemoTable values('Bye'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable values('Awesome'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable values('Bye'); Query OK, 1 row affected (0.08 sec) mysql> insert into DemoTable values('Good'); Query OK, 1 row affected (0.23 sec) mysql> insert into DemoTable values('Amazing'); Query OK, 1 ... 阅读更多

要在 MySQL 中设置默认值，您需要使用 DEFAULT 关键字。让我们首先创建一个表 −mysql> create table DemoTable (    ClientCountryName varchar(100) DEFAULT 'NONE' ); Query OK, 0 rows affected (0.65 sec)我们已在上面为插入时未输入的值设置了 DEFAULT。现在，让我们使用 insert 命令在表中插入一些记录。我们在这里没有为某些行插入值。DEFAULT 在那里被设置 −mysql> insert into DemoTable values('US'); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable values(); Query OK, 1 row affected (0.09 sec) ... 阅读更多

要从字符串左侧获取一定数量的字符，请在 MySQL 中使用 LEFT 方法。让我们首先创建一个表 −mysql> create table DemoTable (    Name varchar(100) ); Query OK, 0 rows affected (6.58 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable values('Sam Brown'); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable values('David Miller'); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable values('Adam Smith'); Query OK, 1 row affected (7.01 sec) mysql> insert into DemoTable values('Carol Taylor'); Query OK, 1 row affected (0.68 sec)显示所有 ... 阅读更多

是的，我们可以在 MySQL 查询中使用 SELECT NULL 语句。让我们首先创建一个表 −mysql> create table DemoTable (    Name varchar(100) ); Query OK, 0 rows affected (0.49 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable values('Chris'); Query OK, 1 row affected (0.47 sec) mysql> insert into DemoTable values('Mike'); Query OK, 1 row affected (0.23 sec) mysql> insert into DemoTable values('Sam'); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable values('Bob'); Query OK, 1 row affected (0.27 sec) mysql> insert into DemoTable values('David'); Query OK, 1 row affected ... 阅读更多