是的，我们可以这样做。语法如下：语法 1：select * from yourTableName1, yourTableName2; 语法 2：select * from yourTableName1 cross join yourTableName2;以上两种语法产生相同的结果。让我们首先创建一个表：mysql> create table DemoTable1882    (    Id int    ); Query OK, 0 rows affected (0.00 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable1882 values(10); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1882 values(20); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1882 values(30); Query OK, 1 row affected (0.00 sec)显示所有记录 ... 阅读更多

要对数字字符串使用比较运算符，请使用 substring() 方法。让我们首先创建一个表：mysql> create table DemoTable1881    (    UserId int,    UserEducationGap varchar(20)    ); Query OK, 0 rows affected (0.00 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable1881 values(101, '5-9'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1881 values(102, '2-4'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1881 values(103, '4-8'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1881 values(104, '7-12'); Query OK, 1 row affected (0.00 sec)显示所有记录 ... 阅读更多

为此，请使用 INSERT INTO SELECT 语句。让我们首先创建一个表：mysql> create table DemoTable1879    (    Id int,    Name varchar(20)    ); Query OK, 0 rows affected (0.00 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable1879 values(101, 'Chris Brown'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1879 values(102, 'David Miller'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1879 values(103, 'Adam Smith'); Query OK, 1 row affected (0.00 sec)使用 select 语句显示表中的所有记录：mysql> select * from DemoTable1879;这将产生 ... 阅读更多

使用 IFNULL() 查找并为 NULL 值放置特定值。让我们首先创建一个表：mysql> create table DemoTable1878    (    FirstName varchar(20)    ); Query OK, 0 rows affected (0.00 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable1878 values('Chris'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1878 values(NULL); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1878 values('David'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1878 values(NULL); Query OK, 1 row affected (0.00 sec)使用 select 语句显示表中的所有记录 ... 阅读更多

让我们首先创建一个表：mysql> create table DemoTable1877 ( DueDate datetime ); Query OK, 0 rows affected (0.00 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable1877 values('2019-12-10'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1877 values('2019-12-05'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1877 values('2019-12-07'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1877 values('2019-12-09'); Query OK, 1 row affected (0.00 sec)使用 select 语句显示表中的所有记录：mysql> select * from DemoTable1877;这将 ... 阅读更多

让我们首先创建一个表：mysql> create table DemoTable1875    (    Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    Class varchar(20),    Amount int ); Query OK, 0 rows affected (0.00 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable1875(Class, Amount) values('X', 750); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1875(Class, Amount) values('X', 140); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1875(Class, Amount) values('X', 450); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1875(Class, Amount) values('Y', 6780); Query OK, 1 row affected (0.00 ... 阅读更多

为此，请使用带有 UPDATE 命令的 CASE 语句。让我们首先创建一个表：mysql> create table DemoTable1874    (    Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    Amount varchar(100) ); Query OK, 0 rows affected (0.00 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable1874(Amount) values('3450'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1874(Amount) values('190'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1874(Amount) values('7600'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1874(Amount) values('4500'); Query OK, 1 row affected (0.00 sec)显示所有记录 ... 阅读更多

要更新单个列，请使用 UPDATE 和 SET，如下面的语法所示：update yourTableName set yourColumnName=yourValue;让我们首先创建一个表：mysql> create table DemoTable1873      (      Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,      FirstName varchar(20)      ); Query OK, 0 rows affected (0.00 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable1873(FirstName) values('John'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1873(FirstName) values('Adam'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1873(FirstName) values('David'); Query OK, 1 row affected (0.00 sec) mysql> insert into ... 阅读更多

为此，请使用 SUBSTRING()。让我们首先创建一个表：mysql> create table DemoTable1872    (    Name varchar(20)    ); Query OK, 0 rows affected (0.00 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable1872 values('John Doe'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1872 values('Adam Smith'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1872 values('Mitchell Johnson'); Query OK, 1 row affected (0.00 sec)使用 select 语句显示表中的所有记录：mysql> select * from DemoTable1872;这将产生以下输出：+------------------+ | Name         ... 阅读更多

让我们首先创建一个表：mysql> create table DemoTable1871      (      ArrivalDate datetime      ); Query OK, 0 rows affected (0.00 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable1871 values('2019-12-19 7:45:00'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1871 values('2018-11-10 12:00:00'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1871 values('2019-01-31'); Query OK, 1 row affected (0.00 sec)使用 select 语句显示表中的所有记录：mysql> select * from DemoTable1871; 这将产生以下输出：+---------------------+ | ArrivalDate         | ... 阅读更多