错误发生是因为我们在列名的末尾有一个逗号，就在“from tablename”之前。以下是你可能遇到的错误：mysql> select ClientId, ClientName, ClientAge, from DemoTable1391; ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'from DemoTable1391' at line 1要消除错误，如上所述，您需要从表中删除最后一个逗号。让我们首先创建一个：mysql> create table DemoTable1391    -> (    -> ClientId int NOT ... 阅读更多

如果字符串以整数开头，则它会将字符串转换为整数，否则不会。让我们首先创建一个：mysql> create table DemoTable1390    -> (    -> StudentId varchar(20)    -> ); Query OK, 0 rows affected (0.93 sec)使用 insert 在表中插入一些记录：mysql> insert into DemoTable1390 values('563_John'); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable1390 values('1001_Carol_Taylor'); Query OK, 1 row affected (0.08 sec) mysql> insert into DemoTable1390 values('David_Miller_789'); Query OK, 1 row affected (0.07 sec) mysql> insert into DemoTable1390 values('456_AdamSmith'); Query OK, 1 row affected (0.11 sec)显示来自... 阅读更多

让我们首先创建一个：mysql> create table DemoTable1    -> (    -> StudentFirstName varchar(20),    -> StudentLastName varchar(20),    -> StudentAge int,    -> StudentCountryName varchar(20)    -> ); Query OK, 0 rows affected (4.20 sec)现在让我们在 MySQL 中将所有列名转换为小写：mysql> select concat('alter table ', table_name, ' change `', column_name, '` `',    -> lower(column_name), '` ', column_type, ';')    -> from information_schema.columns  where table_schema = 'demo';这将产生以下输出：+-----------------------------------------------------------------------------------------------------------------+ | concat('alter table ', table_name, ' change `', column_name, '` `', lower(column_name), '` ', column_type, ';') | +-----------------------------------------------------------------------------------------------------------------+ | ... 阅读更多

让我们首先创建一个：mysql> create table DemoTable1620    -> (    -> Subject varchar(20)    -> ); Query OK, 0 rows affected (0.42 sec)使用 insert 在表中插入一些记录：mysql> insert into DemoTable1620 values('mysql'); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable1620 values('MySql'); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable1620 values('mYSQL'); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable1620 values('MySQL'); Query OK, 1 row affected (0.26 sec) mysql> insert into DemoTable1620 values('MYSQL'); Query OK, 1 row affected (0.20 sec)使用 select ... 阅读更多

为此，使用连接概念。让我们首先创建一个：mysql> create table DemoTable1389    -> (    -> StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY,    -> StudentMarks int    -> ); Query OK, 0 rows affected (2.73 sec)使用 insert 命令在表中插入一些记录。在这里，我们也插入了重复的值：mysql> insert into DemoTable1389(StudentMarks) values(40); Query OK, 1 row affected (0.26 sec) mysql> insert into DemoTable1389(StudentMarks) values(40); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable1389(StudentMarks) values(68); Query OK, 1 row affected (0.25 sec) mysql> insert into DemoTable1389(StudentMarks) values(78); Query OK, ... 阅读更多

以下是语法：select * from yourViewName;让我们首先创建一个表：mysql> create table DemoTable1388    -> (    -> StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY,    -> StudentName varchar(40)    -> ); Query OK, 0 rows affected (0.71 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable1388(StudentName) values('Chris'); Query OK, 1 row affected (0.23 sec) mysql> insert into DemoTable1388(StudentName) values('Bob'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable1388(StudentName) values('David'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable1388(StudentName) values('Mike'); Query OK, 1 row affected (0.29 sec)显示所有... 阅读更多

要合并，请使用 GROUP_CONCAT() 函数将两行中的一些属性合并为一行。作为分隔符，使用连字符。让我们首先创建一个表：mysql> create table DemoTable1386    -> (    -> Title varchar(255),    -> Name varchar(60)    -> ); Query OK, 0 rows affected (0.67 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable1386 values('Introduction to MySQL', 'Paul DuBois'); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable1386 values('Java in Depth', 'Khalid Mughal'); Query OK, 1 row affected (0.48 sec) mysql> insert into DemoTable1386 values('Introduction to MySQL', 'Russell Dyer'); Query OK, ... 阅读更多

要在单个 MySQL 查询中获取多行，请使用 LIKE 运算符。让我们首先创建一个表：mysql> create table DemoTable1385    -> (    -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    -> Name varchar(20)    -> ); Query OK, 0 rows affected (0.90 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable1385(Name) values('Chris Brown'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable1385(Name) values('Adam Smith'); Query OK, 1 row affected (0.22 sec) mysql> insert into DemoTable1385(Name) values('Carol Taylor'); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable1385(Name) values('John ... 阅读更多

让我们首先创建一个表：mysql> create table DemoTable1384    -> (    -> StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY,    -> StudentName varchar(20),    -> StudentAge int    -> ); Query OK, 0 rows affected (0.63 sec)使用 insert 命令在表中插入一些记录。在这里，我们正在单个查询中插入多行：mysql> insert into DemoTable1384(StudentName, StudentAge) values('Chris Brown', 21), ('David Miller', 22), -> ('Carol Taylor', 19), ('Adam Smith', 23); Query OK, 4 rows affected (0.11 sec) Records: 4  Duplicates: 0  Warnings: 0使用 select 语句显示表中的所有记录：mysql> select * ... 阅读更多

为此，使用聚合函数 MAX()。 让我们首先创建一个表 -mysql> create table DemoTable1383    -> (    -> Id int,    -> PlayerScore int    -> ); Query OK, 0 rows affected (0.90 sec)使用 insert 命令在表中插入一些记录 -mysql> insert into DemoTable1383 values(200, 78); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable1383 values(200, 89); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable1383 values(200, 89); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable1383 values(200, 87); Query OK, 1 row affected (0.29 sec) mysql> insert into ... 阅读更多