让我们首先创建一个表 -mysql> create table DemoTable778 ( ClientId varchar(100), ClientName varchar(100) ); Query OK, 0 rows affected (1.05 sec)使用 insert 命令在表中插入一些记录 -mysql> insert into DemoTable778 values('J-101', 'John'); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable778 values('A-102', 'Adam'); Query OK, 1 row affected (0.23 sec) mysql> insert into DemoTable778 values('C-103', 'Chris'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable778 values('D-104', 'David'); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable778 values('R-105', 'Robert'); Query OK, 1 row affected ... 阅读更多

让我们首先创建一个表 -mysql> create table DemoTable777 ( StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, StudentName varchar(100), StudentAge int ); Query OK, 0 rows affected (1.34 sec)使用 insert 命令在表中插入一些记录 -mysql> insert into DemoTable777(StudentName, StudentAge) values('Chris', 23); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable777(StudentName, StudentAge) values('Robert', 21); Query OK, 1 row affected (0.22 sec) mysql> insert into DemoTable777(StudentName, StudentAge) values('Mike', 19); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable777(StudentName, StudentAge) values('Bob', 22); Query OK, 1 row ... 阅读更多

假设您已将列值设置为唯一键，并尝试在表中插入重复值。这将导致 ERROR 1062 (23000)：Duplicate entry。让我们首先创建一个表 -mysql> create table DemoTable776 (    FirstValue int,    SecondValue int,    unique key(FirstValue, SecondValue) ); Query OK, 0 rows affected (0.74 sec)使用 insert 命令在表中插入一些记录。在插入重复值时，会出现与下面显示的相同的错误 -mysql> insert into DemoTable776 values(10, 20); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable776 values(10, 40); Query OK, 1 row affected (0.15 ... 阅读更多

让我们首先创建一个表 -mysql> create table DemoTable775 ( FirstName varchar(100) ); Query OK, 0 rows affected (0.78 sec)使用 insert 命令在表中插入一些记录 -mysql> insert into DemoTable775 values('Adam') ; Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable775 values('Carol'); Query OK, 1 row affected (0.22 sec) mysql> insert into DemoTable775 values('John'); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable775 values('Sam'); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable775 values('Adan'); Query OK, 1 row affected (0.15 sec)使用 select 语句显示表中的所有记录 -mysql> select ... 阅读更多

当前日期格式为“YYYY-mm-dd”。要更改当前日期格式，可以使用 date_format()。让我们首先显示当前日期 -mysql> select curdate();这将产生以下输出 -+------------+ | curdate() | +------------+ | 2019-08-08 | +------------+ 1 row in set (0.00 sec)以下是更改 curdate()（当前日期）格式的查询 -mysql> select date_format(curdate(), '%m/%d/%Y');这将产生以下输出 -+------------------------------------+ | date_format(curdate(), '%m/%d/%Y') | +------------------------------------+ | 08/08/2019                         | +------------------------------------+ 1 row in set (0.00 sec)让我们首先创建一个表 -mysql> create table DemoTable ... 阅读更多

为此，使用聚合函数 SUM()。在此方法中，将行值相乘。让我们首先创建一个表 -mysql> create table DemoTable(    ProductQuantity int,    ProductPrice int ); Query OK, 0 rows affected (0.48 sec)使用 insert 命令在表中插入一些记录 -mysql> insert into DemoTable values(10, 9); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable values(6, 20); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable values(7, 100); Query OK, 1 row affected (0.08 sec)使用 select 语句显示表中的所有记录 -mysql> select *from DemoTable;这将产生以下 ... 阅读更多

为此，使用 GROUP BY 子句以及聚合函数 SUM()。让我们首先创建一个表 -mysql> create table DemoTable(    Name varchar(100),    Score int ); Query OK, 0 rows affected (0.70 sec)使用 insert 命令在表中插入一些记录 -mysql> insert into DemoTable values('Adam', 50); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable values('Bob', 80); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable values('Adam', 70); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable values('Adam', 10); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable values('Carol', ... 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,    CustomerName varchar(100) ); Query OK, 0 rows affected (0.51 sec)使用 insert 命令在表中插入一些记录 -mysql> insert into DemoTable(CustomerName) values('Adam Smith'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable(CustomerName) values('Chris Brown'); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable(CustomerName) values('David Miller'); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable(CustomerName) values('Carol Taylot'); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable(CustomerName) values('Carol Taylor'); Query OK, 1 row affected ... 阅读更多

为此，您可以使用 CASE 语句。 让我们首先创建一个表 -mysql> create table DemoTable(    Id int,    Value int ); Query OK, 0 rows affected (0.51 sec)使用 insert 命令在表中插入一些记录 -mysql> insert into DemoTable values(10, 100); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable values(10, -110); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable values(10, 200); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable values(10, -678); Query OK, 1 row affected (0.17 sec)使用 select 语句显示表中的所有记录 -mysql> ... 阅读更多

让我们首先创建一个表 -mysql> create table DemoTable(    EmployeeId int NOT NULL AUTO_INCREMENT PRIMARY KEY,    EmployeeName varchar(100),    JoiningDate date ); Query OK, 0 rows affected (0.48 sec)使用 insert 命令在表中插入一些记录 -mysql> insert into DemoTable(EmployeeName, JoiningDate) values('Chris', '2019-01-21'); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable(EmployeeName, JoiningDate) values('Robert', '2016-12-01'); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable(EmployeeName, JoiningDate) values('Mike', '2015-03-12'); 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;这将产生以下输出 -+------------+--------------+-------------+ ... 阅读更多