使用 IS NOT NULL 来显示非 NULL 记录。让我们首先创建一个表：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

让我们首先创建一个表：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 的 ISNULL() 函数。让我们首先创建一个表：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。让我们首先创建一个表：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：mysql> DELIMITER // mysql> CREATE PROCEDURE return_value() -> BEGIN -> SET @returnQuery= 'SELECT 98 INTO @value'; -> PREPARE stmt FROM @returnQuery; -> EXECUTE stmt; -> END -> // Query OK, 0 rows affected (0.20 sec) mysql> DELIMITER ; 使用 CALL 命令调用存储过程。mysql> call return_value(); Query OK, 1 row affected (0.07 sec) 使用 select 语句显示值：mysql> select @value;output 这将产生以下输出：+--------+ | @value | +--------+ | 98 | +--------+ 1 row in set (0.00 sec)

让我们首先创建一个表：mysql> create table DemoTable -> ( -> Name varchar(100), -> DueDate datetime -> ); Query OK, 0 rows affected (0.54 sec) 使用 insert 命令在表中插入一些记录。假设当前日期是“2019-07-03”：mysql> insert into DemoTable values('Chris', '2019-06-24'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable values('Chris', '2018-01-01'); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable values('Robert', '2019-07-03'); Query OK, 1 row affected (0.21 sec) mysql> insert into DemoTable values('Carol', '2019-08-03'); Query OK, 1 row affected (0.22 ... 阅读更多

让我们首先创建一个表：mysql> create table DemoTable -> ( -> value int -> ); Query OK, 0 rows affected (0.82 sec) 使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable values(10); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable values(100); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable values(20); Query OK, 1 row affected (0.28 sec) mysql> insert into DemoTable values(10); Query OK, 1 row affected (0.34 sec) mysql> insert into DemoTable values(30); Query OK, 1 row affected (0.24 sec) ... 阅读更多

要在 MySQL 存储过程中创建一个临时表，以下是语法：CREATE PROCEDURE yourProcedureName() BEGIN CREATE TEMPORARY TABLE yourTemporaryTableName SELECT yourValue; END让我们实现上述语法来创建一个临时表并在表中插入一些记录。以下是创建存储过程和临时表的查询：mysql> DELIMITER // mysql> CREATE PROCEDURE create_Temporary_Table() -> BEGIN -> CREATE TEMPORARY TABLE tmpDemoTable SELECT 500; -> END// Query OK, 0 rows affected (0.15 sec) 以下是向表中插入记录的查询：mysql> ... 阅读更多

让我们首先创建一个表：mysql> create table DemoTable -> ( -> EmployeeName varchar(100) -> ); Query OK, 0 rows affected (0.81 sec) 使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable values('Adam Smith'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable values('Carol Taylor'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable values('David Miller'); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable values('Chris Evan'); Query OK, 1 row affected (0.13 sec) 使用 select 语句显示表中的所有记录：mysql> select ... 阅读更多

要获取字符长度，可以使用 CHAR_LENGTH() 方法。让我们先创建一个表：
mysql> create table DemoTable
  > (
    > Name varchar(100)
    > );
Query OK, 0 rows affected (1.04 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 (0.13 sec)
mysql> insert into DemoTable values('Robert');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable values('Bob');
Query OK, 1 row affected (0.20 sec)
mysql> insert into DemoTable values('David');
Query OK, 1 row affected (0.15 sec)
显示表中的所有记录... 阅读更多