找到 4219 篇文章 关于 MySQLi
![Krantik Chavan](https://tutorialspoint.com/assets/profiles/13545/profile/60_126883-1512724834.jpg)
183 次浏览
要选择两个值的差的绝对值大于某个特定数字的记录,以下为语法:select *from yourTableName where abs(yourColumnName1-yourColumnName2) >= yourCertainNumber;让我们先创建一个表:mysql> create table DemoTable ( Number1 int , Number2 int ); Query OK, 0 rows affected (0.59 sec)以下是使用 insert 命令在表中插入一些记录的查询:mysql> insert into DemoTable values(10, 20); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable values(100, 200); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable values(400, 300); Query OK, 1 ... 阅读更多
![George John](https://tutorialspoint.com/assets/profiles/13511/profile/60_58410-1512537824.png)
444 次浏览
要创建具有有限权限的 MySQL 用户,以下为语法:CREATE USER 'yourUserName'@'yourHostName' IDENTIFIED BY 'yourPassword';以下是为用户设置有限权限的语法:GRANT SELECT, INSERT, UPDATE, etc. REFERENCES ON yourDatabaseName.* TO 'yourUserName'@'yourHostName';让我们实现上述语法,以便创建具有有限权限的 MySQL 用户:mysql> CREATE USER 'David'@'localhost' IDENTIFIED BY 'david'; Query OK, 0 rows affected (0.20 sec) mysql> GRANT SELECT, INSERT, UPDATE, DELETE, ALTER, CREATE, REFERENCES ON test.* TO 'David'@'localhost'; Query OK, 0 rows affected (0.21 sec)让我们检查是否已创建名为“David”的用户。mysql> ... 阅读更多
![Krantik Chavan](https://tutorialspoint.com/assets/profiles/13545/profile/60_126883-1512724834.jpg)
369 次浏览
是的,您可以编写自己的 MySQL 函数在 MySQL 查询中使用。以下为语法:DELIMITER // CREATE FUNCTION yourFunctionName(可选参数)) RETURNS yourDataType DETERMINISTIC NO SQL BEGIN yourStatements1 . . . . N END // DELIMITER ;我们在上面使用了 CREATE FUNCTION 来创建一个自定义函数。让我们创建一个自定义 MySQL 函数在 MySQL 查询中使用:mysql> DELIMITER // mysql> CREATE FUNCTION get_First_Name(Name VARCHAR(255)) RETURNS VARCHAR(255) DETERMINISTIC NO SQL BEGIN RETURN LEFT(Name, LOCATE(' ', Name) - 1); END // Query OK, 0 rows affected (0.20 sec) mysql> DELIMITER ;现在调用 ... 阅读更多
![Chandu yadav](https://tutorialspoint.com/assets/profiles/22330/profile/60_142811-1519038104.jpg)
3K+ 次浏览
要将一列数据更新到另一列,可以使用 UPDATE 命令。让我们先创建一个表:mysql> create table DemoTable ( UserId int NOT NULL AUTO_INCREMENT PRIMARY KEY, UserFirstName varchar(20), ListOfName varchar(20) ); 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(UserFirstName, ListOfName) values('John', 'Larry'); Query OK, 1 row affected (0.29 sec) mysql> insert into DemoTable(UserFirstName, ListOfName) values('Carol', null); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable(UserFirstName, ListOfName) values('David', 'Sam'); Query OK, 1 row affected (0.22 sec) mysql> insert into DemoTable(UserFirstName, ListOfName) ... 阅读更多
![Krantik Chavan](https://tutorialspoint.com/assets/profiles/13545/profile/60_126883-1512724834.jpg)
85 次浏览
为了删除 MySQL 中表中的每一列,可以使用 DROP TABLE 命令。以下为语法:DROP TABLE yourTableName;让我们先创建一个表:mysql> create table DemoTable ( StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, StudentFirstName varchar(20), StudentLastName varchar(20), StudentAge int, StudentAddress varchar(200), StudentCountryName varchar(30), StudentDateOfBirth datetime ); Query OK, 0 rows affected (0.85 sec)让我们使用 DESC 命令检查表的描述:mysql> desc DemoTable;这将产生以下输出:+--------------------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key ... 阅读更多
![Arjun Thakur](https://tutorialspoint.com/assets/profiles/13574/profile/60_74441-1560315595.jpg)
2K+ 次浏览
要设置标志,可以将其类型设置为 tinyint(1) 类型。以下为语法:yourColumnName tinyint(1) DEFAULT 1;让我们先创建一个表:mysql> create table DemoTable ( ClientId int NOT NULL AUTO_INCREMENT PRIMARY KEY, ClientName varchar(20), isMarried tinyint(1) DEFAULT 1 ); Query OK, 0 rows affected (0.64 sec)使用 insert 命令在表中插入一些记录:mysql> INSERT INTO DemoTable(ClientName, isMarried) values('Larry', 0); Query OK, 1 row affected (0.16 sec) mysql> INSERT INTO DemoTable(ClientName) values('David'); Query OK, 1 row affected (0.12 sec) mysql> INSERT INTO DemoTable(ClientName, isMarried) values('Mike', 1); Query OK, 1 row affected (0.19 ... 阅读更多
![Krantik Chavan](https://tutorialspoint.com/assets/profiles/13545/profile/60_126883-1512724834.jpg)
2K+ 次浏览
您可以使用 ORDER BY SUBSTRING() 在 MySQL 中按字符串的特定部分排序。让我们先创建一个表:mysql> create table DemoTable (UserId varchar(200)); Query OK, 0 rows affected (0.68 sec)以下是使用 insert 命令在表中插入记录的查询:mysql> insert into DemoTable values('USER_1234'); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable values('USER_John'); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable values('USER_Sam'); Query OK, 1 row affected (0.22 sec) mysql> insert into DemoTable values('USER_Carol'); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable values('USER_Bob'); Query OK, ... 阅读更多
![Ankith Reddy](https://tutorialspoint.com/assets/profiles/22328/profile/60_142162-1519038074.jpg)
373 次浏览
您可以使用 AS 命令为 MySQL 结果中显示的表设置别名。以下为语法:SELECT TABLE_NAME AS anyAliasName FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = DATABASE();让我们实现上述语法:mysql> SELECT TABLE_NAME AS MY_TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = DATABASE();这将产生以下输出:+------------------------------------+ | MY_TABLE_NAME | +------------------------------------+ | a | | accumulateddemo | | add10minutedemo ... 阅读更多
![Krantik Chavan](https://tutorialspoint.com/assets/profiles/13545/profile/60_126883-1512724834.jpg)
465 次浏览
以下是针对正值或负值在 select 查询中使用 GROUP BY 的语法:select *from yourTableName group by -yourColumnName;让我们先创建一个表:mysql> create table DemoTable (Value int); Query OK, 0 rows affected (0.60 sec)以下是使用 insert 命令在表中插入一些记录的查询:mysql> insert into DemoTable values(-10); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable values(-20); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable values(20); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable values(10); Query OK, 1 row affected (0.13 sec) mysql> insert ... 阅读更多
![George John](https://tutorialspoint.com/assets/profiles/13511/profile/60_58410-1512537824.png)
550 次查看
让我们首先创建一个表。这里,我们有两个 varchar 类型的列:mysql> create table DemoTable ( UserId int NOT NULL AUTO_INCREMENT PRIMARY KEY, UserFirstName varchar(10), UserLastName varchar(20) , UserAge int ); Query OK, 0 rows affected (0.96 sec)让我们使用 DESC 命令检查表的描述:mysql> desc DemoTable;这将产生以下输出:+---------------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +---------------+-------------+------+-----+---------+----------------+ | UserId | int(11) | NO ... 阅读更多