为了更快的查询，使用 MySQL IN()，因为它在内部使用索引。让我们先创建一个表 - mysql> create table DemoTable1618     -> (     -> ClientId int NOT NULL AUTO_INCREMENT PRIMARY KEY,     -> ClientName varchar(20),     -> ClientEmailId varchar(30)     -> ); Query OK, 0 rows affected (1.53 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable1618(ClientName, ClientEmailId) values('Chris Brown', '[email protected]'); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable1618(ClientName, ClientEmailId) values('David Miller', '[email protected]'); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable1618(ClientName, ClientEmailId) values('John Doe', ... 阅读更多

让我们先创建一个表 - mysql> create table DemoTable1368     -> (     -> ClientId int,     -> ClientName varchar(20)     -> ); Query OK, 0 rows affected (0.58 sec)使用 insert 命令在表中插入一些记录 - mysql> insert into DemoTable1368 values(101, 'Adam'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable1368 values(102, 'Bob'); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable1368 values(103, 'John'); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable1368 values(104, 'Sam'); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable1368 values(105, ... 阅读更多

要显示任何行和列，请使用 SELECT NULL 和 FALSE，如下面的语法所示 - select null from yourTableName where false;让我们先创建一个表 - mysql> create table DemoTable1367     -> (     -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,     -> FirstName varchar(20)     -> ); Query OK, 0 rows affected (0.55 sec)使用 insert 命令在表中插入一些记录 - mysql> insert into DemoTable1367(FirstName) values('Chris'); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable1367(FirstName) values('David'); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable1367(FirstName) values('Bob'); ... 阅读更多

为此，请使用 SUBSTR()，如下面的语法所示 - select * from yourTableName where substr(yourColumnName, 2, 1 ) = ' ';让我们先创建一个表 - mysql> create table DemoTable1365     -> (     -> Value varchar(20)     -> ); Query OK, 0 rows affected (0.66 sec)使用 insert 命令在表中插入一些记录 - mysql> insert into DemoTable1365 values('9756757474'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable1365 values('3 45322333'); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable1365 values('8974646363'); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable1365 values('9 ... 阅读更多

让我们先创建一个表。在这里，我们将日期设置为 VARCHAR - mysql> create table DemoTable1364     -> (     -> ShippingDate varchar(100)     -> ); Query OK, 0 rows affected (0.87 sec)使用 insert 命令在表中插入一些记录 - mysql> insert into DemoTable1364 values('01-09-2019 12:34:55'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable1364 values('01-07-2018 17:10:00'); Query OK, 1 row affected (0.37 sec) mysql> insert into DemoTable1364 values('24-09-2019 10:31:22'); Query OK, 1 row affected (0.24 sec) mysql> insert into DemoTable1364 values('20-09-2018 13:00:00'); Query OK, 1 row affected (0.13 sec)显示所有记录 ... 阅读更多

让我们先创建一个表 - mysql> create table DemoTable1363     -> (     -> StudentId varchar(20)     -> ); Query OK, 0 rows affected (0.57 sec)使用 insert 命令在表中插入一些记录 - mysql> insert into DemoTable1363 values('901'); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable1363 values('702'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable1363 values('901_John_Doe'); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable1363 values('1001_Carol_Taylor'); Query OK, 1 row affected (0.26 sec)使用 select 语句显示表中的所有记录 - mysql> select * from DemoTable1363;这将 ... 阅读更多

为此，语法如下 - revoke show databases on *.* from 'yourUserName'@'yourHostName';让我们显示所有用户名及其主机名 - mysql> select user, host from MySQL.user;这将产生以下输出 - +------------------+-----------+ | user             | host      | +------------------+-----------+ | Bob              | %         | | Charlie          | %         | | Robert           | %         | | User2            | %   ... 阅读更多

在存储过程中使用 MySQL DECLARE 定义变量 - DECLARE anyVariableName int DEFAULT anyValue;让我们实现上述语法以在存储过程中创建变量 - mysql> DELIMITER // mysql> CREATE PROCEDURE variable_Demo()     -> BEGIN     -> DECLARE lastInsertedId int DEFAULT -1;     -> select lastInsertedId;     -> set @providedLastId=10001;     -> select @providedLastId;     -> END     -> // Query OK, 0 rows affected (0.32 sec) mysql> DELIMITER ;现在可以使用 CALL 命令调用上述存储过程 - mysql> call variable_Demo();这将产生以下输出 - +----------------+ | lastInsertedId | ... 阅读更多

让我们先创建一个表 - mysql> create table DemoTable1362     -> (     -> ClientId int NOT NULL AUTO_INCREMENT PRIMARY KEY,     -> ClientName varchar(40)     -> ); 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 DemoTable1362(ClientName) values('Chris'); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable1362(ClientName) values(' '); Query OK, 1 row affected (0.08 sec) mysql> insert into DemoTable1362(ClientName) values('Bob'); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable1362(ClientName) values(' '); Query OK, 1 row affected (0.12 sec) mysql> insert ... 阅读更多

要查找两个特定的列名，可以使用information_schema.columns。这里，我使用Id代替columnA，使用Name代替columnB −mysql> select table_name as TableNameFromWebDatabase    -> from information_schema.columns    -> where column_name IN ('Id', 'Name')    -> group by table_name    -> having count(*) = 3;这将产生以下输出。以下是包含Id和Name列的表：−+--------------------------+ | TableNameFromWebDatabase | +--------------------------+ | student                  | | distinctdemo             | | secondtable              | | groupconcatenatedemo ... 阅读更多