要从多个 select 语句获取结果，可以使用 UNION ALL。以下是语法：select yourValue1 AS anyColumnName UNION ALL select yourValue2 AS yourColumnName . . . . N让我们实现上述语法，以便在不同的行中返回数字的枚举：mysql> select 100 AS Number    UNION ALL    select 1000 AS Number    UNION ALL    select 10000 AS Number    UNION ALL    select 100000 AS Number    UNION ALL    select 1000000 AS Number    UNION ALL    select 10000000 AS Number    UNION ALL    select 100000000 AS Number    UNION ALL    select 1000000000 AS Number;这将产生以下输出：-+------------+ | Number     | +------------+ | 100 | | 1000 | | 10000 | | 100000 | | 1000000 | | 10000000 | | 100000000 | | 1000000000 | +------------+ 8 rows in set (0.00 sec)

要选择最后两行，请使用 ORDER BY DESC LIMIT 2。让我们首先创建一个表：mysql> create table DemoTable763 (    Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    FirstName varchar(100) ); 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 DemoTable763(FirstName) values('John'); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable763(FirstName) values('Sam'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable763(FirstName) values('Carol'); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable763(FirstName) values('David'); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable763(FirstName) ... 阅读更多

为此，您可以使用带 OR 条件的 LIKE 运算符。让我们首先创建一个表：mysql> create table DemoTable762 (Title text); Query OK, 0 rows affected (0.54 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable762 values('Introduction to Java'); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable762 values('MySQL is a RDBMS'); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable762 values('Data Structure and Algorithm in Java'); Query OK, 1 row affected (0.21 sec) mysql> insert into DemoTable762 values('Data Structure and Algorithm in C and C++'); Query OK, 1 row affected (0.18 ... 阅读更多

字符串（列值）以一个字符开头，其余字符串包含数字。我们想要这些数字的总和：J230 A130s C13为此，请使用 SUBSTRING() 函数以及 SUM()。让我们首先创建一个表：mysql> create table DemoTable761 (Price varchar(100)); Query OK, 0 rows affected (0.62 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable761 values('J230'); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable761 values('A130'); Query OK, 1 row affected (0.70 sec) mysql> insert into DemoTable761 values('C13'); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable761 values('D456'); Query ... 阅读更多

让我们首先创建一个表：mysql> create table DemoTable760 (    ClientId int,    ClientId2 int ); Query OK, 0 rows affected (0.79 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable760 values(100, 200); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable760 values(100, 200); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable760 values(300, 400); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable760 values(300, 400); Query OK, 1 row affected (0.26 sec) mysql> insert into DemoTable760 values(100, 200); Query OK, 1 row affected (0.23 sec) mysql> insert ... 阅读更多

要设置 NULL 值，请将类型设置为 NULL，如下面的语法所示：yourColumnName dataType NULL;让我们首先创建一个表：mysql> create table DemoTable759 (    Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    FirstName varchar(100) NULL ); Query OK, 0 rows affected (0.72 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable759(FirstName) values('John'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable759(FirstName) values(NULL); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable759(FirstName) values('Carol'); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable759(FirstName) values(NULL); Query OK, 1 row ... 阅读更多

要设置默认值，请使用 DEFAULT 关键字。让我们首先创建一个表：mysql> create table DemoTable758 (    Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    FirstName varchar(100) ); Query OK, 0 rows affected (0.66 sec)以下是为列设置默认值的查询：mysql> alter table DemoTable758 add column Colors ENUM('RED', 'GREEN', 'BLUE', 'ORANGE', 'YELLOW') DEFAULT 'YELLOW'; Query OK, 0 rows affected (0.44 sec) Records: 0 Duplicates: 0 Warnings: 0让我们再次检查表的描述：mysql> desc DemoTable758;这将产生以下输出：-+-----------+----------------------------------------------+------+-----+---------+----------------+ | Field     | Type     ... 阅读更多

假设您在表中有一个 VARCHAR 列，其值为字符串，数字位于右侧。例如：John1023 Carol9871 David9098现在，假设您希望根据整个列中这些右侧的数字进行排序。为此，请使用 ORDER BY RIGHT。让我们首先创建一个表：mysql> create table DemoTable757 ( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, ClientId varchar(100) ); Query OK, 0 rows affected (0.53 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable757(ClientId) values('John1023'); Query OK, 1 row ... 阅读更多

让我们首先创建一个表：mysql> create table DemoTable756 (    Value1 int,    Value2 int,    Value3 int ); Query OK, 0 rows affected (0.62 sec)使用 insert 命令在表中插入一些记录：mysql> insert into DemoTable756 values(10, 20, 14); Query OK, 1 row affected (0.22 sec) mysql> insert into DemoTable756 values(20, 34, 17); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable756 values(200, 134, 789); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable756 values(139, 98, 99); Query OK, 1 row affected (0.17 sec)使用 select 语句显示表中的所有记录 ... 阅读更多

为此，在 HAVING 子句中使用别名。让我们首先创建一个表 -mysql> create table DemoTable755 (    Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    Score1 int,    Score2 int ); Query OK, 0 rows affected (0.62 sec)使用 insert 命令在表中插入一些记录 -mysql> insert into DemoTable755(Score1, Score2) values(30, 23); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable755(Score1, Score2) values(50, 60); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable755(Score1, Score2) values(89, 90); Query OK, 1 row affected (0.29 sec) mysql> insert into DemoTable755(Score1, Score2) values(99, 99); Query OK, 1 row ... 阅读更多