让我们首先创建一个表 −mysql> create table DemoTable1955 ( UserId int NOT NULL AUTO_INCREMENT , PRIMARY KEY(UserId) ); Query OK, 0 rows affected (0.00 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable1955 values(); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1955 values(); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1955 values(); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1955 values(); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1955 values(); Query OK, 1 row affected (0.00 sec)显示 ... 阅读更多

要获取星期几，请在 MySQL 中使用 DAYNAME() 函数。让我们首先创建一个表 −mysql> create table DemoTable1954 ( ShippingDate date ); Query OK, 0 rows affected (0.00 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable1954 values('2019-12-15'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1954 values('2018-04-11'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1954 values('2019-01-31'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1954 values('2016-10-01'); Query OK, 1 row affected (0.00 sec)使用 select 语句显示表中的所有记录 −mysql> select * ... 阅读更多

让我们首先创建一个表 −mysql> create table DemoTable1953 ( StudentName varchar(20) ); Query OK, 0 rows affected (0.00 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable1953 values('Chris'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1953 values(NULL); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1953 values('David'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1953 values(NULL); Query OK, 1 row affected (0.00 sec)使用 select 语句显示表中的所有记录 −mysql> select * from DemoTable1953;这将产生以下输出 −+-------------+ | ... 阅读更多

为此，请使用 CASE 语句。让我们首先创建一个表 −mysql> create table DemoTable1952 ( Marks int ); Query OK, 0 rows affected (0.00 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable1952 values(35); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1952 values(65); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1952 values(55); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1952 values(39); Query OK, 1 row affected (0.00 sec)使用 select 语句显示表中的所有记录 −mysql> select * from DemoTable1952;这将产生 ... 阅读更多

要将浮点值拆分为两列，第一列将包含小数点之前的数值。第二列将包含小数点之后的数值。为此，您可以使用 SUBSTRING_INDEX() 以及 CAST()。让我们首先创建一个表 −mysql> create table DemoTable1951 ( Value1 varchar(20) ); Query OK, 0 rows affected (0.00 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable1951 values('100.50'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1951 values('70.90'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1951 values('1000.55'); Query OK, 1 row affected ... 阅读更多

让我们创建一个表 −mysql> create table DemoTable1950 ( Amount float ); Query OK, 0 rows affected (0.00 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable1950 values(45.60); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1950 values(101.78); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1950 values(75.90); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1950 values(89.45); Query OK, 1 row affected (0.00 sec)使用 select 语句显示表中的所有记录 −mysql> select * from DemoTable1950;这将产生以下输出 −+--------+ | Amount ... 阅读更多

要为现有列设置 NOT NULL 属性，请使用 ALTER TABLE 命令。让我们首先创建一个表 −mysql> create table DemoTable1949 ( UserId int, UserName varchar(20) ); Query OK, 0 rows affected (0.00 sec)以下是为现有列设置 NOT NULL 属性的查询 −mysql> alter table DemoTable1949 modify UserName varchar(20) not null; Query OK, 0 rows affected (0.00 sec) Records: 0 Duplicates: 0 Warnings: 0让我们检查表的描述 −mysql> desc DemoTable1949;这将产生以下输出 −+----------+-------------+------+-----+---------+-------+ | Field | Type | Null | ... 阅读更多

要仅对字母数字字符串中的数字进行排序，请使用 ORDER BY RIGHT()。让我们首先创建一个表 −mysql> create table DemoTable1948 ( StudentCode varchar(20) ); Query OK, 0 rows affected (0.00 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable1948 values('121John_567'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1948 values('Adam_101'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1948 values('Bob_563'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1948 values('Sam_346'); Query OK, 1 row affected (0.00 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 DemoTable1947 ( Id int, Name varchar(20) ); Query OK, 0 rows affected (0.00 sec)使用 insert 命令在表中插入一些记录 −mysql> insert into DemoTable1947 values(101, 'Chris'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1947 values(102, 'David'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1947 values(103, 'Mike'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1947 values(104, 'Bob'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1947 values(105, 'Sam'); Query OK, 1 row affected (0.00 sec)显示 ... 阅读更多

Query OK, 1 ... 阅读更多