在 MySQL 中选择单行?
mysqlmysqli database
如果要根据主键选择单行，请使用 WHERE 子句。语法如下 −
SELECT * FROM yourTableName WHERE yourPrimaryKeyColumnName = someValue;
为了理解上述语法，让我们创建一个表。创建表的查询如下 −
mysql> create table selectWithPrimaryKey -> ( -> Id int NOT NULL AUTO_INCREMENT, -> Name varchar(20), -> Age int, -> Marks int, -> PRIMARY KEY(Id) -> ); Query OK, 0 rows affected (0.78 sec)
使用 insert 命令在表中插入一些记录。 查询语句如下 −
mysql> insert into selectWithPrimaryKey(Name,Age,Marks) values('Larry',24,98);
Query OK, 1 row affected (0.15 sec)
mysql> insert into selectWithPrimaryKey(Name,Age,Marks) values('John',23,89);
Query OK, 1 row affected (0.21 sec)
mysql> insert into selectWithPrimaryKey(Name,Age,Marks) values('Mike',21,85);
Query OK, 1 row affected (0.18 sec)
mysql> insert into selectWithPrimaryKey(Name,Age,Marks) values('Sam',26,56);
Query OK, 1 row affected (0.18 sec)
mysql> insert into selectWithPrimaryKey(Name,Age,Marks) values('Carol',21,59);
Query OK, 1 row affected (0.18 sec)
mysql> insert into selectWithPrimaryKey(Name,Age,Marks) values('Bob',20,91);
Query OK, 1 row affected (0.21 sec)
mysql> insert into selectWithPrimaryKey(Name,Age,Marks) values('David',28,93);
Query OK, 1 row affected (0.15 sec)
使用 select 语句显示表中的所有记录。查询如下 −
mysql> select *from selectWithPrimaryKey;
以下是输出 −
+----+-------+------+-------+ | Id | Name | Age | Marks | +----+-------+------+-------+ | 1 | Larry | 24 | 98 | | 2 | John | 23 | 89 | | 3 | Mike | 21 | 85 | | 4 | Sam | 26 | 56 | | 5 | Carol | 21 | 59 | | 6 | Bob | 20 | 91 | | 7 | David | 28 | 93 | +----+-------+------+-------+ 7 rows in set (0.00 sec)
以下是从表中选择单行的查询 −
mysql> select *from selectWithPrimaryKey where Id = 6;
这是输出 −
+----+------+------+-------+ | Id | Name | Age | Marks | +----+------+------+-------+ | 6 | Bob | 20 | 91 | +----+------+------+-------+ 1 row in set (0.00 sec)
