使用 MySQL UPDATE 语句中的 if 语句设置条件来显示记录
mysqlmysqli database
首先我们创建一个表 −
mysql> create table DemoTable -> ( -> StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> StudentName varchar(20), -> StudentMarks int, -> Status varchar(20) -> ); Query OK, 0 rows affected (0.97 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable(StudentName,StudentMarks) values('Chris',79);
Query OK, 1 row affected (0.17 sec)
mysql> insert into DemoTable(StudentName,StudentMarks) values('David',59);
Query OK, 1 row affected (0.16 sec)
mysql> insert into DemoTable(StudentName,StudentMarks) values('Bob',60);
Query OK, 1 row affected (0.23 sec)
mysql> insert into DemoTable(StudentName,StudentMarks) values('Mike',45);
Query OK, 1 row affected (0.16 sec)
使用 select 语句显示表中的所有记录 −
mysql> select *from DemoTable;
这将产生以下输出 −
+-----------+-------------+--------------+--------+ | StudentId | StudentName | StudentMarks | Status | +-----------+-------------+--------------+--------+ | 1 | Chris | 79 | NULL | | 2 | David | 59 | NULL | | 3 | Bob | 60 | NULL | | 4 | Mike | 45 | NULL | +-----------+-------------+--------------+--------+ 4 rows in set (0.00 sec)
以下是在更新时设置条件的查询 −
mysql> update DemoTable -> set Status=if(StudentMarks > 60 ,'PASS','FAIL'); Query OK, 4 rows affected (0.40 sec) Rows matched: 4 Changed: 4 Warnings: 0
让我们再次检查表记录 −
mysql> select *from DemoTable;
这将产生以下输出 −
+-----------+-------------+--------------+--------+ | StudentId | StudentName | StudentMarks | Status | +-----------+-------------+--------------+--------+ | 1 | Chris | 79 | PASS | | 2 | David | 59 | FAIL | | 3 | Bob | 60 | FAIL | | 4 | Mike | 45 | FAIL | +-----------+-------------+--------------+--------+ 4 rows in set (0.00 sec)
