将MySQL null转换为0？
使用IFNULL或COALESCE()function以便将MySQLNULL转换为0。
语法如下
SELECT IFNULL(yourColumnName,0) AS anyAliasName FROM yourTableName; The second syntax is as follows: SELECT COALESCE(yourColumnName,0) AS anyAliasName FROM yourTableName;
让我们首先创建一个表。创建表的查询如下
mysql> create table convertNullToZeroDemo -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> Name varchar(20), -> Salary int -> );
使用insert命令在表中插入一些记录。
查询如下
mysql> insert into convertNullToZeroDemo(Name,Salary) values('John',NULL);
mysql> insert into convertNullToZeroDemo(Name,Salary) values('Carol',5610);
mysql> insert into convertNullToZeroDemo(Name,Salary) values('Bob',NULL);
mysql> insert into convertNullToZeroDemo(Name,Salary) values('David',NULL);使用select语句显示表中的所有记录。
查询如下
mysql> select *from convertNullToZeroDemo;
以下是输出
+----+-------+--------+ | Id | Name | Salary | +----+-------+--------+ | 1 | John | NULL | | 2 | Carol | 5610 | | 3 | Bob | NULL | | 4 | David | NULL | +----+-------+--------+ 4 rows in set (0.05 sec)
这是将MySQLNULL转换为0的第一个查询
mysql> select IFNULL(Salary,0) as `CONVERT_NULL _TO_0` from convertNullToZeroDemo;
以下是输出
+--------------------+ | CONVERT_NULL _TO_0 | +--------------------+ | 0 | | 5610 | | 0 | | 0 | +--------------------+ 4 rows in set (0.05 sec)
这是第二个将MySQLNULL转换为0的查询
mysql> select coalesce(Salary,0) as `CONVERT_NULL _TO_0` from convertNullToZeroDemo;
以下是输出
+--------------------+ | CONVERT_NULL _TO_0 | +--------------------+ | 0 | | 5610 | | 0 | | 0 | +--------------------+ 4 rows in set (0.00 sec)