CASE WHEN IFNULL
时间: 2024-02-10 10:32:01 浏览: 25
CASE WHEN和IFNULL是SQL中常用的条件判断函数。CASE WHEN函数用于在条件满足时返回一个结果,否则返回另一个结果。它可以在CASE和END之间有多个WHEN...THEN...ELSE语句。IFNULL函数用于判断一个值是否为NULL,如果是NULL则返回指定的默认值。例如,使用IFNULL函数可以将NULL值替换为0。[1][2][3]
相关问题
CASE WHEN IFNULL( t_temp.id, 0 ) = 0 THEN "" ELSE "selected" END AS "selected"
This is a SQL query that uses the CASE WHEN statement to check if the id value in the t_temp table is null or not. If the id value is null, the query will return an empty string. If the id value is not null, the query will return the string "selected". The IFNULL function is used to replace any null values with a zero value.
The query assigns the result of the CASE WHEN statement to the "selected" alias. This alias can be used to refer to the value returned by the query in other parts of the SQL statement.
CASE WHEN IFNULL( t_temp.id, 0 ) = 0 THEN "" ELSE "selected" END AS "selected"用中文解释
这段代码的意思是:如果t_temp.id为空,则返回空字符串,否则返回"selected"。其中,IFNULL函数用于判断t_temp.id是否为空,如果为空则返回0,否则返回t_temp.id的值。而CASE WHEN语句用于根据条件返回不同的值。最终结果为一个名为"selected"的字段,该字段的值为""或"selected"。