postgresql - SQL Statement If statement inside a SELECT statement

Question

Is there a way that I can use if statement in a select statement?

I cannot use Case statement in this one. Actually I am using iReport and I have a parameter. What I want to do is if a user does not enter a certain parameter it will select all the instances.

For example a table of person referencing to gender table, a with a parameter on where clause, query would go like:

SELECT * FROM persontable WHERE gender_id = $P{genderName}:numeric

If the parameter $P{genderName} is null or blank then it will select all. I tried this query:

SELECT * FROM persontable WHERE gender_id IN (SELECT CASE WHEN $P{genderName} 
 IS NULL THEB (SELECT id from genderTable 
 WHERE id = $P{genderName}:numeric) ELSE $P{genderName}::numeric END)

But it will return an error "More that one row is returned....." I think it is because of the CASE statement. How do I this?

Answer 1

尝试这个：

SELECT * FROM persontable 
WHERE gender_id = $P{genderName} OR $P{genderName} IS NULL 

Answer 2

这可以使用辅助参数轻松实现。

在您的报告中定义一个新参数，将其命名为aux_gendername.

在定义参数时，调整其Default Value Expression。

($P{gendername}.equals("") || $P{gendername}==NULL? " " : " and gender_id = '"+$P{gendername}+"'")

然后在您的主查询中，使用辅助参数而不是实际参数 ($P{gendername})。

SELECT * FROM persontable WHERE 1=1 $P!{aux_gendername}

如果 $P{gendername} 包含任何值，并且条件将动态附加到查询中，否则整个结果集将显示在报告中而无需任何过滤。

注意：使用! 在辅助参数中是强制性的。