Question

I am building a reporting database and part of the requirements is creating multiple boolean columns to flatten 1:M relationships. Here’s an example:

Table 1 is Study Table and has a unique id.

Table 2 is Languages Table and has a 1:many relationship with Table 1.

Study Table
Id    Name
1     Study1
2     Study2
3     Study3

LanguageTable
StudyId    Language
1          English
1          French
1          Chinese
2          French
3          Chinese

I want to have a few columns in my report table such as Is In English or Is in European Language i.e

Study Language Report
StudyId      IsInEnglish        IsInEuropeanLanguage
1            true               true                   
2            false              true
3            false              false

How would I build a SQL query to generate this table given Table 1 and Table2?

Answer 1

   select s.StudyId,
          max(case when Language='English' then 1 else 0 end) IsInEnglish,
          max(case when Language in ('English','French') then 1 else 0 end) IsInEuropeanLanguage
     from study s
left join languages l on s.studyid = l.studyid
 group by s.studyid