一对多联接，多个记录作为重复的列

Question

Using MS SQL Server. I have to build a view with columns from two entities that have a one-to-many relationship. The primary entity is Performance Reports. The table should have one performance report per row.

The related entity is Performance Report Logs. Each record includes one Problem and an unlimited number of Inputs. This structure was chosen in order to be able to link certain problems with certain inputs, rather than just having a list of all problems and all inputs in the Performance Report entity itself. Each Performance Report Log is linked to a Performance Report via lookup.

I would like the view to have the columns from the main Performance Report entity, followed by the columns from all related Performance Report Logs. So, if a Performance Report has three Logs, the columns from all three logs should be included in the same row, rather than three rows. They should also be in separate columns, not merged into one as in group_concat.

Thank you!

Answer 1

Is it truly "an unlimited number of Inputs"? If this is an overstatement and you might only have 10-20 inputs, you could use a SELECT statement for each Input column you wish to display. Ie,

select performance.field1, performance.field2,  
(select field from inputs where problem='x' and inputs.id=performance.pk) as X, 
(select field from inputs where problem='y' and inputs.id=performance.pk) as Y, 
etc...
        from Performance