R Shiny应用程序中的SQL查询语法-CAST

Question

This is a follow up to this question: Working with reactiveValues and ggplot in shiny . I am making a shiny app that queries an SQL database. In my working example for the question, I managed to avoid changing the format of reactive data within shiny by using CAST to automatically import data with a specific format:

Query without cast

b <- reactive({ paste("select Wafer, Batch, MeasurementA, MeasurementB from dd where ID=",e()," Order by  ID asc ;", sep="") })

Query with cast to automatically change column format

b <- reactive({ paste("select cast(Wafer as varchar) as Wafer, cast(Batch as varchar) as Batch, MeasurementA, MeasurementB from dd where ID=",e()," Order by  ID asc ;", sep="") })

This worked fine in the working example I used for my question. However, when I came to apply this to my real app I get a syntax error:

b <- reactive({ paste("select cast(e.erf_num as varchar) as ERF, cast(w.wafer_id as varchar) as Wafer, d.name,d.row,d.col,d.width,d.length,t.test_date, 

                        t.von_fwd,t.vth_fwd,t.sts_fwd,t.on_off_fwd,t.curr_on_fwd,t.curr_off_fwd,t.rds_on_fwd, t.rds_on_fwd,
                        t.von_rev,t.vth_rev,t.sts_rev,t.on_off_rev,t.curr_on_rev,t.curr_off_rev,t.rds_on_rev, t.rds_on_rev, t.delta_vth, t.id

                        from transfer_data_temp AS t
                        inner join wafer AS w ON t.wafer_id=w.id
                        inner join device AS d ON t.device_id=d.id
                        inner join erf AS e on t.wafer_id=e.wafer_id

                        where
                        t.wafer_id=",e()," Order by  d.name asc , t.test_date;", sep="") })


Unhandled error in observer: could not run statement: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'varchar), cast(wafer.wafer_id as varchar), d.name,d.row,d.col,d.width,d.length,t' at line 1 

I know the query works without the CAST because ive used it successfully before. So I draw attention to this part of the query:

  b <- reactive({ paste("select cast(e.erf_num as varchar) as ERF, cast(w.wafer_id as varchar) as Wafer, 

Any ideas why this works in the former but not the latter? I can post all my code to give a full working example if it helps (avoided ATM because its a tad long). Thanks. Pete

Answer 1

ah ok, for some reason if I change AS varchar to AS character it works. Dont no why. I should have played around a bit more before asking the question!