Add 'rows affected' output when using sql engine

NEWS.md

@@ -1,3 +1,7 @@
+- The `sql` engine now produces an output for update-like SQL queries, indicating the number of rows affected (as returned by DBI::dbExecute). So far, `knitr` produces a nicely formatted output for queries returning a result set (typically SELECT...), but gives no feedback at all for queries making changes to the DB (e.g. INSERT|UPDATE|DELETE|CREATE|DROP; see not exported function knitr:::is_sql_update_query). For such queries, `knitr` now shows the number of affected rows. You can also set the chunk option `output.var` to assign the number of affected rows to a variable.
+
+
+
 # CHANGES IN knitr VERSION 1.35
 
 ## BUG FIXES

R/engine.R

@@ -555,8 +555,8 @@ eng_sql = function(options) {
 
   data = tryCatch({
     if (is_sql_update_query(query)) {
-      DBI::dbExecute(conn, query)
-      NULL
+      data = DBI::dbExecute(conn, query)
+      data
     } else if (is.null(varname) && max.print > 0) {
       # execute query -- when we are printing with an enforced max.print we
       # use dbFetch so as to only pull down the required number of records
@@ -633,6 +633,11 @@ eng_sql = function(options) {
 
     } else print(display_data) # fallback to standard print
   })
+  if (is.numeric(data) && length(data) == 1 && is.null(varname)) {
+    options$results = 'asis'
+    # format = "fg" instead of "d". Row counts on DB may be greater than integer max value
+    output = paste0("Number of affected rows: ", formatC(data, format = "fg", big.mark = ','))
+  }
   if (options$results == 'hide') output = NULL
 
   # assign varname if requested