From de2d8358dda08bfaf491d815df91d0c1ba33e7c9 Mon Sep 17 00:00:00 2001
From: Adam Chlipala <adam@chlipala.net>
Date: Tue, 13 Mar 2018 15:30:11 -0400
Subject: Handle empty SELECT clauses

---
 src/monoize.sml  | 27 +++++++++++++++------------
 src/postgres.sml | 11 +++++++++--
 2 files changed, 24 insertions(+), 14 deletions(-)

diff --git a/src/monoize.sml b/src/monoize.sml
index 60ff78ea..85a66e87 100644
--- a/src/monoize.sml
+++ b/src/monoize.sml
@@ -1792,18 +1792,21 @@ fun monoExp (env, st, fm) (all as (e, loc)) =
                                                                   NONE), loc),
                                                         str "")],
                                                       {disc = b, result = s}), loc),
-                                           strcatComma (map (fn (x, t) =>
-                                                                strcat [
-                                                                (L'.EField (gf "SelectExps", x), loc),
-                                                                str (" AS " ^ Settings.mangleSql x)
-                                                            ]) sexps
-                                                        @ map (fn (x, xts) =>
-                                                                  strcatComma
-                                                                      (map (fn (x', _) =>
-                                                                               str ("T_" ^ x
-										   ^ "."
-										   ^ Settings.mangleSql x'))
-                                                                           xts)) stables),
+                                           if List.null sexps andalso List.all (List.null o #2) stables then
+                                               str "0"
+                                           else
+                                               strcatComma (map (fn (x, t) =>
+                                                                    strcat [
+                                                                        (L'.EField (gf "SelectExps", x), loc),
+                                                                        str (" AS " ^ Settings.mangleSql x)
+                                                                ]) sexps
+                                                            @ map (fn (x, xts) =>
+                                                                      strcatComma
+                                                                          (map (fn (x', _) =>
+                                                                                   str ("T_" ^ x
+										        ^ "."
+										        ^ Settings.mangleSql x'))
+                                                                               xts)) stables),
                                            (L'.ECase (gf "From",
                                                       [((L'.PPrim (Prim.String (Prim.Normal, "")), loc),
                                                         str ""),
diff --git a/src/postgres.sml b/src/postgres.sml
index 404384d2..fac913f0 100644
--- a/src/postgres.sml
+++ b/src/postgres.sml
@@ -612,6 +612,13 @@ fun p_getcol {loc, wontLeakStrings, col = i, typ = t} =
         getter t
     end
 
+(* We turn 0-output queries into 1-output queries to satisfy SQL.
+ * This function adjusts our length expectations. *)
+fun bumpedLength ls =
+    case ls of
+        [] => 1
+      | _ => length ls
+
 fun queryCommon {loc, query, cols, doCols} =
     box [string "int n, i;",
          newline,
@@ -658,7 +665,7 @@ fun queryCommon {loc, query, cols, doCols} =
          newline,
 
          string "if (PQnfields(res) != ",
-         string (Int.toString (length cols)),
+         string (Int.toString (bumpedLength cols)),
          string ") {",
          newline,
          box [string "int nf = PQnfields(res);",
@@ -668,7 +675,7 @@ fun queryCommon {loc, query, cols, doCols} =
               string "uw_error(ctx, FATAL, \"",
               string (ErrorMsg.spanToString loc),
               string ": Query returned %d columns instead of ",
-              string (Int.toString (length cols)),
+              string (Int.toString (bumpedLength cols)),
               string ":\\n%s\\n%s\", nf, ",
               query,
               string ", PQerrorMessage(conn));",
-- 
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