opt: add scan constant columns to ordering if they are in the output

pkg/sql/opt/ordering/scan.go

@@ -130,14 +130,20 @@ func scanBuildProvided(expr memo.RelExpr, required *props.OrderingChoice) opt.Or
 	// We generate the longest ordering that this scan can provide, then we trim
 	// it. This is the longest prefix of index columns that are output by the scan
 	// (ignoring constant columns, in the case of constrained scans).
-	// We start the for loop at the exact prefix since all columns in the exact
-	// prefix are constant and can be ignored.
+	outCols := expr.Relational().OutputCols
 	constCols := fds.ComputeClosure(opt.ColSet{})
 	numCols := index.KeyColumnCount()
 	provided := make(opt.Ordering, 0, numCols)
-	for i := scan.ExactPrefix; i < numCols; i++ {
+	for i := 0; i < numCols; i++ {
 		indexCol := index.Column(i)
 		colID := scan.Table.ColumnID(indexCol.Ordinal())
+		if i < scan.ExactPrefix && !outCols.Contains(colID) {
+			// All columns in the exact prefix are constant and can be ignored as long
+			// as they are not in the output of the scan. If an exact-prefix column is
+			// in the output, it may still be constant, but can only be ignored if the
+			// FDs "know" it is constant. This latter case is handled below as normal.
+			continue
+		}
 		if constCols.Contains(colID) {
 			// Column constrained to a constant, ignore.
 			continue

pkg/sql/opt/xform/testdata/physprops/ordering

@@ -2899,3 +2899,35 @@ project
                 ├── t0_85393.rowid:10 [as=t0_85393.rowid:2, outer=(10)]
                 ├── t1_85393.c0:13 [as=t1_85393.c0:5, outer=(13)]
                 └── t1_85393.rowid:14 [as=t1_85393.rowid:6, outer=(14)]
+
+# Regression test for #83793 - include scan columns that are constrained to be
+# constant in the provided ordering when they are in the output of the scan.
+exec-ddl
+CREATE TABLE t83793 (
+  a INT,
+  b STRING AS (a::STRING) STORED,
+  c STRING AS (a::STRING) VIRTUAL,
+  UNIQUE (b, a)
+);
+----
+
+opt format=hide-all
+SELECT NULL FROM t83793
+WHERE NOT (c NOT SIMILAR TO '')
+GROUP BY b HAVING bool_and(NULL);
+----
+project
+ ├── select
+ │    ├── group-by (streaming)
+ │    │    ├── project
+ │    │    │    ├── scan t83793@t83793_b_a_key
+ │    │    │    │    └── constraint: /2/1: [/'' - /'']
+ │    │    │    └── projections
+ │    │    │         └── NULL
+ │    │    └── aggregations
+ │    │         └── bool-and
+ │    │              └── column7
+ │    └── filters
+ │         └── bool_and
+ └── projections
+      └── NULL