opt: improve the partial index label in EXPLAIN

This commit moves the "partial index" mention next to the name of the
index.

Release note: None

pkg/sql/opt/exec/execbuilder/testdata/partial_index

@@ -286,9 +286,8 @@ InitPut /Table/53/4/"foo"/22/0 -> /BYTES/
 query TTT
 EXPLAIN SELECT b FROM t WHERE b > 10
 ----
-·     distribution   local
-·     vectorized     true
-scan  ·              ·
-·     table          t@b_partial
-·     spans          FULL SCAN
-·     partial index  ·
+·     distribution  local
+·     vectorized    true
+scan  ·             ·
+·     table         t@b_partial (partial index)
+·     spans         FULL SCAN

pkg/sql/walk.go

@@ -164,7 +164,7 @@ func (v *planVisitor) visitInternal(plan planNode, name string) {
 
 	case *scanNode:
 		if v.observer.attr != nil {
-			v.observer.attr(name, "table", fmt.Sprintf("%s@%s", n.desc.Name, n.index.Name))
+			v.observer.attr(name, "table", formatTable(n.desc, n.index))
 			if n.noIndexJoin {
 				v.observer.attr(name, "hint", "no index join")
 			}
@@ -183,9 +183,6 @@ func (v *planVisitor) visitInternal(plan planNode, name string) {
 			if n.parallelize {
 				v.observer.attr(name, "parallel", "")
 			}
-			if n.index.IsPartial() {
-				v.observer.attr(name, "partial index", "")
-			}
 			if n.hardLimit > 0 {
 				v.observer.attr(name, "limit", fmt.Sprintf("%d", n.hardLimit))
 			}
@@ -354,30 +351,20 @@ func (v *planVisitor) visitInternal(plan planNode, name string) {
 	case *interleavedJoinNode:
 		if v.observer.attr != nil {
 			v.observer.attr(name, "type", joinTypeStr(n.joinType))
-			v.observer.attr(name, "left table", fmt.Sprintf("%s@%s", n.left.desc.Name, n.left.index.Name))
+			v.observer.attr(name, "left table", formatTable(n.left.desc, n.left.index))
 		}
 		if v.observer.spans != nil {
 			v.observer.spans(name, "left spans", n.left.index, n.left.spans, n.left.hardLimit != 0)
 		}
-		if v.observer.attr != nil {
-			if n.left.index.IsPartial() {
-				v.observer.attr(name, "left partial index", "")
-			}
-		}
 		if v.observer.expr != nil {
 			v.expr(name, "left filter", -1, n.leftFilter)
 		}
 		if v.observer.attr != nil {
-			v.observer.attr(name, "right table", fmt.Sprintf("%s@%s", n.right.desc.Name, n.right.index.Name))
+			v.observer.attr(name, "right table", formatTable(n.right.desc, n.right.index))
 		}
 		if v.observer.spans != nil {
 			v.observer.spans(name, "right spans", n.right.index, n.right.spans, n.right.hardLimit != 0)
 		}
-		if v.observer.attr != nil {
-			if n.right.index.IsPartial() {
-				v.observer.attr(name, "right partial index", "")
-			}
-		}
 		if v.observer.expr != nil {
 			v.expr(name, "right filter", -1, n.rightFilter)
 			v.expr(name, "pred", -1, n.onCond)
@@ -844,6 +831,16 @@ func (v *planVisitor) metadataTuples(nodeName string, tuples [][]tree.TypedExpr)
 	}
 }
 
+// formatTable returns a string of the form "<table_name>@<index_name>", or
+// "<table_name>@<index_name> (partial index)" if the index is partial.
+func formatTable(desc *sqlbase.ImmutableTableDescriptor, index *sqlbase.IndexDescriptor) string {
+	partial := ""
+	if index.IsPartial() {
+		partial = " (partial index)"
+	}
+	return fmt.Sprintf("%s@%s%s", desc.Name, index.Name, partial)
+}
+
 // formatValuesSize returns a string of the form "5 columns, 1 row".
 func formatValuesSize(numRows, numCols int) string {
 	return fmt.Sprintf(