server, ui: handle null plan gist in getStatementDetailsPerPlanHash

This commit adds a new function that handles null plan gists in
`getStatementDetailsPerPlanHash`. The commit also adds some logic
to hide null plan gists in the Statement Details page.

Fixes #82095.

For more details, see #82095 (comment).

Release note: None

pkg/server/combined_statement_stats.go

@@ -729,8 +729,11 @@ func getStatementDetailsPerPlanHash(
 		if planHash, err = sqlstatsutil.DatumToUint64(row[0]); err != nil {
 			return nil, serverError(ctx, err)
 		}
-		planGist := string(tree.MustBeDString(row[1]))
-		explainPlan := getExplainPlanFromGist(ctx, ie, planGist)
+		planGist := string(tree.MustBeDStringOrDNull(row[1]))
+		var explainPlan string
+		if planGist != "" {
+			explainPlan = getExplainPlanFromGist(ctx, ie, planGist)
+		}
 
 		var metadata roachpb.CollectedStatementStatistics
 		var aggregatedMetadata roachpb.AggregatedStatementMetadata

pkg/sql/sem/tree/datum.go

@@ -24,7 +24,7 @@ import (
 	"unicode/utf8"
 	"unsafe"
 
-	"github.com/cockroachdb/apd/v3"
+	"github.com/cockroachdb/apd"
 	"github.com/cockroachdb/cockroach/pkg/geo"
 	"github.com/cockroachdb/cockroach/pkg/sql/lex"
 	"github.com/cockroachdb/cockroach/pkg/sql/lexbase"
@@ -1220,6 +1220,16 @@ func MustBeDString(e Expr) DString {
 	return i
 }
 
+// MustBeDStringOrDNull attempts to retrieve a DString or DNull from an Expr, panicking if the
+// assertion fails.
+func MustBeDStringOrDNull(e Expr) DString {
+	i, ok := AsDString(e)
+	if !ok && e != DNull {
+		panic(errors.AssertionFailedf("expected *DString or DNull, found %T", e))
+	}
+	return i
+}
+
 // ResolvedType implements the TypedExpr interface.
 func (*DString) ResolvedType() *types.T {
 	return types.String

pkg/ui/workspaces/cluster-ui/src/statementDetails/planDetails/planDetails.tsx

@@ -57,6 +57,7 @@ function renderExplainPlan(
   plan: PlanHashStats,
   backToPlanTable: () => void,
 ): React.ReactElement {
+  let explainPlan = plan.explain_plan === "" ? "unavailable" : plan.explain_plan;
   return (
     <div>
       <Helmet title="Plan Details" />
@@ -70,7 +71,7 @@ function renderExplainPlan(
       >
         All Plans
       </Button>
-      <SqlBox value={plan.explain_plan} size={SqlBoxSize.large} />
+      <SqlBox value={explainPlan} size={SqlBoxSize.large} />;
     </div>
   );
 }