sql: use precise capacity for row container in a few places

This commit audits all callers of `newContainerValuesNode` to specify
the precise capacity of the underlying row container since in all places
we know upfront how many rows the valuesNode will have. (Just happened to
notice it while working around one of those places.)

Epic: None

Release note: None

pkg/sql/explain_plan.go

@@ -162,7 +162,7 @@ func (e *explainPlanNode) startExec(params runParams) error {
 			rows = append(rows, fmt.Sprintf("   SQL command%s: %s", plural, recs[i].SQL))
 		}
 	}
-	v := params.p.newContainerValuesNode(colinfo.ExplainPlanColumns, 0)
+	v := params.p.newContainerValuesNode(colinfo.ExplainPlanColumns, len(rows))
 	datums := make([]tree.DString, len(rows))
 	for i, row := range rows {
 		datums[i] = tree.DString(row)

pkg/sql/show_cluster_setting.go

@@ -284,7 +284,7 @@ func planShowClusterSetting(
 				}
 			}
 
-			v := p.newContainerValuesNode(columns, 0)
+			v := p.newContainerValuesNode(columns, 1)
 			if _, err := v.rows.AddRow(ctx, tree.Datums{d}); err != nil {
 				v.rows.Close(ctx)
 				return nil, err

pkg/sql/show_histogram.go

@@ -75,7 +75,7 @@ func (p *planner) ShowHistogram(ctx context.Context, n *tree.ShowHistogram) (pla
 				return nil, err
 			}
 
-			v := p.newContainerValuesNode(showHistogramColumns, 0)
+			v := p.newContainerValuesNode(showHistogramColumns, len(histogram.Buckets))
 			resolver := descs.NewDistSQLTypeResolver(p.descCollection, p.InternalSQLTxn().KV())
 			if err := typedesc.EnsureTypeIsHydrated(ctx, histogram.ColumnType, &resolver); err != nil {
 				return nil, err

pkg/sql/show_stats.go

@@ -258,7 +258,11 @@ func (p *planner) ShowTableStats(ctx context.Context, n *tree.ShowTableStats) (p
 				}
 			}
 
-			v := p.newContainerValuesNode(columns, 0)
+			rowContainerCap := len(rows)
+			if n.UsingJSON {
+				rowContainerCap = 1
+			}
+			v := p.newContainerValuesNode(columns, rowContainerCap)
 			if n.UsingJSON {
 				result := make([]stats.JSONStatistic, 0, len(rows))
 				for _, r := range rows {

pkg/sql/show_zone_config.go

@@ -68,7 +68,7 @@ func (p *planner) ShowZoneConfig(ctx context.Context, n *tree.ShowZoneConfig) (p
 		name:    n.String(),
 		columns: showZoneConfigColumns,
 		constructor: func(ctx context.Context, p *planner) (planNode, error) {
-			v := p.newContainerValuesNode(showZoneConfigColumns, 0)
+			v := p.newContainerValuesNode(showZoneConfigColumns, 1)
 
 			// This signifies SHOW ALL.
 			// However, SHOW ALL should be handled by the delegate.