vitessio/vitess · error

unsupported subquery: %v

Error message

unsupported subquery: %v

What it means

Subqueries anywhere in a select-list expression are unsupported in vreplication table plans. The sqlparser.Walk rejects *sqlparser.Subquery nodes because the materialization logic cannot evaluate a nested query per row.

Source

Thrown at go/vt/vttablet/tabletmanager/vreplication/table_plan_builder.go:528

				return nil, fmt.Errorf("unsupported qualifier for column: %v", sqlparser.String(innerCol))
			}
			cexpr.operation = opSum
			cexpr.expr = innerCol
			tpb.addCol(innerCol.Name)
			cexpr.references[innerCol.Name.String()] = true
			return cexpr, nil
		}
	}
	err := sqlparser.Walk(func(node sqlparser.SQLNode) (kontinue bool, err error) {
		switch node := node.(type) {
		case *sqlparser.ColName:
			if !node.Qualifier.IsEmpty() {
				return false, fmt.Errorf("unsupported qualifier for column: %v", sqlparser.String(node))
			}
			tpb.addCol(node.Name)
			cexpr.references[node.Name.String()] = true
		case *sqlparser.Subquery:
			return false, fmt.Errorf("unsupported subquery: %v", sqlparser.String(node))
		case sqlparser.AggrFunc:
			return false, fmt.Errorf("unsupported aggregation function: %v", sqlparser.String(node))
		}
		return true, nil
	}, aliased.Expr)
	if err != nil {
		return nil, err
	}
	cexpr.expr = aliased.Expr
	return cexpr, nil
}

// addCol adds the specified column to the send query
// if it's not already present.
func (tpb *tablePlanBuilder) addCol(ident sqlparser.IdentifierCI) {
	tpb.sendSelect.AddSelectExpr(&sqlparser.AliasedExpr{
		Expr: &sqlparser.ColName{Name: ident},
	})

View on GitHub (pinned to 01a25a7d17)

Solutions

1. Remove the subquery from the SELECT list.
2. Precompute the subquery result into a column (e.g. via a trigger or application logic) and select that column.
3. Run the subquery separately against VTGate instead of embedding it in the workflow query.

Example fix

// before
select id, (select max(v) from t2) as maxv from t
// after
select id, maxv from t  -- maxv maintained as a stored column

// Reject subqueries in the workflow SELECT before submitting
func noSubqueries(sel *sqlparser.Select) bool {
    found := false
    sqlparser.Walk(func(n sqlparser.SQLNode) (bool, error) {
        if _, ok := n.(*sqlparser.Subquery); ok { found = true; return false, nil }
        return true, nil
    }, sel)
    return !found
}

func isSubquery(n sqlparser.SQLNode) bool { _, ok := n.(*sqlparser.Subquery); return ok }

When it happens

Trigger: Materialize/vreplication SELECT containing a subquery, e.g. SELECT (SELECT max(x) FROM t2) AS m FROM t; the walk over aliased.Expr encounters the Subquery node.

Common situations: Porting complex reporting SQL into a materialization workflow; generated queries that embed lookups as scalar subqueries.

Related errors

• only count(*) is supported: %v
• unsupported multiple columns in sum clause: %v
• unsupported non-column name in sum clause: %v
• unsupported aggregation function: %v
• unsupported non-column name or alias in group by clause: %v

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/b523e9ee3f0ba74a. Report an issue: GitHub.