Add support for UPDATE ... RETURNING

Author: fulghum

sql/analyzer/fix_exec_indexes.go

@@ -514,6 +514,10 @@ func (s *idxScope) visitSelf(n sql.Node) error {
 			newCheck.Expr = newE
 			s.checks = append(s.checks, &newCheck)
 		}
+		for _, r := range n.Returning {
+			newE := fixExprToScope(r, srcScope)
+			s.expressions = append(s.expressions, newE)
+		}
 	case *plan.LoadData:
 		scope := &idxScope{}
 		scope.addSchema(n.DestSch)
@@ -556,6 +560,10 @@ func (s *idxScope) finalizeSelf(n sql.Node) (sql.Node, error) {
 		nn.Returning = s.expressions[len(n.OnDupExprs):]
 		return nn.WithChecks(s.checks), nil
 	default:
+		if nn, ok := n.(*plan.Update); ok {
+			nn.Returning = s.expressions
+		}
+
 		s.ids = columnIdsForNode(n)
 
 		s.addSchema(n.Schema())

sql/plan/update.go

@@ -21,6 +21,7 @@ import (
 
 	"github.com/dolthub/go-mysql-server/sql"
 	"github.com/dolthub/go-mysql-server/sql/expression"
+	"github.com/dolthub/go-mysql-server/sql/transform"
 )
 
 var ErrUpdateNotSupported = errors.NewKind("table doesn't support UPDATE")
@@ -35,6 +36,10 @@ type Update struct {
 	IsJoin       bool
 	HasSingleRel bool
 	IsProcNested bool
+
+	// Returning is a list of expressions to return after the update operation. This feature is not
+	// supported in MySQL's syntax, but is exposed through PostgreSQL's syntax.
+	Returning []sql.Expression
 }
 
 var _ sql.Node = (*Update)(nil)
@@ -112,6 +117,24 @@ func GetDatabase(node sql.Node) sql.Database {
 	return nil
 }
 
+// Schema implements the sql.Node interface.
+func (u *Update) Schema() sql.Schema {
+	// Postgres allows the returned values of the update statement to be controlled, so if returning
+	// expressions were specified, then we return a different schema.
+	if u.Returning != nil {
+		// We know that returning exprs are resolved here, because you can't call Schema()
+		// safely until Resolved() is true.
+		returningSchema := sql.Schema{}
+		for _, expr := range u.Returning {
+			returningSchema = append(returningSchema, transform.ExpressionToColumn(expr, ""))
+		}
+
+		return returningSchema
+	}
+
+	return u.Child.Schema()
+}
+
 func (u *Update) Checks() sql.CheckConstraints {
 	return u.checks
 }
@@ -140,24 +163,32 @@ func (u *Update) Database() string {
 }
 
 func (u *Update) Expressions() []sql.Expression {
-	return u.checks.ToExpressions()
+	exprs := append([]sql.Expression{}, u.checks.ToExpressions()...)
+	exprs = append(exprs, u.Returning...)
+	return exprs
 }
 
 func (u *Update) Resolved() bool {
-	return u.Child.Resolved() && expression.ExpressionsResolved(u.checks.ToExpressions()...)
+	return u.Child.Resolved() &&
+		expression.ExpressionsResolved(u.checks.ToExpressions()...) &&
+		expression.ExpressionsResolved(u.Returning...)
+
 }
 
 func (u Update) WithExpressions(newExprs ...sql.Expression) (sql.Node, error) {
-	if len(newExprs) != len(u.checks) {
-		return nil, sql.ErrInvalidChildrenNumber.New(u, len(newExprs), len(u.checks))
+	expectedLength := len(u.checks) + len(u.Returning)
+	if len(newExprs) != expectedLength {
+		return nil, sql.ErrInvalidChildrenNumber.New(u, len(newExprs), expectedLength)
 	}
 
 	var err error
-	u.checks, err = u.checks.FromExpressions(newExprs)
+	u.checks, err = u.checks.FromExpressions(newExprs[:len(u.checks)])
 	if err != nil {
 		return nil, err
 	}
 
+	u.Returning = newExprs[len(u.checks):]
+
 	return &u, nil
 }
 

sql/planbuilder/dml.go

@@ -581,6 +581,15 @@ func (b *Builder) buildUpdate(inScope *scope, u *ast.Update) (outScope *scope) {
 			return true
 		})
 	}
+
+	if len(u.Returning) > 0 {
+		returningExprs := make([]sql.Expression, len(u.Returning))
+		for i, selectExpr := range u.Returning {
+			returningExprs[i] = b.selectExprToExpression(outScope, selectExpr)
+		}
+		update.Returning = returningExprs
+	}
+
 	outScope.node = update.WithChecks(checks)
 	return
 }

sql/rowexec/dml.go

@@ -168,7 +168,7 @@ func (b *BaseBuilder) buildUpdate(ctx *sql.Context, n *plan.Update, row sql.Row)
 		return nil, err
 	}
 
-	return newUpdateIter(iter, updatable.Schema(), updater, n.Checks(), n.Ignore), nil
+	return newUpdateIter(iter, updatable.Schema(), updater, n.Checks(), n.Ignore, n.Returning, n.Schema()), nil
 }
 
 func (b *BaseBuilder) buildDropForeignKey(ctx *sql.Context, n *plan.DropForeignKey, row sql.Row) (sql.RowIter, error) {

sql/rowexec/dml_iters.go

@@ -610,9 +610,15 @@ func AddAccumulatorIter(ctx *sql.Context, iter sql.RowIter) (sql.RowIter, sql.Sc
 		return i.WithChildIter(childIter), sch
 	case *plan.TableEditorIter:
 		// If the TableEditorIter has RETURNING expressions, then we do NOT actually add the accumulatorIter
-		innerIter := i.InnerIter()
-		if insertIter, ok := innerIter.(*insertIter); ok && len(insertIter.returnExprs) > 0 {
-			return insertIter, insertIter.returnSchema
+		switch innerIter := i.InnerIter().(type) {
+		case *insertIter:
+			if len(innerIter.returnExprs) > 0 {
+				return innerIter, innerIter.returnSchema
+			}
+		case *updateIter:
+			if len(innerIter.returnExprs) > 0 {
+				return innerIter, innerIter.returnSchema
+			}
 		}
 
 		return defaultAccumulatorIter(ctx, iter)

sql/rowexec/update.go

@@ -23,12 +23,14 @@ import (
 )
 
 type updateIter struct {
-	childIter sql.RowIter
-	schema    sql.Schema
-	updater   sql.RowUpdater
-	checks    sql.CheckConstraints
-	closed    bool
-	ignore    bool
+	childIter    sql.RowIter
+	schema       sql.Schema
+	updater      sql.RowUpdater
+	checks       sql.CheckConstraints
+	closed       bool
+	ignore       bool
+	returnExprs  []sql.Expression
+	returnSchema sql.Schema
 }
 
 func (u *updateIter) Next(ctx *sql.Context) (sql.Row, error) {
@@ -66,6 +68,18 @@ func (u *updateIter) Next(ctx *sql.Context) (sql.Row, error) {
 				return nil, u.ignoreOrError(ctx, newRow, err)
 			}
 		}
+
+		if len(u.returnExprs) > 0 {
+			var retExprRow sql.Row
+			for _, returnExpr := range u.returnExprs {
+				result, err := returnExpr.Eval(ctx, newRow)
+				if err != nil {
+					return nil, err
+				}
+				retExprRow = append(retExprRow, result)
+			}
+			return retExprRow, nil
+		}
 	} else {
 		return nil, err
 	}
@@ -164,21 +178,27 @@ func newUpdateIter(
 	updater sql.RowUpdater,
 	checks sql.CheckConstraints,
 	ignore bool,
+	returnExprs []sql.Expression,
+	returnSchema sql.Schema,
 ) sql.RowIter {
 	if ignore {
 		return plan.NewCheckpointingTableEditorIter(&updateIter{
-			childIter: childIter,
-			updater:   updater,
-			schema:    schema,
-			checks:    checks,
-			ignore:    true,
+			childIter:    childIter,
+			updater:      updater,
+			schema:       schema,
+			checks:       checks,
+			ignore:       true,
+			returnExprs:  returnExprs,
+			returnSchema: returnSchema,
 		}, updater)
 	} else {
 		return plan.NewTableEditorIter(&updateIter{
-			childIter: childIter,
-			updater:   updater,
-			schema:    schema,
-			checks:    checks,
+			childIter:    childIter,
+			updater:      updater,
+			schema:       schema,
+			checks:       checks,
+			returnExprs:  returnExprs,
+			returnSchema: returnSchema,
 		}, updater)
 	}
 }