Support conditional ON CONFLICT updates

server/analyzer/assign_insert_casts.go

@@ -120,8 +120,13 @@ func AssignInsertCasts(ctx *sql.Context, a *analyzer.Analyzer, node sql.Node, sc
 		if err != nil {
 			return nil, false, err
 		}
+		exprs := append(newDupExprs, insertInto.Checks().ToExpressions()...)
+		if insertInto.OnDupWhere != nil {
+			exprs = append(exprs, insertInto.OnDupWhere)
+		}
+		exprs = append(exprs, insertInto.Returning...)
 		// TODO: this relies on a particular implementation detail InsertInto.WithExpressions
-		newInsertInto, err := insertInto.WithExpressions(ctx, append(newDupExprs, insertInto.Checks().ToExpressions()...)...)
+		newInsertInto, err := insertInto.WithExpressions(ctx, exprs...)
 		if err != nil {
 			return nil, false, err
 		}

server/ast/insert.go

@@ -41,6 +41,7 @@ func nodeInsert(ctx *Context, node *tree.Insert) (insert *vitess.Insert, err err
 	}
 	var ignore string
 	var onDuplicate vitess.OnDup
+	var onDuplicateWhere vitess.Expr
 
 	if node.OnConflict != nil {
 		if isIgnore(node.OnConflict) {
@@ -54,6 +55,12 @@ func nodeInsert(ctx *Context, node *tree.Insert) (insert *vitess.Insert, err err
 			for _, updateExpr := range updateExprs {
 				onDuplicate = append(onDuplicate, updateExpr)
 			}
+			if node.OnConflict.Where != nil {
+				onDuplicateWhere, err = nodeExpr(ctx, node.OnConflict.Where.Expr)
+				if err != nil {
+					return nil, err
+				}
+			}
 		} else {
 			return nil, errors.Errorf("the ON CONFLICT clause provided is not yet supported")
 		}
@@ -107,14 +114,19 @@ func nodeInsert(ctx *Context, node *tree.Insert) (insert *vitess.Insert, err err
 		}
 	}
 	return &vitess.Insert{
-		Action:    vitess.InsertStr,
-		Ignore:    ignore,
-		Table:     tableName,
-		Returning: returningExprs,
-		With:      with,
-		Columns:   columns,
-		Rows:      rows,
-		OnDup:     onDuplicate,
+		Action:           vitess.InsertStr,
+		Ignore:           ignore,
+		Table:            tableName,
+		Returning:        returningExprs,
+		With:             with,
+		Columns:          columns,
+		Rows:             rows,
+		OnDup:            onDuplicate,
+		OnDupValuesAlias: "excluded",
+		OnDupWhere:       onDuplicateWhere,
+		// TODO: Apply PostgreSQL's single-row count to unconditional conflict updates once
+		//       enginetests support dialect-specific affected-row expectations.
+		CountOnDuplicateUpdateAsOneRow: node.OnConflict != nil && node.OnConflict.Where != nil,
 		Auth: vitess.AuthInformation{
 			AuthType:    auth.AuthType_INSERT,
 			TargetType:  auth.AuthTargetType_TableIdentifiers,
@@ -134,11 +146,5 @@ func isIgnore(conflict *tree.OnConflict) bool {
 // supportedOnConflictClause returns true if the ON CONFLICT clause given can be represented as
 // an ON DUPLICATE KEY UPDATE clause in GMS
 func supportedOnConflictClause(conflict *tree.OnConflict) bool {
-	if conflict.ArbiterPredicate != nil {
-		return false
-	}
-	if conflict.Where != nil {
-		return false
-	}
-	return true
+	return conflict.ArbiterPredicate == nil
 }