1 files changed, 14 insertions, 2 deletions
diff --git a/plan.go b/plan.go
index 9c4da54..9e9f44c 100644
--- a/plan.go
+++ b/plan.go
@@ -33,6 +33,7 @@ type plan struct {
 	// Planned queries.
 	Select plannedQuery // only `SELECT ... FROM ... WHERE `; user supplies the rest during Select{,One}Where()
 	Insert plannedQuery
+	Upsert plannedQuery
 	Update plannedQuery
 	Delete plannedQuery
 }
@@ -198,7 +199,8 @@ func buildPlan(t reflect.Type, dialect Dialect, opts planOpts) (plan, error) {
 
 	// prepare query strings
 	p.Select = p.buildSelectQueryIfPossible(dialect)
-	p.Insert = p.buildInsertQueryIfPossible(dialect)
+	p.Insert = p.buildInsertQueryIfPossible(dialect, false)
+	p.Upsert = p.buildInsertQueryIfPossible(dialect, true)
 	p.Update = p.buildUpdateQueryIfPossible(dialect)
 	p.Delete = p.buildDeleteQueryIfPossible(dialect)
 
@@ -247,7 +249,7 @@ func (p plan) buildSelectQueryIfPossible(dialect Dialect) plannedQuery {
 	return plannedQuery{query, nil, scanIndexes}
 }
 
-func (p plan) buildInsertQueryIfPossible(dialect Dialect) plannedQuery {
+func (p plan) buildInsertQueryIfPossible(dialect Dialect, isUpsert bool) plannedQuery {
 	if p.TableName == "" || len(p.AllColumnNames) == 0 {
 		return plannedQuery{Query: ""}
 	}
@@ -256,6 +258,13 @@ func (p plan) buildInsertQueryIfPossible(dialect Dialect) plannedQuery {
 		return plannedQuery{Query: ""}
 	}
 
+	// UPSERT queries specifically are only generated if we have non-auto primary keys:
+	// - cannot hit a key conflict if there are no keys
+	// - cannot hit a key conflict on insert if all keys are autogenerated (and thus we never supply them during INSERT)
+	if isUpsert && !slices.ContainsFunc(p.PrimaryKeyColumnNames, func(n string) bool { return !slices.Contains(p.AutoColumnNames, n) }) {
+		return plannedQuery{Query: ""}
+	}
+
 	var (
 		argumentIndexes    = make([][]int, len(nonAutoColumnNames))
 		scanIndexes        [][]int
@@ -282,6 +291,9 @@ func (p plan) buildInsertQueryIfPossible(dialect Dialect) plannedQuery {
 		strings.Join(quotedColumnNames, ", "),
 		strings.Join(quotedPlaceholders, ", "),
 	)
+	if isUpsert {
+		query += dialect.UpsertClause(p.PrimaryKeyColumnNames, p.getNonPrimaryKeyColumnNames())
+	}
 	if len(p.AutoColumnNames) > 0 {
 		query += dialect.InsertSuffixForAutoColumns(p.AutoColumnNames)
 	}