Fix point lookup bug w/ prefix matching secondary (#5670)

* Fix point lookup bug w/ prefix matching secondary

* docstring

go/libraries/doltcore/sqle/index/index_lookup.go

@@ -260,6 +260,7 @@ func NewLookupBuilder(
 		base.sec = durable.ProllyMapFromIndex(s.Secondary)
 		base.secKd, base.secVd = base.sec.Descriptors()
 		base.ns = base.sec.NodeStore()
+		base.prefDesc = base.secKd.PrefixDesc(len(di.columns))
 	}
 
 	switch {
@@ -330,6 +331,7 @@ type baseLookupBuilder struct {
 
 	sec          prolly.Map
 	secKd, secVd val.TupleDesc
+	prefDesc     val.TupleDesc
 	ns           tree.NodeStore
 }
 
@@ -346,7 +348,7 @@ func (lb *baseLookupBuilder) NewRowIter(ctx *sql.Context, part sql.Partition) (s
 // every subsequent point lookup. Note that equality joins can have a mix of
 // point lookups on concrete values, and range lookups for null matches.
 func (lb *baseLookupBuilder) newPointLookup(ctx *sql.Context, rang prolly.Range) (iter prolly.MapIter, err error) {
-	err = lb.sec.Get(ctx, rang.Tup, func(key val.Tuple, value val.Tuple) (err error) {
+	err = lb.sec.GetPrefix(ctx, rang.Tup, lb.prefDesc, func(key val.Tuple, value val.Tuple) (err error) {
 		if key != nil && rang.Matches(key) {
 			iter = prolly.NewPointLookup(key, value)
 		} else {

go/store/prolly/tree/map.go

@@ -237,6 +237,26 @@ func (t StaticMap[K, V, O]) Get(ctx context.Context, query K, cb KeyValueFn[K, V
 	return cb(key, value)
 }
 
+func (t StaticMap[K, V, O]) GetPrefix(ctx context.Context, query K, prefixOrder O, cb KeyValueFn[K, V]) (err error) {
+	cur, err := newLeafCursorAtKey(ctx, t.NodeStore, t.Root, query, t.Order)
+	if err != nil {
+		return err
+	}
+
+	var key K
+	var value V
+
+	if cur.Valid() {
+		key = K(cur.CurrentKey())
+		if prefixOrder.Compare(query, key) == 0 {
+			value = V(cur.currentValue())
+		} else {
+			key = nil
+		}
+	}
+	return cb(key, value)
+}
+
 func (t StaticMap[K, V, O]) Has(ctx context.Context, query K) (ok bool, err error) {
 	cur, err := newLeafCursorAtKey(ctx, t.NodeStore, t.Root, query, t.Order)
 	if err != nil {

go/store/prolly/tuple_map.go

@@ -246,6 +246,12 @@ func (m Map) Get(ctx context.Context, key val.Tuple, cb tree.KeyValueFn[val.Tupl
 	return m.tuples.Get(ctx, key, cb)
 }
 
+// GetPrefix returns the first key-value pair that matches the prefix key
+// or nil to the callback.
+func (m Map) GetPrefix(ctx context.Context, key val.Tuple, prefDesc val.TupleDesc, cb tree.KeyValueFn[val.Tuple, val.Tuple]) (err error) {
+	return m.tuples.GetPrefix(ctx, key, prefDesc, cb)
+}
+
 // Has returns true is |key| is present in the Map.
 func (m Map) Has(ctx context.Context, key val.Tuple) (ok bool, err error) {
 	return m.tuples.Has(ctx, key)