From 616b9cd948e9d2730fb7c7446537a5cc6bd3f39e Mon Sep 17 00:00:00 2001
From: Stanislav Tebloev <stebloev@ydb.tech>
Date: Tue, 11 Nov 2025 12:15:57 +0000
Subject: [PATCH 1/2] Add n-gram kqp tests

---
 .../ut/indexes/kqp_indexes_fulltext_ut.cpp    | 93 +++++++++++++++++++
 1 file changed, 93 insertions(+)

diff --git a/ydb/core/kqp/ut/indexes/kqp_indexes_fulltext_ut.cpp b/ydb/core/kqp/ut/indexes/kqp_indexes_fulltext_ut.cpp
index 229d5f5fa6c5..176aa2e91ff5 100644
--- a/ydb/core/kqp/ut/indexes/kqp_indexes_fulltext_ut.cpp
+++ b/ydb/core/kqp/ut/indexes/kqp_indexes_fulltext_ut.cpp
@@ -61,6 +61,24 @@ void AddIndex(NQuery::TQueryClient& db) {
     UNIT_ASSERT_VALUES_EQUAL_C(result.GetStatus(), EStatus::SUCCESS, result.GetIssues().ToString());
 }
 
+void AddIndexNGram(NQuery::TQueryClient& db, const size_t nGramMinLength = 3, const size_t nGramMaxLength = 3, const bool edgeNGram = false) {
+    const TString query = Sprintf(R"sql(
+        ALTER TABLE `/Root/Texts` ADD INDEX fulltext_idx
+            GLOBAL USING fulltext
+            ON (Text)
+            WITH (
+                layout=flat,
+                tokenizer=standard,
+                use_filter_ngram=%d,
+                use_filter_edge_ngram=%d,
+                filter_ngram_min_length=%d,
+                filter_ngram_max_length=%d
+            );
+    )sql", !edgeNGram, edgeNGram, nGramMinLength, nGramMaxLength);
+    auto result = db.ExecuteQuery(query, NYdb::NQuery::TTxControl::NoTx()).ExtractValueSync();
+    UNIT_ASSERT_VALUES_EQUAL_C(result.GetStatus(), EStatus::SUCCESS, result.GetIssues().ToString());
+}
+
 void AddIndexCovered(NQuery::TQueryClient& db) {
     TString query = R"sql(
         ALTER TABLE `/Root/Texts` ADD INDEX fulltext_idx
@@ -131,6 +149,81 @@ Y_UNIT_TEST(AddIndexCovered) {
     ])", NYdb::FormatResultSetYson(index));
 }
 
+Y_UNIT_TEST(AddIndexNGram) {
+    auto kikimr = Kikimr();
+    auto db = kikimr.GetQueryClient();
+    
+    CreateTexts(db);
+    UpsertTexts(db);
+    AddIndexNGram(db);
+
+    const auto index = ReadIndex(db);
+    CompareYson(R"([
+        [[100u];"Cat"];
+        [[300u];"Cat"];
+        [[200u];"Dog"];
+        [[400u];"Fox"];
+        [[100u];"all"];
+        [[200u];"all"];
+        [[100u];"als"];
+        [[100u];"ani"];
+        [[100u];"ase"];
+        [[200u];"ase"];
+        [[100u];"ats"];
+        [[200u];"ats"];
+        [[300u];"ats"];
+        [[200u];"cat"];
+        [[300u];"cat"];
+        [[100u];"cha"];
+        [[200u];"cha"];
+        [[400u];"dog"];
+        [[100u];"has"];
+        [[200u];"has"];
+        [[100u];"ima"];
+        [[300u];"lov"];
+        [[400u];"lov"];
+        [[100u];"mal"];
+        [[200u];"mal"];
+        [[100u];"nim"];
+        [[200u];"ogs"];
+        [[400u];"ogs"];
+        [[300u];"ove"];
+        [[400u];"ove"];
+        [[400u];"oxe"];
+        [[100u];"sma"];
+        [[200u];"sma"];
+        [[400u];"xes"]
+    ])", NYdb::FormatResultSetYson(index));
+}
+
+Y_UNIT_TEST(AddIndexEdgeNGram) {
+    auto kikimr = Kikimr();
+    auto db = kikimr.GetQueryClient();
+    
+    CreateTexts(db);
+    UpsertTexts(db);
+    AddIndexNGram(db, 3, 3, true);
+
+    const auto index = ReadIndex(db);
+    Cerr << NYdb::FormatResultSetYson(index) << Endl;
+    CompareYson(R"([
+        [[100u];"Cat"];
+        [[300u];"Cat"];
+        [[200u];"Dog"];
+        [[400u];"Fox"];
+        [[100u];"ani"];
+        [[200u];"cat"];
+        [[300u];"cat"];
+        [[100u];"cha"];
+        [[200u];"cha"];
+        [[400u];"dog"];
+        [[300u];"lov"];
+        [[400u];"lov"];
+        [[100u];"sma"];
+        [[200u];"sma"]
+    ])", NYdb::FormatResultSetYson(index));
+}
+
 Y_UNIT_TEST(InsertRow) {
     auto kikimr = Kikimr();
     auto db = kikimr.GetQueryClient();

From dbc8196c5c5b67d5e7de356ff3cf69a6eb3c0682 Mon Sep 17 00:00:00 2001
From: Stanislav Tebloev <stebloev@ydb.tech>
Date: Thu, 13 Nov 2025 11:02:15 +0000
Subject: [PATCH 2/2] Use lowercase filter

---
 .../kqp/ut/indexes/kqp_indexes_fulltext_ut.cpp   | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/ydb/core/kqp/ut/indexes/kqp_indexes_fulltext_ut.cpp b/ydb/core/kqp/ut/indexes/kqp_indexes_fulltext_ut.cpp
index 176aa2e91ff5..80d08eb29b3e 100644
--- a/ydb/core/kqp/ut/indexes/kqp_indexes_fulltext_ut.cpp
+++ b/ydb/core/kqp/ut/indexes/kqp_indexes_fulltext_ut.cpp
@@ -69,6 +69,7 @@ void AddIndexNGram(NQuery::TQueryClient& db, const size_t nGramMinLength = 3, co
             WITH (
                 layout=flat,
                 tokenizer=standard,
+                use_filter_lowercase=true,
                 use_filter_ngram=%d,
                 use_filter_edge_ngram=%d,
                 filter_ngram_min_length=%d,
@@ -158,11 +159,8 @@ Y_UNIT_TEST(AddIndexNGram) {
     AddIndexNGram(db);
 
     const auto index = ReadIndex(db);
+
     CompareYson(R"([
-        [[100u];"Cat"];
-        [[300u];"Cat"];
-        [[200u];"Dog"];
-        [[400u];"Fox"];
         [[100u];"all"];
         [[200u];"all"];
         [[100u];"als"];
@@ -172,11 +170,14 @@ Y_UNIT_TEST(AddIndexNGram) {
         [[100u];"ats"];
         [[200u];"ats"];
         [[300u];"ats"];
+        [[100u];"cat"];
         [[200u];"cat"];
         [[300u];"cat"];
         [[100u];"cha"];
         [[200u];"cha"];
+        [[200u];"dog"];
         [[400u];"dog"];
+        [[400u];"fox"];
         [[100u];"has"];
         [[200u];"has"];
         [[100u];"ima"];
@@ -207,16 +208,15 @@ Y_UNIT_TEST(AddIndexEdgeNGram) {
     const auto index = ReadIndex(db);
     Cerr << NYdb::FormatResultSetYson(index) << Endl;
     CompareYson(R"([
-        [[100u];"Cat"];
-        [[300u];"Cat"];
-        [[200u];"Dog"];
-        [[400u];"Fox"];
         [[100u];"ani"];
+        [[100u];"cat"];
         [[200u];"cat"];
         [[300u];"cat"];
         [[100u];"cha"];
         [[200u];"cha"];
+        [[200u];"dog"];
         [[400u];"dog"];
+        [[400u];"fox"];
         [[300u];"lov"];
         [[400u];"lov"];
         [[100u];"sma"];