CLICKHOUSE-1194: add skipping index to the beginning of the list

add the FIRST keyword to the ADD INDEX command to be able to add index in the beginning of the list.

Signed-off-by: Aleksei Semiglazov <asemiglazov@cloudflare.com>

docs/en/sql-reference/statements/alter/index/index.md

@@ -8,7 +8,7 @@ toc_title: INDEX
 
 The following operations are available:
 
--   `ALTER TABLE [db].name ADD INDEX name expression TYPE type GRANULARITY value AFTER name [AFTER name2]` - Adds index description to tables metadata.
+-   `ALTER TABLE [db].name ADD INDEX name expression TYPE type GRANULARITY value [FIRST|AFTER name]` - Adds index description to tables metadata.
 
 -   `ALTER TABLE [db].name DROP INDEX name` - Removes index description from tables metadata and deletes index files from disk.
 

docs/ja/sql-reference/statements/alter.md

@@ -175,7 +175,7 @@ MODIFY ORDER BY new_expression
 [複製](../../engines/table-engines/mergetree-family/replication.md) テーブル）。 次の操作
 利用できます:
 
--   `ALTER TABLE [db].name ADD INDEX name expression TYPE type GRANULARITY value AFTER name [AFTER name2]` -付加価指数の説明をテーブルメタデータを指すものとします。
+-   `ALTER TABLE [db].name ADD INDEX name expression TYPE type GRANULARITY value [FIRST|AFTER name]` -付加価指数の説明をテーブルメタデータを指すものとします。
 
 -   `ALTER TABLE [db].name DROP INDEX name` -除去す指標の説明からテーブルメタデータを削除を行指数のファイルからディスク。
 

docs/ru/sql-reference/statements/alter/index/index.md

@@ -9,7 +9,7 @@ toc_title: "Манипуляции с индексами"
 Добавить или удалить индекс можно с помощью операций
 
 ``` sql
-ALTER TABLE [db.]name ADD INDEX name expression TYPE type GRANULARITY value [AFTER name]
+ALTER TABLE [db.]name ADD INDEX name expression TYPE type GRANULARITY value [FIRST|AFTER name]
 ALTER TABLE [db.]name DROP INDEX name
 ALTER TABLE [db.]table MATERIALIZE INDEX name IN PARTITION partition_name
 ```

docs/zh/sql-reference/statements/alter.md

@@ -174,7 +174,7 @@ MODIFY ORDER BY new_expression
 该操作仅支持 [`MergeTree`](../../engines/table-engines/mergetree-family/mergetree.md) 系列表 (含 [replicated](../../engines/table-engines/mergetree-family/replication.md) 表)。
 下列操作是允许的：
 
--   `ALTER TABLE [db].name ADD INDEX name expression TYPE type GRANULARITY value AFTER name [AFTER name2]` - 在表的元数据中增加索引说明
+-   `ALTER TABLE [db].name ADD INDEX name expression TYPE type GRANULARITY value [FIRST|AFTER name]` - 在表的元数据中增加索引说明
 
 -   `ALTER TABLE [db].name DROP INDEX name` - 从表的元数据中删除索引描述，并从磁盘上删除索引文件
 

src/Parsers/ASTAlterQuery.cpp

@@ -137,8 +137,9 @@ void ASTAlterCommand::formatImpl(
         settings.ostr << (settings.hilite ? hilite_keyword : "") << indent_str << "ADD INDEX " << (if_not_exists ? "IF NOT EXISTS " : "") << (settings.hilite ? hilite_none : "");
         index_decl->formatImpl(settings, state, frame);
 
-        /// AFTER
-        if (index)
+        if (first)
+            settings.ostr << (settings.hilite ? hilite_keyword : "") << indent_str << " FIRST " << (settings.hilite ? hilite_none : "");
+        else if (index)    /// AFTER
         {
             settings.ostr << (settings.hilite ? hilite_keyword : "") << indent_str << " AFTER " << (settings.hilite ? hilite_none : "");
             index->formatImpl(settings, state, frame);

src/Parsers/ParserAlterQuery.cpp

@@ -231,7 +231,9 @@ bool ParserAlterCommand::parseImpl(Pos & pos, ASTPtr & node, Expected & expected
             if (!parser_idx_decl.parse(pos, command->index_decl, expected))
                 return false;
 
-            if (s_after.ignore(pos, expected))
+            if (s_first.ignore(pos, expected))
+                command->first = true;
+            else if (s_after.ignore(pos, expected))
             {
                 if (!parser_name.parse(pos, command->index, expected))
                     return false;

src/Storages/AlterCommands.cpp

@@ -211,6 +211,7 @@ std::optional<AlterCommand> AlterCommand::parse(const ASTAlterCommand * command_
             command.after_index_name = command_ast->index->as<ASTIdentifier &>().name();
 
         command.if_not_exists = command_ast->if_not_exists;
+        command.first = command_ast->first;
 
         return command;
     }
@@ -454,6 +455,10 @@ void AlterCommand::apply(StorageInMemoryMetadata & metadata, ContextPtr context)
 
         auto insert_it = metadata.secondary_indices.end();
 
+        /// insert the index in the beginning of the indices list
+        if (first)
+            insert_it = metadata.secondary_indices.begin();
+
         if (!after_index_name.empty())
         {
             insert_it = std::find_if(

src/Storages/AlterCommands.h

@@ -77,7 +77,7 @@ struct AlterCommand
     /// For ADD or MODIFY - after which column to add a new one. If an empty string, add to the end.
     String after_column;
 
-    /// For ADD_COLUMN, MODIFY_COLUMN - Add to the begin if it is true.
+    /// For ADD_COLUMN, MODIFY_COLUMN, ADD_INDEX - Add to the begin if it is true.
     bool first = false;
 
     /// For DROP_COLUMN, MODIFY_COLUMN, COMMENT_COLUMN

tests/queries/0_stateless/01932_alter_index_with_order.reference

@@ -0,0 +1,9 @@
+default	alter_index_test	index_a	set	a	1
+default	alter_index_test	index_b	minmax	b	1
+default	alter_index_test	index_c	set	c	2
+default	alter_index_test	index_a	set	a	1
+default	alter_index_test	index_d	set	d	1
+default	alter_index_test	index_b	minmax	b	1
+default	alter_index_test	index_c	set	c	2
+default	alter_index_test	index_a	set	a	1
+default	alter_index_test	index_d	set	d	1

tests/queries/0_stateless/01932_alter_index_with_order.sql

@@ -0,0 +1,28 @@
+DROP TABLE IF EXISTS alter_index_test;
+
+CREATE TABLE alter_index_test (
+    a UInt32,
+    b Date,
+    c UInt32,
+    d UInt32,
+    INDEX index_a a TYPE set(0) GRANULARITY 1
+)
+ENGINE = MergeTree()
+ORDER BY tuple();
+
+SELECT * FROM system.data_skipping_indices WHERE table = 'alter_index_test' AND database = currentDatabase();
+
+ALTER TABLE alter_index_test ADD INDEX index_b b type minmax granularity 1 FIRST;
+
+ALTER TABLE alter_index_test ADD INDEX index_c c type set(0) granularity 2 AFTER index_b;
+
+ALTER TABLE alter_index_test ADD INDEX index_d d type set(0) granularity 1;
+
+SELECT * FROM system.data_skipping_indices WHERE table = 'alter_index_test' AND database = currentDatabase();
+
+DETACH TABLE alter_index_test;
+ATTACH TABLE alter_index_test;
+
+SELECT * FROM system.data_skipping_indices WHERE table = 'alter_index_test' AND database = currentDatabase();
+
+DROP TABLE IF EXISTS alter_index_test;