sql: make global indexes a new doc and add more contents

TOC-tidb-cloud.md

@@ -625,6 +625,7 @@
     - [Set Operations](/functions-and-operators/set-operators.md)
     - [List of Expressions for Pushdown](/functions-and-operators/expressions-pushed-down.md)
   - [Clustered Indexes](/clustered-indexes.md)
+  - [Global Indexes](/global-indexes.md)
   - [Constraints](/constraints.md)
   - [Generated Columns](/generated-columns.md)
   - [SQL Mode](/sql-mode.md)

TOC.md

@@ -984,6 +984,7 @@
       - [List of Expressions for Pushdown](/functions-and-operators/expressions-pushed-down.md)      
       - [Comparisons between Functions and Syntax of Oracle and TiDB](/oracle-functions-to-tidb.md)
     - [Clustered Indexes](/clustered-indexes.md)
+    - [Global Indexes](/global-indexes.md)
     - [Vector Index](/vector-search/vector-search-index.md)
     - [Constraints](/constraints.md)
     - [Generated Columns](/generated-columns.md)

basic-features.md

@@ -66,7 +66,7 @@ You can try out TiDB features on [TiDB Playground](https://play.tidbcloud.com/?u
 | [Multi-valued indexes](/sql-statements/sql-statement-create-index.md#multi-valued-indexes) | Y | Y | Y | Y | N | N | N |
 | [Foreign key](/foreign-key.md) | Y | E | E | E | N | N | N |
 | [TiFlash late materialization](/tiflash/tiflash-late-materialization.md) | Y | Y | Y | Y | N | N | N |
-| [Global index](/partitioned-table.md#global-indexes) | Y |  N | N  | N | N | N | N |
+| [Global index](/global-indexes.md) | Y |  N | N  | N | N | N | N |
 | [Vector index](/vector-search/vector-search-index.md) | E | N | N | N | N | N | N |
 
 ## SQL statements
@@ -174,7 +174,7 @@ You can try out TiDB features on [TiDB Playground](https://play.tidbcloud.com/?u
 | [Range INTERVAL partitioning](/partitioned-table.md#range-interval-partitioning) | Y | Y | Y | Y | E | N | N |
 | [Convert a partitioned table to a non-partitioned table](/partitioned-table.md#convert-a-partitioned-table-to-a-non-partitioned-table) | Y | Y | Y | N | N | N | N |
 | [Partition an existing table](/partitioned-table.md#partition-an-existing-table) | Y | Y | Y | N | N | N | N |
-| [Global index](/partitioned-table.md#global-indexes) | Y | N | N | N | N | N | N |
+| [Global indexes](/global-indexes.md) | Y | N | N | N | N | N | N |
 
 ## Statistics
 

best-practices/tidb-best-practices.md

@@ -81,7 +81,7 @@
 
 ### Secondary index
 
-TiDB supports the complete secondary indexes, which are also global indexes. Many queries can be optimized by index. Thus, it is important for applications to make good use of secondary indexes.
+TiDB supports the complete secondary indexes, which are also [global indexes](/global-indexes.md). Many queries can be optimized by index. Thus, it is important for applications to make good use of secondary indexes.
 
 Lots of MySQL experience is also applicable to TiDB. It is noted that TiDB has its unique features. The following are a few notes when using secondary indexes in TiDB.
 

choose-index.md

@@ -81,7 +81,7 @@ Skyline-pruning is a heuristic filtering rule for indexes, which can reduce the
 
 - Select whether the index satisfies a certain order. Because index reading can guarantee the order of certain column sets, indexes that satisfy the query order are superior to indexes that do not satisfy on this dimension.
 
-- Whether the index is a [global index](/partitioned-table.md#global-indexes). In partitioned tables, global indexes can effectively reduce the number of cop tasks for a SQL compared to normal indexes, thus improving overall performance.
+- Whether the index is a [global index](global-indexes.md). In partitioned tables, global indexes can effectively reduce the number of cop tasks for a SQL compared to normal indexes, thus improving overall performance.
 
 For these preceding dimensions, if the index `idx_a` performs no worse than the index `idx_b` in all three dimensions and performs better than `idx_b` in one dimension, then `idx_a` is preferred. When executing the `EXPLAIN FORMAT = 'verbose' ...` statement, if skyline-pruning excludes some indexes, TiDB outputs a NOTE-level warning listing the remaining indexes after the skyline-pruning exclusion.
 

partitioned-table.md

@@ -1197,7 +1197,7 @@ ALTER TABLE member_level PARTITION BY RANGE(level)
  PARTITION pMax VALUES LESS THAN (MAXVALUE));
 ```
 
-When partitioning a non-partitioned table or repartitioning an already partitioned table, you can update the indexes to be global or local as needed:
+When partitioning a non-partitioned table or repartitioning an already partitioned table, you can update the indexes to be [global indexes](/global-indexes.md) or local indexes as needed:
 
 ```sql
 CREATE TABLE t1 (
@@ -1491,7 +1491,7 @@ This section discusses the relationship of partitioning keys with primary keys a
 
 > **Note:**
 >
-> You can ignore this rule when using [global indexes](#global-indexes).
+> You can ignore this rule when using [global indexes](/global-indexes.md).
 
 For example, the following table creation statements are invalid:
 
@@ -1702,103 +1702,7 @@ ERROR 8264 (HY000): Global Index is needed for index 'a', since the unique index
 
 ### Global indexes
 
-Before the introduction of global indexes, TiDB created a local index for each partition, leading to [a limitation](#partitioning-keys-primary-keys-and-unique-keys) that primary keys and unique keys had to include the partition key to ensure data uniqueness. Additionally, when querying data across multiple partitions, TiDB needed to scan the data of each partition to return results.
-
-To address these issues, TiDB introduces the global indexes feature in v8.3.0. A global index covers the data of the entire table with a single index, allowing primary keys and unique keys to maintain global uniqueness without including all partition keys. Moreover, global indexes can access index data across multiple partitions in a single operation instead of looking up the local index for each partition, significantly improving query performance for non-partitioned keys. Starting from v9.0.0, non-unique indexes can also be created as global indexes.
-
-To create a global index, you can add the `GLOBAL` keyword in the index definition.
-
-> **Note:**
->
-> Global indexes affect partition management. `DROP`, `TRUNCATE`, and `REORGANIZE PARTITION` operations also trigger updates to table-level global indexes, meaning that these DDL operations will only return results after the global indexes of the corresponding tables are fully updated.
-
-```sql
-CREATE TABLE t1 (
-    col1 INT NOT NULL,
-    col2 DATE NOT NULL,
-    col3 INT NOT NULL,
-    col4 INT NOT NULL,
-    UNIQUE KEY uidx12(col1, col2) GLOBAL,
-    UNIQUE KEY uidx3(col3),
-    KEY idx1(col1) GLOBAL
-)
-PARTITION BY HASH(col3)
-PARTITIONS 4;
-```
-
-In the preceding example, the unique index `uidx12` and non-unique index `idx1` are global indexes, while `uidx3` is a regular unique index.
-
-Note that a **clustered index** cannot be a global index, as shown in the following example:
-
-```sql
-CREATE TABLE t2 (
-    col1 INT NOT NULL,
-    col2 DATE NOT NULL,
-    PRIMARY KEY (col2) CLUSTERED GLOBAL
-) PARTITION BY HASH(col1) PARTITIONS 5;
-```
-
-```
-ERROR 1503 (HY000): A CLUSTERED INDEX must include all columns in the table's partitioning function
-```
-
-The reason is that if the clustered index is a global index, the table will no longer be partitioned. This is because the key of the clustered index is also the record key at the partition level, but the global index is at the table level, which causes a conflict. If you need to set the primary key as a global index, you must explicitly define it as a non-clustered index, for example, `PRIMARY KEY(col1, col2) NONCLUSTERED GLOBAL`.
-
-You can identify a global index by the `GLOBAL` index option in the [`SHOW CREATE TABLE`](/sql-statements/sql-statement-show-create-table.md) output.
-
-```sql
-SHOW CREATE TABLE t1\G
-```
-
-```
-       Table: t1
-Create Table: CREATE TABLE `t1` (
-  `col1` int NOT NULL,
-  `col2` date NOT NULL,
-  `col3` int NOT NULL,
-  `col4` int NOT NULL,
-  UNIQUE KEY `uidx12` (`col1`,`col2`) /*T![global_index] GLOBAL */,
-  UNIQUE KEY `uidx3` (`col3`),
-  KEY `idx1` (`col1`) /*T![global_index] GLOBAL */
-) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin
-PARTITION BY HASH (`col3`) PARTITIONS 4
-1 row in set (0.00 sec)
-```
-
-Alternatively, you can query the [`INFORMATION_SCHEMA.TIDB_INDEXES`](/information-schema/information-schema-tidb-indexes.md) table and check the `IS_GLOBAL` column in the output.
-
-```sql
-SELECT * FROM INFORMATION_SCHEMA.TIDB_INDEXES WHERE table_name='t1';
-```
-
-```
-+--------------+------------+------------+----------+--------------+-------------+----------+---------------+------------+----------+------------+-----------+-----------+
-| TABLE_SCHEMA | TABLE_NAME | NON_UNIQUE | KEY_NAME | SEQ_IN_INDEX | COLUMN_NAME | SUB_PART | INDEX_COMMENT | Expression | INDEX_ID | IS_VISIBLE | CLUSTERED | IS_GLOBAL |
-+--------------+------------+------------+----------+--------------+-------------+----------+---------------+------------+----------+------------+-----------+-----------+
-| test         | t1         |          0 | uidx12   |            1 | col1        |     NULL |               | NULL       |        1 | YES        | NO        |         1 |
-| test         | t1         |          0 | uidx12   |            2 | col2        |     NULL |               | NULL       |        1 | YES        | NO        |         1 |
-| test         | t1         |          0 | uidx3    |            1 | col3        |     NULL |               | NULL       |        2 | YES        | NO        |         0 |
-| test         | t1         |          1 | idx1     |            1 | col1        |     NULL |               | NULL       |        3 | YES        | NO        |         1 |
-+--------------+------------+------------+----------+--------------+-------------+----------+---------------+------------+----------+------------+-----------+-----------+
-3 rows in set (0.00 sec)
-```
-
-When partitioning a non-partitioned table or repartitioning an already partitioned table, you can update the indexes to be global indexes or local indexes as needed.
-
-For example, the following SQL statement repartitions table `t1` based on the `col1` column, updates the global indexes `uidx12` and `idx1` to local indexes, and updates the local index `uidx3` to a global index. Because `uidx3` is a unique index on the `col3` column, it must be a global index to ensure the uniqueness of `col3` across all partitions. `uidx12` and `idx1` are indexes on the `col1` column, which means they can be either global or local indexes. 
-
-```sql
-ALTER TABLE t1 PARTITION BY HASH (col1) PARTITIONS 3 UPDATE INDEXES (uidx12 LOCAL, uidx3 GLOBAL, idx1 LOCAL);
-```
-
-#### Limitations of global indexes
-
-- If the `GLOBAL` keyword is not explicitly specified in the index definition, TiDB creates a local index by default.
-- The `GLOBAL` and `LOCAL` keywords only apply to partitioned tables and do not affect non-partitioned tables. In other words, there is no difference between a global index and a local index in non-partitioned tables.
-- DDL operations such as `DROP PARTITION`, `TRUNCATE PARTITION`, and `REORGANIZE PARTITION` also trigger updates to global indexes. These DDL operations need to wait for the global index updates to complete before returning results, which increases the execution time accordingly. This is particularly evident in data archiving scenarios, such as `DROP PARTITION` and `TRUNCATE PARTITION`. Without global indexes, these operations can typically complete immediately. However, with global indexes, the execution time increases as the number of indexes that need to be updated grows.
-- Tables with global indexes do not support the `EXCHANGE PARTITION` operation.
-- By default, the primary key of a partitioned table is a clustered index and must include the partition key. If you require the primary key to exclude the partition key, you can explicitly specify the primary key as a non-clustered global index when creating the table, for example, `PRIMARY KEY(col1, col2) NONCLUSTERED GLOBAL`.
-- If a global index is added to an expression column, or a global index is also a prefix index (for example `UNIQUE KEY idx_id_prefix (id(10)) GLOBAL`), you need to collect statistics manually for this global index.
+For more information about global indexes, see [Global Indexes](/global-indexes.md).
 
 ### Partitioning limitations relating to functions
 

placement-rules-in-sql.md

@@ -312,7 +312,7 @@ PARTITION BY RANGE( YEAR(purchased) ) (
 );
 ```
 
-If no placement policy is specified for a partition in a table, the partition attempts to inherit the policy (if any) from the table. If the table has a [global index](/partitioned-table.md#global-indexes), the index will apply the same placement policy as the table. In the preceding example:
+If no placement policy is specified for a partition in a table, the partition attempts to inherit the policy (if any) from the table. If the table has a [global index](/global-indexes.md), the index will apply the same placement policy as the table. In the preceding example:
 
 - The `p0` partition will apply the `storageforhistorydata` policy.
 - The `p4` partition will apply the `storagefornewdata` policy.

releases/release-8.3.0.md

@@ -119,7 +119,7 @@ Quick access: [Quick start](https://docs.pingcap.com/tidb/v8.3/quick-start-with-
 
     Starting with v8.3.0, the global index feature is released as an experimental feature. You can explicitly create a global index for a partitioned table with the keyword `Global` to remove the restriction that the unique key must use every column in the table's partitioning expression, to meet flexible business needs. Global indexes also enhance the performance of queries that do not include partition keys.
 
-    For more information, see [documentation](/partitioned-table.md#global-indexes).
+    For more information, see [documentation](/global-indexes.md).
 
 ### Reliability
 

releases/release-8.4.0.md

@@ -134,7 +134,7 @@ Quick access: [Quick start](https://docs.pingcap.com/tidb/v8.4/quick-start-with-
 
     In v8.4.0, this feature becomes generally available (GA). You can use the keyword `GLOBAL` to create a global index, instead of setting the system variable [`tidb_enable_global_index`](/system-variables.md#tidb_enable_global_index-new-in-v760) to enable the global index feature. Starting from v8.4.0, this system variable is deprecated and is always `ON`.
 
-    For more information, see [documentation](/partitioned-table.md#global-indexes).
+    For more information, see [documentation](/global-indexes.md).
 
 * Improve query performance for cached tables in some scenarios [#43249](https://github.com/pingcap/tidb/issues/43249) @[tiancaiamao](https://github.com/tiancaiamao)
 
@@ -282,7 +282,7 @@ Quick access: [Quick start](https://docs.pingcap.com/tidb/v8.4/quick-start-with-
 |--------|------------------------------|------|
 | `log_bin` | Deleted | In v8.4.0, [TiDB Binlog](https://docs.pingcap.com/tidb/v8.3/tidb-binlog-overview) is removed. This variable indicates whether TiDB Binlog is used, and is deleted starting from v8.4.0. |
 | `sql_log_bin` | Deleted | In v8.4.0, [TiDB Binlog](https://docs.pingcap.com/tidb/v8.3/tidb-binlog-overview) is removed. This variable indicates whether to write changes to TiDB Binlog or not, and is deleted starting from v8.4.0. |
-| [`tidb_enable_global_index`](/system-variables.md#tidb_enable_global_index-new-in-v760) | Deprecated | In v8.4.0, this variable is deprecated. Its value will be fixed to the default value `ON`, that is, [global index](/partitioned-table.md#global-indexes) is enabled by default. You only need to add the keyword `GLOBAL` to the corresponding column when executing `CREATE TABLE` or `ALTER TABLE` to create a global index. |
+| [`tidb_enable_global_index`](/system-variables.md#tidb_enable_global_index-new-in-v760) | Deprecated | In v8.4.0, this variable is deprecated. Its value will be fixed to the default value `ON`, that is, [global index](/global-indexes.md) is enabled by default. You only need to add the keyword `GLOBAL` to the corresponding column when executing `CREATE TABLE` or `ALTER TABLE` to create a global index. |
 | [`tidb_enable_list_partition`](/system-variables.md#tidb_enable_list_partition-new-in-v50) | Deprecated | In v8.4.0, this variable is deprecated. Its value will be fixed to the default value `ON`, that is, [list partitioning](/partitioned-table.md#list-partitioning) is enabled by default. |
 | [`tidb_enable_table_partition`](/system-variables.md#tidb_enable_table_partition) | Deprecated | In v8.4.0, this variable is deprecated. Its value will be fixed to the default value `ON`, that is, [table partitioning](/partitioned-table.md) is enabled by default. |
 | [`tidb_analyze_partition_concurrency`](/system-variables.md#tidb_analyze_partition_concurrency) | Modified | Changes the value range from `[1, 18446744073709551615]` to `[1, 128]`. |

releases/release-8.5.0.md

@@ -51,7 +51,7 @@ Compared with the previous LTS 8.1.0, 8.5.0 includes new features, improvements,
     <td>Instance-level plan cache allows all sessions within the same TiDB instance to share the plan cache. Compared with session-level plan cache, this feature reduces SQL compilation time by caching more execution plans in memory, decreasing overall SQL execution time. It improves OLTP performance and throughput while providing better control over memory usage and enhancing database stability.</td>
   </tr>
   <tr>
-    <td><a href="https://docs.pingcap.com/tidb/v8.5/partitioned-table#global-indexes">Global indexes for partitioned tables</a> (GA in v8.4.0)</td>
+    <td><a href="https://docs.pingcap.com/tidb/v8.5/global-indexes">Global indexes for partitioned tables</a> (GA in v8.4.0)</td>
     <td>Global indexes can effectively improve the efficiency of retrieving non-partitioned columns, and remove the restriction that a unique key must contain the partition key. This feature extends the usage scenarios of TiDB partitioned tables, improves the performance of partitioned tables, and reduces resource consumption in certain query scenarios.</td>
   </tr>
   <tr>

sql-statements/sql-statement-add-column.md

@@ -89,7 +89,7 @@ mysql> SELECT * FROM t1;
 * Adding a new column and setting it to the `PRIMARY KEY` is not supported.
 * Adding a new column and setting it to `AUTO_INCREMENT` is not supported.
 * There are limitations on adding generated columns, refer to: [generated column limitations](/generated-columns.md#limitations).
-* Setting a [global index](/partitioned-table.md#global-indexes) by specifying `PRIMARY KEY` or `UNIQUE INDEX` as `GLOBAL` when you add a new column is a TiDB extension for [partitioned tables](/partitioned-table.md) and is not compatible with MySQL.
+* Setting a [global index](/global-indexes.md) by specifying `PRIMARY KEY` or `UNIQUE INDEX` as `GLOBAL` when you add a new column is a TiDB extension for [partitioned tables](/partitioned-table.md) and is not compatible with MySQL.
 
 ## See also
 

sql-statements/sql-statement-add-index.md

@@ -105,7 +105,7 @@ mysql> EXPLAIN SELECT * FROM t1 WHERE c1 = 3;
 
 * Descending indexes are not supported (similar to MySQL 5.7).
 * Adding the primary key of the `CLUSTERED` type to a table is not supported. For more details about the primary key of the `CLUSTERED` type, refer to [clustered index](/clustered-indexes.md).
-* Setting a `PRIMARY KEY` or `UNIQUE INDEX` as a [global index](/partitioned-table.md#global-indexes) with the `GLOBAL` index option is a TiDB extension for [partitioned tables](/partitioned-table.md) and is not compatible with MySQL.
+* Setting a `PRIMARY KEY` or `UNIQUE INDEX` as a [global index](/global-indexes.md) with the `GLOBAL` index option is a TiDB extension for [partitioned tables](/partitioned-table.md) and is not compatible with MySQL.
 
 ## See also