functions: Add TIDB_MVCC_INFO and TIDB_ENCODE_INDEX_KEY

functions-and-operators/tidb-functions.md

@@ -18,8 +18,10 @@ The following functions are TiDB extensions, and are not present in MySQL:
 | [`TIDB_DECODE_KEY()`](#tidb_decode_key) | Decodes a TiDB-encoded key entry into a JSON structure containing `_tidb_rowid` and `table_id`. These encoded keys can be found in some system tables and logging outputs. |
 | [`TIDB_DECODE_PLAN()`](#tidb_decode_plan) | Decodes a TiDB execution plan. |
 | [`TIDB_DECODE_SQL_DIGESTS()`](#tidb_decode_sql_digests) | Queries the normalized SQL statements (a form without formats and arguments) corresponding to a set of SQL digests in the cluster. |
+| [`TIDB_ENCODE_INDEX_KEY()`](#tidb_encode_index_key) | Encodes an index key. |
 | [`TIDB_ENCODE_SQL_DIGEST()`](#tidb_encode_sql_digest) | Gets a digest for a query string. |
 | [`TIDB_IS_DDL_OWNER()`](#tidb_is_ddl_owner) | Checks whether or not the TiDB instance you are connected to is the DDL Owner. The DDL Owner is the TiDB instance that is tasked with executing DDL statements on behalf of all other nodes in the cluster. |
+| [`TIDB_MVCC_INFO()`](#tidb_mvcc_info) | Returns MVCC info about a key. |
 | [`TIDB_PARSE_TSO()`](#tidb_parse_tso) | Extracts the physical timestamp from a TiDB TSO timestamp. See also: [`tidb_current_ts`](/system-variables.md#tidb_current_ts). |
 | [`TIDB_PARSE_TSO_LOGICAL()`](#tidb_parse_tso_logical) | Extracts the logical timestamp from a TiDB TSO timestamp. |
 | [`TIDB_ROW_CHECKSUM()`](#tidb_row_checksum) | Queries the checksum value of a row. This function can only be used in `SELECT` statements within the FastPlan process. That is, you can query through statements like `SELECT TIDB_ROW_CHECKSUM() FROM t WHERE id = ?` or `SELECT TIDB_ROW_CHECKSUM() FROM t WHERE id IN (?, ?, ...)`. See also: [Data integrity validation for single-row data](/ticdc/ticdc-integrity-check.md). |
@@ -40,9 +42,11 @@ The following functions are TiDB extensions, and are not present in MySQL:
 | [`TIDB_DECODE_KEY()`](#tidb_decode_key) | Decodes a TiDB-encoded key entry into a JSON structure containing `_tidb_rowid` and `table_id`. These encoded keys can be found in some system tables and logging outputs. |
 | [`TIDB_DECODE_PLAN()`](#tidb_decode_plan) | Decodes a TiDB execution plan. |
 | [`TIDB_DECODE_SQL_DIGESTS()`](#tidb_decode_sql_digests) | Queries the normalized SQL statements (a form without formats and arguments) corresponding to a set of SQL digests in the cluster. |
+| [`TIDB_ENCODE_INDEX_KEY()`](#tidb_encode_index_key) | Encodes an index key. |
 | [`TIDB_ENCODE_SQL_DIGEST()`](#tidb_encode_sql_digest) | Gets a digest for a query string. |
 | [`TIDB_IS_DDL_OWNER()`](#tidb_is_ddl_owner) | Checks whether or not the TiDB instance you are connected to is the DDL Owner. The DDL Owner is the TiDB instance that is tasked with executing DDL statements on behalf of all other nodes in the cluster. |
 | [`TIDB_PARSE_TSO()`](#tidb_parse_tso) | Extracts the physical timestamp from a TiDB TSO timestamp. See also: [`tidb_current_ts`](/system-variables.md#tidb_current_ts). |
+| [`TIDB_MVCC_INFO()`](#tidb_mvcc_info) | Returns MVCC info about a key. |
 | [`TIDB_PARSE_TSO_LOGICAL()`](#tidb_parse_tso_logical) | Extracts the logical timestamp from a TiDB TSO timestamp. |
 | [`TIDB_ROW_CHECKSUM()`](#tidb_row_checksum) | Queries the checksum value of a row. This function can only be used in `SELECT` statements within the FastPlan process. That is, you can query through statements like `SELECT TIDB_ROW_CHECKSUM() FROM t WHERE id = ?` or `SELECT TIDB_ROW_CHECKSUM() FROM t WHERE id IN (?, ?, ...)`. See also: [Data integrity validation for single-row data](https://docs.pingcap.com/tidb/stable/ticdc-integrity-check). |
 | [`TIDB_SHARD()`](#tidb_shard) | Creates a shard index to scatter the index hotspot. A shard index is an expression index with a `TIDB_SHARD` function as the prefix.|
@@ -573,4 +577,72 @@ SELECT VITESS_HASH(123);
 | 1155070131015363447 |
 +---------------------+
 1 row in set (0.00 sec)
-```
+```
+
+## TIDB_ENCODE_INDEX_KEY
+
+Encodes an index key.
+
+```sql
+CREATE TABLE t(id int PRIMARY KEY, a int, KEY `idx` (a));
+```
+
+```
+Query OK, 0 rows affected (0.00 sec)
+```
+
+```sql
+INSERT INTO t VALUES(1,1);
+```
+
+```
+Query OK, 1 row affected (0.00 sec)
+```
+
+```sql
+SELECT TIDB_ENCODE_INDEX_KEY('test', 't', 'idx', 1, 1);
+```
+
+```
++----------------------------------------------------------------------------+
+| TIDB_ENCODE_INDEX_KEY('test', 't', 'idx', 1, 1)                            |
++----------------------------------------------------------------------------+
+| 74800000000000007f5f698000000000000001038000000000000001038000000000000001 |
++----------------------------------------------------------------------------+
+1 row in set (0.00 sec)
+```
+
+## TIDB_MVCC_INFO
+
+Returns MVCC info for a key. The `TIDB_ENCODE_INDEX_KEY` function can be used to obtain a key.
+
+```sql
+SELECT JSON_PRETTY(TIDB_MVCC_INFO('74800000000000007f5f698000000000000001038000000000000001038000000000000001')) AS info\G
+```
+
+```
+*************************** 1. row ***************************
+info: [
+  {
+    "key": "74800000000000007f5f698000000000000001038000000000000001038000000000000001",
+    "mvcc": {
+      "info": {
+        "values": [
+          {
+            "start_ts": 454654803134119936,
+            "value": "MA=="
+          }
+        ],
+        "writes": [
+          {
+            "commit_ts": 454654803134119937,
+            "short_value": "MA==",
+            "start_ts": 454654803134119936
+          }
+        ]
+      }
+    }
+  }
+]
+1 row in set (0.00 sec)
+```