From 8017af5eb1ac3eb6552ccedef50b302457f35dda Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Dani=C3=ABl=20van=20Eeden?= Date: Wed, 26 May 2021 11:49:43 +0200 Subject: [PATCH] Add documentation for TiDB specific SQL functions --- TOC.md | 1 + .../information-functions.md | 1 - functions-and-operators/tidb-functions.md | 190 ++++++++++++++++++ 3 files changed, 191 insertions(+), 1 deletion(-) create mode 100644 functions-and-operators/tidb-functions.md diff --git a/TOC.md b/TOC.md index 79dc4f1e59825..ca3c3b49d7a22 100644 --- a/TOC.md +++ b/TOC.md @@ -396,6 +396,7 @@ + [Precision Math](/functions-and-operators/precision-math.md) + [Set Operations](/functions-and-operators/set-operators.md) + [List of Expressions for Pushdown](/functions-and-operators/expressions-pushed-down.md) + + [TiDB specific Functions](/functions-and-operators/tidb-functions.md) + [Clustered Indexes](/clustered-indexes.md) + [Constraints](/constraints.md) + [Generated Columns](/generated-columns.md) diff --git a/functions-and-operators/information-functions.md b/functions-and-operators/information-functions.md index 98877381ab3a8..575518326a0ec 100644 --- a/functions-and-operators/information-functions.md +++ b/functions-and-operators/information-functions.md @@ -24,7 +24,6 @@ TiDB supports most of the [information functions](https://dev.mysql.com/doc/refm | [`SYSTEM_USER()`](https://dev.mysql.com/doc/refman/5.7/en/information-functions.html#function_system-user) | Synonym for `USER()` | | [`USER()`](https://dev.mysql.com/doc/refman/5.7/en/information-functions.html#function_user) | Return the user name and host name provided by the client | | [`VERSION()`](https://dev.mysql.com/doc/refman/5.7/en/information-functions.html#function_version) | Return a string that indicates the MySQL server version | -| `TIDB_VERSION()` | Return a string that indicates the TiDB server version | ## Unsupported functions diff --git a/functions-and-operators/tidb-functions.md b/functions-and-operators/tidb-functions.md new file mode 100644 index 0000000000000..bed77a3893ac2 --- /dev/null +++ b/functions-and-operators/tidb-functions.md @@ -0,0 +1,190 @@ +--- +title: TABLE | TiDB SQL Function Reference +summary: An overview of the usage of TiDB specific functions for the TiDB database. +--- + +# TIDB_BOUNDED_STALENESS + +The `TIDB_BOUNDED_STALENESS` function is an internal function of TiDB. + +# TIDB_DECODE_KEY + +The `TIDB_DECODE_KEY` can be used to decode a TiDB encoded key entry into a JSON structure containing the `_tidb_rowid` and the `table_id`. These encoded keys can be found in some system tables and in logging output. + +## Synopsis + +```ebnf+diagram +TableStmt ::= + "TIDB_DECODE_KEY(" STR ")" +``` + +## Examples + +{{< copyable "sql" >}} + +```sql +SELECT START_KEY, TIDB_DECODE_KEY(START_KEY) FROM information_schema.tikv_region_status WHERE table_name='t1' AND REGION_ID=2\G +``` + +```sql +*************************** 1. row *************************** + START_KEY: 7480000000000000FF3B5F728000000000FF1DE3F10000000000FA +TIDB_DECODE_KEY(START_KEY): {"_tidb_rowid":1958897,"table_id":"59"} +1 row in set (0.00 sec) +``` + +## MySQL compatibility + +The `TIDB_DECODE_KEY` function is TiDB specific and is not compatible with MySQL. + +# TIDB_DECODE_PLAN + +The `TIDB_DECODE_PLAN` can be used to decode a TiDB execution plan. These plans can be found in the slow query log. + +## Synopsis + +```ebnf+diagram +TableStmt ::= + "TIDB_DECODE_PLAN(" STR ")" +``` + +## Examples + +{{< copyable "sql" >}} + +```sql +SELECT tidb_decode_plan('8QIYMAkzMV83CQEH8E85LjA0CWRhdGE6U2VsZWN0aW9uXzYJOTYwCXRpbWU6NzEzLjHCtXMsIGxvb3BzOjIsIGNvcF90YXNrOiB7bnVtOiAxLCBtYXg6IDU2OC41wgErRHByb2Nfa2V5czogMCwgcnBjXxEpAQwFWBAgNTQ5LglZyGNvcHJfY2FjaGVfaGl0X3JhdGlvOiAwLjAwfQkzLjk5IEtCCU4vQQoxCTFfNgkxXzAJMwm2SGx0KHRlc3QudC5hLCAxMDAwMCkNuQRrdgmiAHsFbBQzMTMuOMIBmQnEDDk2MH0BUgEEGAoyCTQzXzUFVwX1oGFibGU6dCwga2VlcCBvcmRlcjpmYWxzZSwgc3RhdHM6cHNldWRvCTk2ISE2aAAIMTUzXmYA')\G +``` + +```sql +*************************** 1. row *************************** + tidb_decode_plan('8QIYMAkzMV83CQEH8E85LjA0CWRhdGE6U2VsZWN0aW9uXzYJOTYwCXRpbWU6NzEzLjHCtXMsIGxvb3BzOjIsIGNvcF90YXNrOiB7bnVtOiAxLCBtYXg6IDU2OC41wgErRHByb2Nfa2V5czogMCwgcnBjXxEpAQwFWBAgNTQ5LglZyGNvcHJfY2FjaGVfaGl0X3JhdGlvOiAwLjAwfQkzLjk5IEtCCU4vQQoxCTFfNgkxXz: id task estRows operator info actRows execution info memory disk + TableReader_7 root 319.04 data:Selection_6 960 time:713.1µs, loops:2, cop_task: {num: 1, max: 568.5µs, proc_keys: 0, rpc_num: 1, rpc_time: 549.1µs, copr_cache_hit_ratio: 0.00} 3.99 KB N/A + └─Selection_6 cop[tikv] 319.04 lt(test.t.a, 10000) 960 tikv_task:{time:313.8µs, loops:960} N/A N/A + └─TableFullScan_5 cop[tikv] 960 table:t, keep order:false, stats:pseudo 960 tikv_task:{time:153µs, loops:960} N/A N/A +``` + +## MySQL compatibility + +The `TIDB_DECODE_PLAN` function is TiDB specific and is not compatible with MySQL. + +# TIDB_IS_DDL_OWNER + +The `TIDB_IS_DDL_OWNER` function can be used to check if the TiDB instance you are connected to is the one that is the DDL Owner. The DDL Owner is the TiDB instance that is tasked with executing DDL on behalf of all other nodes in the cluster. + +## Synopsis + +```ebnf+diagram +TableStmt ::= + "TIDB_IS_DDL_OWNER())" +``` + +## Examples + +{{< copyable "sql" >}} + +```sql +SELECT tidb_is_ddl_owner(); +``` + +```sql ++---------------------+ +| tidb_is_ddl_owner() | ++---------------------+ +| 1 | ++---------------------+ +1 row in set (0.00 sec) +``` + +## MySQL compatibility + +The `TIDB_IS_DDL_OWNER` function is TiDB specific and is not compatible with MySQL. + +## See also + +- [ADMIN SHOW DDL](/sql-statements/sql-statement-admin-show-ddl.md) +- [ADMIN CANCEL DDL](/sql-statements/sql-statement-cancel-ddl.md) + +# TIDB_PARSE_TSO + +The `TIDB_PARSE_TSO` function can be used to extract the physical timestamp from a TiDB TSO timestamp. + +TSO stands for Time Stamp Oracle and is a monotonically increaseasing timestamp given out by PD (placement driver) for every transaction. + +A TSO is a number that consists of two parts: + +- A physical timestamp +- A logical counter + +## Synopsis + +```ebnf+diagram +TableStmt ::= + "TIDB_PARSE_TSO(" NUM ")" +``` + +## Examples + +{{< copyable "sql" >}} + +```sql +BEGIN; +SELECT TIDB_PARSE_TSO(@@tidb_current_ts); +ROLLBACK; +``` + +```sql ++-----------------------------------+ +| TIDB_PARSE_TSO(@@tidb_current_ts) | ++-----------------------------------+ +| 2021-05-26 11:33:37.776000 | ++-----------------------------------+ +1 row in set (0.0012 sec) +``` + +Here `TIDB_PARSE_TSO` is used to extract the physical timestamp from the timestamp number that is available in the `tidb_current_ts` session variable. As timestamps are given out per transactions this is running in an transaction. + +## MySQL compatibility + +The `TIDB_PARSE_TSO` function is TiDB specific and is not compatible with MySQL. + +## See also + +- [tidb_current_ts](/system-variables.md#tidb_current_ts) + +# TIDB_VERSION + +The `TIDB_VERSION` function can be used to get version and buil details of the TiDB server you are connected to. This can be used when reporting issues on GitHub. + +## Synopsis + +```ebnf+diagram +TableStmt ::= + "TIDB_VERSION()" +``` + +## Examples + +{{< copyable "sql" >}} + +```sql +SELECT TIDB_VERSION()\G +``` + +```sql +*************************** 1. row *************************** +TIDB_VERSION(): Release Version: v5.1.0-alpha-13-gd5e0ed0aa-dirty +Edition: Community +Git Commit Hash: d5e0ed0aaed72d2f2dfe24e9deec31cb6cb5fdf0 +Git Branch: master +UTC Build Time: 2021-05-24 14:39:20 +GoVersion: go1.13 +Race Enabled: false +TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306 +Check Table Before Drop: false +1 row in set (0.00 sec) +``` + +## MySQL compatibility + +The `TIDB_VERSION` function is TiDB specific and is not compatible with MySQL. Requesting version information with `VERSION` can be used if MySQL compatibility is required, but this doesn't contain build details. \ No newline at end of file