sql statement: add document for SET ROLE (#2825)

TOC.md

@@ -213,6 +213,7 @@
       - [`SELECT`](/sql-statements/sql-statement-select.md)
       - [`SET [NAMES|CHARACTER SET]`](/sql-statements/sql-statement-set-names.md)
       - [`SET PASSWORD`](/sql-statements/sql-statement-set-password.md)
+      + [`SET ROLE`](/sql-statements/sql-statement-set-role.md)
       - [`SET TRANSACTION`](/sql-statements/sql-statement-set-transaction.md)
       - [`SET [GLOBAL|SESSION] <variable>`](/sql-statements/sql-statement-set-variable.md)
       - [`SHOW ANALYZE STATUS`](/sql-statements/sql-statement-show-analyze-status.md)

sql-statements/sql-statement-set-role.md

@@ -0,0 +1,113 @@
+---
+title: SET ROLE | TiDB SQL Statement Reference
+summary: An overview of the usage of SET ROLE for the TiDB database.
+category: reference
+---
+
+# SET ROLE
+
+The `SET ROLE` statement is used to enable roles in the current session. After enabling roles, users can use the privileges of the role(s).  
+
+## Synopsis
+
+**SetRoleStmt:**
+
+![SetRoleStmt](/media/sqlgram/SetRoleStmt.png)
+
+**SetRoleOpt:**
+
+![SetRoleOpt](/media/sqlgram/SetRoleOpt.png)
+
+**SetDefaultRoleOpt:**
+
+![SetDefaultRoleOpt](/media/sqlgram/SetDefaultRoleOpt.png)
+
+## Examples
+
+Create a user `'u1'@'%'` and three roles: `'r1'@'%'`, `'r2'@'%'` and `'r3'@'%'`.
+Grant these roles to `'u1'@'%'` and set `'r1'@'%'` as the defualt role of `'u1'@'%'`.
+
+{{< copyable "sql" >}}
+
+```sql
+CREATE USER 'u1'@'%';
+CREATE ROLE 'r1', 'r2', 'r3';
+GRANT 'r1', 'r2', 'r3' TO 'u1'@'%'; 
+SET DEFAULT ROLE 'r1' TO 'u1'@'%'; 
+```
+
+Log in as `'u1'@'%'` and execute the following `SET ROLE` statement to enable all roles.
+
+{{< copyable "sql" >}}
+
+```sql
+SET ROLE ALL;
+SELECT CURRENT_ROLE();
+```
+
+```
++----------------------------+
+| CURRENT_ROLE()             |
++----------------------------+
+| `r1`@`%`,`r2`@`%`,`r3`@`%` |
++----------------------------+
+1 row in set (0.000 sec)
+```
+
+Execute the following `SET ROLE` statement to enable `'r2'` and `'r3'`.
+
+{{< copyable "sql" >}}
+
+```sql
+SET ROLE 'r2', 'r3';
+SELECT CURRENT_ROLE();
+```
+
+```
++-------------------+
+| CURRENT_ROLE()    |
++-------------------+
+| `r2`@`%`,`r3`@`%` |
++-------------------+
+1 row in set (0.000 sec)
+```
+
+Execute the following `SET ROLE` statement to enable the default role(s).
+
+{{< copyable "sql" >}}
+
+```sql
+SET ROLE DEFAULT;
+SELECT CURRENT_ROLE();
+```
+
+```
++----------------+
+| CURRENT_ROLE() |
++----------------+
+| `r1`@`%`       |
++----------------+
+1 row in set (0.000 sec)
+```
+
+Execute the following `SET ROLE` statement to cancel all enabled role(s).
+
+{{< copyable "sql" >}}
+
+```sql
+SET ROLE NONE;
+SELECT CURRENT_ROLE();
+```
+
+```
++----------------+
+| CURRENT_ROLE() |
++----------------+
+|                |
++----------------+
+1 row in set (0.000 sec)
+```
+
+## See also
+
+* [Role-Based Access Control](/role-based-access-control.md)