ebnf show charset (#17035) (#17146)

sql-statements/sql-statement-show-character-set.md

@@ -9,18 +9,22 @@ This statement provides a static list of available character sets in TiDB. The o
 
 ## Synopsis
 
-**ShowCharsetStmt:**
+```ebnf+diagram
+ShowCharsetStmt ::=
+    "SHOW" ( ("CHARACTER" | "CHAR") "SET" | "CHARSET" ) ShowLikeOrWhere?
 
-![ShowCharsetStmt](/media/sqlgram/ShowCharsetStmt.png)
-
-**CharsetKw:**
-
-![CharsetKw](/media/sqlgram/CharsetKw.png)
+ShowLikeOrWhere ::=
+    "LIKE" SimpleExpr
+|   "WHERE" Expression
+```
 
 ## Examples
 
 ```sql
-mysql> SHOW CHARACTER SET;
+SHOW CHARACTER SET;
+```
+
+```
 +---------+---------------+-------------------+--------+
 | Charset | Description   | Default collation | Maxlen |
 +---------+---------------+-------------------+--------+
@@ -33,6 +37,34 @@ mysql> SHOW CHARACTER SET;
 5 rows in set (0.00 sec)
 ```
 
+```sql
+SHOW CHARACTER SET LIKE 'utf8%';
+```
+
+```
++---------+---------------+-------------------+--------+
+| Charset | Description   | Default collation | Maxlen |
++---------+---------------+-------------------+--------+
+| utf8    | UTF-8 Unicode | utf8_bin          |      3 |
+| utf8mb4 | UTF-8 Unicode | utf8mb4_bin       |      4 |
++---------+---------------+-------------------+--------+
+2 rows in set (0.00 sec)
+```
+
+```sql
+SHOW CHARACTER SET WHERE Description='UTF-8 Unicode';
+```
+
+```
++---------+---------------+-------------------+--------+
+| Charset | Description   | Default collation | Maxlen |
++---------+---------------+-------------------+--------+
+| utf8    | UTF-8 Unicode | utf8_bin          |      3 |
+| utf8mb4 | UTF-8 Unicode | utf8mb4_bin       |      4 |
++---------+---------------+-------------------+--------+
+2 rows in set (0.00 sec)
+```
+
 ## MySQL compatibility
 
 The usage of `SHOW CHARACTER SET` statement in TiDB is fully compatible with MySQL. However, charsets in TiDB might have different default collations compared with MySQL. For details, refer to [Compatibility with MySQL](/mysql-compatibility.md). If you find any compatibility differences, [report a bug](https://docs.pingcap.com/tidb/stable/support).