support charset clause

sharding-jdbc-ddl-parser/src/main/resources/io/shardingsphere/parser/antlr/MySQLDQL.g4

@@ -185,6 +185,7 @@ characterAndCollate:
 	
 characterSet:
 	((CHARACTER | CHAR) SET charsetName)
+	|CHARSET EQ_OR_ASSIGN? charsetName
 	;
 	
 collateClause:
@@ -203,6 +204,7 @@ characterAndCollateWithEqual:
 		
 characterSetWithEqual:
 	((CHARACTER | CHAR) SET EQ_OR_ASSIGN? charsetName)
+	|CHARSET EQ_OR_ASSIGN? charsetName
 	;
 			
 collateClauseWithEqual:

sharding-jdbc-ddl-parser/src/main/resources/io/shardingsphere/parser/antlr/MySQLKeyword.g4

@@ -9,6 +9,7 @@ ALGORITHM: A L G O R I T H M;
 CHANGE: C H A N G E;
 DISCARD: D I S C A R D;
 CHARACTER: C H A R A C T E R;
+CHARSET: C H A R S E T;
 COLLATE: C O L L A T E;
 CONVERT: C O N V E R T;
 SHARED: S H A R E D;