Added optional AS alias to docs

h2/src/docsrc/help/help.csv

@@ -123,15 +123,15 @@ MERGE INTO TEST KEY(ID) VALUES(2, 'World')
 "
 
 "Commands (DML)","MERGE USING","
-MERGE INTO targetTableName [AS targetAlias] 
-USING { ( select ) | sourceTableName }[ AS sourceAlias ]
+MERGE INTO targetTableName [ [AS] targetAlias] 
+USING { ( select ) | sourceTableName }[ [AS] sourceAlias ]
 ON ( expression ) 
 [ WHEN MATCHED THEN [ update ] [ delete] ]
 [ WHEN NOT MATCHED THEN insert  ]
 ","
 Updates or deletes existing rows, and insert rows that don't exist. The ON clause 
-specifies the key column expression and must be specified. If more than one row is updated 
-per input row, an exception is thrown. 
+specifies the matching column expression and must be specified. If more than one row 
+is updated per input row, an exception is thrown. 
 If the source data contains duplicate rows (specifically those columns used in the 
 row matching ON clause), then an exception is thrown to prevent two updates applying 
 to the same target row. The embedded update, delete or insert statements can not re-specify