0.4/2017-11-09--transaction_participants_url_length.xml: fix "max key length is 767 bytes" error from MySQL.

Correction for cee66fd commit.

Author: php-coder

src/main/resources/liquibase/version/0.4/2017-11-09--transaction_participants_url_length.xml

@@ -5,6 +5,26 @@
 		xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog
 		http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-3.0.xsd">
 
+	<changeSet id="modify-transaction_participants-url-charset" author="php-coder" context="scheme" dbms="mysql">
+		<!--
+			Fix for "liquibase.exception.DatabaseException:
+			Specified key was too long; max key length is 767 bytes
+			[Failed SQL: ALTER TABLE mystamps.transaction_participants MODIFY url VARCHAR(285)]".
+			See also: https://stackoverflow.com/questions/1814532/1071-specified-key-was-too-long-max-key-length-is-767-bytes
+		-->
+		<comment>
+			Change character set from utf8 to ascii for a URL field to be able to have a unique
+			constraint on a field that has length greater than 255 characters.
+		</comment>
+		
+		<sql>
+			  ALTER TABLE transaction_participants
+			       MODIFY url VARCHAR(285)
+			CHARACTER SET ascii
+		</sql>
+	
+	</changeSet>
+	
 	<changeSet id="modify-transaction_participants-url-field" author="php-coder" context="scheme">
 		<modifyDataType tableName="transaction_participants" columnName="url" newDataType="VARCHAR(285)" />
 	</changeSet>