[FLINK-38641][cdc/mysql] Unquote double quotes from default values on MySQL (#4171)

Author: beryllw

flink-cdc-connect/flink-cdc-source-connectors/flink-connector-mysql-cdc/src/main/java/io/debezium/connector/mysql/antlr/listener/DefaultValueParserListener.java

@@ -95,7 +95,9 @@ public void exitDefaultValue(boolean skipIfUnknownOptional) {
     }
 
     private String unquote(String stringLiteral) {
-        if (stringLiteral != null && stringLiteral.startsWith("'") && stringLiteral.endsWith("'")) {
+        if (stringLiteral != null
+                && ((stringLiteral.startsWith("'") && stringLiteral.endsWith("'"))
+                        || (stringLiteral.startsWith("\"") && stringLiteral.endsWith("\"")))) {
             return stringLiteral.substring(1, stringLiteral.length() - 1);
         }
         return stringLiteral;

flink-cdc-connect/flink-cdc-source-connectors/flink-connector-mysql-cdc/src/test/java/org/apache/flink/cdc/connectors/mysql/table/MySqlConnectorITCase.java

@@ -1514,7 +1514,7 @@ void testDdlWithDefaultStringValue() throws Exception {
                             + "     double_c DOUBLE DEFAULT ' 25',\n"
                             + "     double_un_c DOUBLE UNSIGNED DEFAULT ' 26',\n"
                             + "     double_un_z_c DOUBLE UNSIGNED ZEROFILL DEFAULT ' 27',\n"
-                            + "     tiny_un_c TINYINT UNSIGNED DEFAULT ' 28 '"
+                            + "     tiny_un_c TINYINT UNSIGNED DEFAULT \" 28 \""
                             + " );");
         }
         actualRows.addAll(fetchRows(iterator, expected.length - 2));