[GitHub] [flink] fsk119 commented on a diff in pull request #19741: [FLINK-27794][connector/jdbc] The primary key obtained from MySQL is incorrect by using MysqlCatalog

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fsk119 commented on code in PR #19741:
URL: https://github.com/apache/flink/pull/19741#discussion_r884449039


##########
flink-connectors/flink-connector-jdbc/src/main/java/org/apache/flink/connector/jdbc/catalog/AbstractJdbcCatalog.java:
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@@ -149,7 +149,7 @@ protected Optional<UniqueConstraint> getPrimaryKey(
         // According to the Javadoc of java.sql.DatabaseMetaData#getPrimaryKeys,
         // the returned primary key columns are ordered by COLUMN_NAME, not by KEY_SEQ.
         // We need to sort them based on the KEY_SEQ value.
-        ResultSet rs = metaData.getPrimaryKeys(null, schema, table);
+        ResultSet rs = metaData.getPrimaryKeys(schema, schema, table);

Review Comment:
   In the SQL world, catalog and schema are different things.  We can not mix them up. You can refer to the doc to see the difference[1]. In the MySql world, they has the same meaning[2]. 
   But in the PostgreSQL, catalog has many schemas[3].
   
   
   Therefore, I think you should do as the schema and let the specified catalog to determine the catalog of the specified table.
   
   
   
   [1] https://stackoverflow.com/questions/7022755/whats-the-difference-between-a-catalog-and-a-schema-in-a-relational-database 
   [2] https://dev.mysql.com/doc/connector-odbc/en/connector-odbc-usagenotes-functionality-catalog-schema.html
   [3] https://stackoverflow.com/questions/48312675/how-can-i-show-the-catalogs-and-schemas-in-postgresql



##########
flink-connectors/flink-connector-jdbc/src/main/java/org/apache/flink/connector/jdbc/catalog/MySqlCatalog.java:
##########
@@ -152,7 +152,7 @@ protected String getTableName(ObjectPath tablePath) {
 
     @Override
     protected String getSchemaName(ObjectPath tablePath) {
-        return null;
+        return tablePath.getDatabaseName();

Review Comment:
   Please add some comments to tell others that the schema is equal to the database[1].
   
   [1] https://dev.mysql.com/doc/connector-odbc/en/connector-odbc-usagenotes-functionality-catalog-schema.html



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