sjwiesman commented on a change in pull request #17264:
URL: https://github.com/apache/flink/pull/17264#discussion_r710261987
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File path:
flink-connectors/flink-connector-jdbc/src/main/java/org/apache/flink/connector/jdbc/dialect/JdbcDialect.java
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@@ -83,27 +86,37 @@ default void validate(TableSchema schema) throws
ValidationException {}
}
/**
- * Quotes the identifier. This is used to put quotes around the identifier
in case the column
- * name is a reserved keyword, or in case it contains characters that
require quotes (e.g.
- * space). Default using double quotes {@code "} to quote.
+ * Quotes the identifier.
+ *
+ * <p>Used to put quotes around the identifier if the column name is a
reserved keyword or
+ * contains characters requiring quotes (e.g., space). Default using
double quotes {@code "} to
+ * quote.
+ *
+ * @return the quoted identifier.
*/
default String quoteIdentifier(String identifier) {
return "\"" + identifier + "\"";
}
/**
- * Get dialect upsert statement, the database has its own upsert syntax,
such as Mysql using
- * DUPLICATE KEY UPDATE, and PostgreSQL using ON CONFLICT... DO UPDATE
SET..
+ * Constructs the dialects upsert statement if supported; such as MySQL's
{@code DUPLICATE KEY
+ * UPDATE}, or PostgreSQLs {@code ON CONFLICT... DO UPDATE SET..}.
+ *
+ * <p>If the dialect does not support native upsert statements, the writer
will fallback to
+ * {@code SELECT} + {@code Update}/{@code INSERT} which may have poor
performance.
*
- * @return None if dialect does not support upsert statement, the writer
will degrade to the use
- * of select + update/insert, this performance is poor.
+ * @return The upsert statement if supported, otherwise None.
*/
default Optional<String> getUpsertStatement(
String tableName, String[] fieldNames, String[] uniqueKeyFields) {
Review comment:
agreed
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