panbingkun commented on code in PR #37031:
URL: https://github.com/apache/spark/pull/37031#discussion_r912439421
##########
sql/core/src/main/scala/org/apache/spark/sql/jdbc/MySQLDialect.scala:
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@@ -217,7 +219,7 @@ private case object MySQLDialect extends JdbcDialect with
SQLConfHelper {
// The only property we are building here is `COMMENT` because
it's the only one
// we can get from `SHOW INDEXES`.
val properties = new util.Properties();
- if (indexComment.nonEmpty) properties.put("COMMENT", indexComment)
Review Comment:
> Yes, you are right! I investigated it carefully.
> INDEX_COMMENT nullability is NO, the default value is empty String.
mysql> desc INFORMATION_SCHEMA.STATISTICS;
+---------------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------------+---------------+------+-----+---------+-------+
| TABLE_CATALOG | varchar(512) | NO | | | |
| TABLE_SCHEMA | varchar(64) | NO | | | |
| TABLE_NAME | varchar(64) | NO | | | |
| NON_UNIQUE | bigint(1) | NO | | 0 | |
| INDEX_SCHEMA | varchar(64) | NO | | | |
| INDEX_NAME | varchar(64) | NO | | | |
| SEQ_IN_INDEX | bigint(2) | NO | | 0 | |
| COLUMN_NAME | varchar(64) | NO | | | |
| COLLATION | varchar(1) | YES | | NULL | |
| CARDINALITY | bigint(21) | YES | | NULL | |
| SUB_PART | bigint(3) | YES | | NULL | |
| PACKED | varchar(10) | YES | | NULL | |
| NULLABLE | varchar(3) | NO | | | |
| INDEX_TYPE | varchar(16) | NO | | | |
| COMMENT | varchar(16) | YES | | NULL | |
**| INDEX_COMMENT | varchar(1024) | NO | | | |**
+---------------+---------------+------+-----+---------+-------+
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