wayneguow commented on code in PR #49564:
URL: https://github.com/apache/spark/pull/49564#discussion_r1929496676
##########
sql/core/src/main/scala/org/apache/spark/sql/jdbc/MySQLDialect.scala:
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@@ -406,7 +406,7 @@ private case class MySQLDialect() extends JdbcDialect with
SQLConfHelper with No
}
options.prepareQuery +
- s"SELECT $columnList FROM ${options.tableOrQuery} $tableSampleClause" +
+ s"SELECT ${options.hint}$columnList FROM ${options.tableOrQuery}
$tableSampleClause" +
Review Comment:
> is there an spec to say that the "HINT" could only appear in the SELECT
clause?
@pan3793 Currently `hints` are not a standard feature defined in the
`ANSI/ISO` SQL standards, so there is no an spec for `hints`.
However, in current mainstream DBMS and Spark(mentioned by @dongjoon-hyun) ,
the definition of the `hints` feature is basically required to follow keywords
such as `SELECT`:
- Oracle:
https://docs.oracle.com/en/database/oracle/oracle-database/23/sqlrf/Comments.html
<img width="661" alt="image"
src="https://github.com/user-attachments/assets/fdf22e48-bc56-4347-995d-2b175ec74020";
/>
- MySQL: https://dev.mysql.com/doc/refman/8.4/en/optimizer-hints.html
<img width="932" alt="image"
src="https://github.com/user-attachments/assets/6a8ed91c-991a-414a-8896-cf403027ff0b";
/>
-
Databricks：https://docs.databricks.com/en/sql/language-manual/sql-ref-syntax-qry-select.html
<img width="710" alt="image"
src="https://github.com/user-attachments/assets/9bd21b2e-5c9b-471f-b552-6bd2352ac1a8";
/>
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