[
https://issues.apache.org/jira/browse/CALCITE-6798?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17916878#comment-17916878
]
ZheHu commented on CALCITE-6798:
--------------------------------
Thanks for noticing this [~suibianwanwan33] [~julianhyde]. In
RelFieldCollation, the default null direction for ASCENDING is
NullDirection.LAST, which I think this is not dialect related.
{code:java}
@Test void testMySqlSelectQueryWithAscWithoutNullsDirection() {
final String query = "select \"product_id\" from \"product\"\n"
+ "order by \"product_id\" asc";
final String expected = "SELECT `product_id`\n"
+ "FROM `foodmart`.`product`\n"
+ "ORDER BY `product_id` IS NULL, `product_id`";
sql(query).dialect(MysqlSqlDialect.DEFAULT).ok(expected);
}
{code}
has the following RelNode:
{code:java}
LogicalSort(sort0=[$0], dir0=[ASC])
LogicalProject(product_id=[$1])
JdbcTableScan(table=[[foodmart, product]])
{code}
When converting it with MySQL dialect, there is actually an implicit "NULLS
LAST" for "product_id" field (because of under Calcite syntax, and this is
where I get lost), so the expected sql is right.
I agree it's not a bug.
> Null direction emulation in MySQL and Hive is incorrect when null direction
> is not specified
> --------------------------------------------------------------------------------------------
>
> Key: CALCITE-6798
> URL: https://issues.apache.org/jira/browse/CALCITE-6798
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.38.0
> Reporter: ZheHu
> Assignee: ZheHu
> Priority: Major
>
> The following test passes in {{RelToSqlConverterTest}}.
> {code:java}
> @Test void testMySqlSelectQueryWithAscWithoutNullsDirection() {
> final String query = "select \"product_id\" from \"product\"\n"
> + "order by \"product_id\" asc";
> final String expected = "SELECT `product_id`\n"
> + "FROM `foodmart`.`product`\n"
> + "ORDER BY `product_id` IS NULL, `product_id`";
> sql(query).dialect(MysqlSqlDialect.DEFAULT).ok(expected);
> }
> {code}
> According to
> [mysql-doc|https://dev.mysql.com/doc/refman/8.0/en/working-with-null.html],
> NULL values are presented first if you do ORDER BY ... ASC and last if you do
> ORDER BY ... DESC, and [default
> |https://dev.mysql.com/doc/refman/8.0/en/sorting-rows.html]sort order is
> ascending. Hence, the query after dialect convert will result in NULL values
> presented last if you do ORDER BY ... ASC and first if you do ORDER BY ...
> DESC.
> HiveSqlDialect has the same problem with MySQL.
> PrestoSqlDialect has NullCollation.LAST strategy, the following query with
> DESC sort after dialect will make NULL values presented first (asc works
> fine).
> {code:java}
> @Test void testPrestoSelectQueryWithDescWithoutNullsDirection() {
> final String query = "select \"product_id\" from \"product\"\n"
> + "order by \"product_id\" desc";
> final String expected = "SELECT `product_id`\n"
> + "FROM `foodmart`.`product`\n"
> + "ORDER BY `product_id` IS NULL DESC, `product_id` DESC";
> sql(query).dialect(PrestoSqlDialect.DEFAULT).ok(expected);
> }
> {code}
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
