Github user HyukjinKwon commented on a diff in the pull request:
https://github.com/apache/spark/pull/8391#discussion_r37830657
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/jdbc/JDBCRDD.scala
---
@@ -275,6 +275,7 @@ private[sql] class JDBCRDD(
*/
private def compileFilter(f: Filter): String = f match {
case EqualTo(attr, value) => s"$attr = ${compileValue(value)}"
+ case EqualNullSafe(attr, value) => s"$attr <=> ${compileValue(value)}"
--- End diff --
I thought the comparison operator is official and a standard one (because
both I am used to MySQL and thought Spark and Hive uses Standard SQL Syntax).
However, it looks like it is a MySQL dialect.
In details,
Firstly, I looked through several documents.
I assume there are several standard documentations as mentioned in the
`Where can I get a copy of the SQL standards?`
https://wiki.postgresql.org/wiki/Developer_FAQ#Where_can_I_get_a_copy_of_the_SQL_standards.3F).
(SQL-92 http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt
SQL:1999
http://web.cs.ualberta.ca/~yuan/courses/db_readings/ansi-iso-9075-2-1999.pdf
SQL:2003 http://www.wiscorp.com/sql_2003_standard.zip
SQL:201x (preliminary) http://www.wiscorp.com/sql20nn.zip)
Though I can guarantee, It looks null-safe equality comparison is not the
standard one. It seems there are no mentions about this.
Secondly, I got a list of the top 10 databases here
(http://www.improgrammer.net/top-10-databases-should-learn-2015/)
and reviewed if there is a such operation or not.
1. Oracle - not support (http://docs.oracle.com/html/A95915_01/sqopr.htm)
2. MySQL - support
(https://dev.mysql.com/doc/refman/5.0/en/comparison-operators.html)
3. Microsoft SQL Server - not support
(https://msdn.microsoft.com/en-us/library/ms188074.aspx)
4. PostgreSQL - not support
(http://www.postgresql.org/docs/9.2/static/functions-comparison.html)
5. MongoDB - N/A
6. DB 2 - not support
(http://www-01.ibm.com/support/knowledgecenter/ssw_ibm_i_72/sqlp/rbafycompop.htm)
7. Microsoft Access - not support
(https://support.office.com/en-za/article/Table-of-operators-e1bc04d5-8b76-429f-a252-e9223117d6bd)
8. SQLite - not support
(http://www.tutorialspoint.com/sqlite/sqlite_comparison_operators.htm)
9. Cassandra - N/A
10. Redis - N/A
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