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[SPARK-10180] [SQL] JDBCRDD does not process EqualNullSafe filter. #8391

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[SPARK-10180] [SQL] JDBCRDD does not process EqualNullSafe filter. #8391

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[SPARK-10180] [SQL] JDBCRDD does not process EqualNullSafe filter.
HyukjinKwon Aug 24, 2015
f76021d
[SPARK-10180] [SQL] Rewirte null-safe equality operator as using isnu…
HyukjinKwon Aug 25, 2015
4fe4b06
[SPARK-10180] [SQL] Add some comments and round brackets
HyukjinKwon Aug 25, 2015
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1 change: 1 addition & 0 deletions sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/jdbc/JDBCRDD.scala
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Expand Up @@ -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)}"
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@rxin rxin Aug 24, 2015

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just to double check - is this standard sql?

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@rxin rxin Aug 24, 2015

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(standard as in -- do most database systems support this?)

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@HyukjinKwon HyukjinKwon Aug 25, 2015

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I thought the comparison operator is official and a standard one (because both I am used to MySQL and thought Spark and Hive use 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't 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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@HyukjinKwon HyukjinKwon Aug 25, 2015

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Do you think this should be treated differently for each different dialect ( maybe only for MySQL ) or should this be closed?

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@rxin rxin Aug 25, 2015

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Since this is only in MySQL, I think the only options are:

  1. don't support it
  2. rewrite it as using isnull and normal equality.
  3. add it to dialect.

Don't have a strong preference here. If 2 is not much slower, maybe just do 2?

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@HyukjinKwon HyukjinKwon Aug 25, 2015

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Yes I will go for the second one with some comments. Thanks :)

case LessThan(attr, value) => s"$attr < ${compileValue(value)}"
case GreaterThan(attr, value) => s"$attr > ${compileValue(value)}"
case LessThanOrEqual(attr, value) => s"$attr <= ${compileValue(value)}"
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