Extracted Exasol dialect, removed deprecated properties

Summary

In this release we introduced a few major changes:

1. We extracted the Exasol dialect to a separate repository. The Exasol dialect is not included into a jar of this project anymore. Please, check the latest release of the Exasol dialect here: https://github.com/exasol/exasol-virtual-schema/releases

2. We removed deprecated Virtual Schema properties CONNECTION_STRING, USERNAME and PASSWORD. Please, use CONNECTION_NAME property instead.

3. We updated API and documentation.

Some other minor changes see in the list of changes.

Changes

• #289: removed deprecated properties
• #302: removed old integration test dependencies, updated all other dependencies
• #322: ported VS to VSCJDBC 3.0.0
• #324: added API description for JSON functions
• #333: updated dependencies and fixed incompatibilities issues (#334)

MySQL dialect improvements

Summary

This release contains a fix for TEXT data type mapping and improved documentation for MySQL dialect.

Changes

• #320: hardcoded the size of MySQL data type TEXT.

Documentation improvements

Summary

This release contains documentation improvements.

Changes

• #310: Improved documentation.
• #318: Replaced JAVA_TOOL_OPTIONS by %jvmoptions.

BigQuery dialect improvements

Summary

In this release we worked on improvements for BigQuery dialect.

Changes

#288: Fixed and improved data types mapping, fixed bug with an error when a table is empty, fixed bug with NULLs mapping, improved documentation, tested with the latest driver.
#314: Internal speed improvements, documentation improvements.

Rewrote integration tests with test-containers framework

Summary

In this release we refactored the structure of the project and rewrote integration tests with test-containers framework.

Changes

• #295: Removed dist module.
• #287: Removed an unsupported capability from MySQL dialect.
• #223: Rewrote Exasol integration test.
• #300: Rewrote PostgreSQL integration test.
• #302: Removed old integration tests dependencies.
• #303: Rewrote Oracle integration test.
• #305: Rewrote Hive integration test.
• #307: Removed old integration tests classes.
• Update README.md

Refactoring common JDBC parts and minor bugs fixes

Summary

In this release we extracted common JDBC parts to a separate maven module
It also contains documentation improvements and minor bugs fixes.

Changes

• #280: Extract common JDBC parts to separate maven module.
• #280: Ported to Java 11.
• #291: Adjusted hashtype.
• Fixed reference to Apache Parquet files.
• Fixed named connection reference.
• Added logo.

HASHTYPE support, improvements for documentation and bug fixes

Summary

This release introduces a new Exasol data type: HASHTYPE.
It also contains documentation improvements and minor bugs fixes.

Changes

• #270: Added support for ROWID column type in Oracle.
• #191: Rewrote creating dialect documentation.
• #254: Moved dialect specific classes to appropriate packages.
• #272: Fixed NullPointerException for setProperties request.
• #281: Updated SQL SERVER documentation.
• #240: Added HASHTYPE support.

Added catalog support to MySQL

Summary

As MySQL JDBC driver maps both catalog and schema to database, we replaced schema support with catalog support. It allows to narrow scanning scanning to the selected catalog.

Changes

• #267: Added catalog support and removed schema support,

MySQL SQL Dialect

Summary

In this release we added implementation for MySQL JDBC adapter.

Changes

• #257: Implemented MySQL dialect.

Java 9 port, Oracle and Hive dialect improvements

Summary

We ported Virtual Schema to Java 9 and improved the Oracle SQL dialect. We also removed the deprecated adapter entry point. Please use the entry point

com.exasol.adapter.RequestDispatcher

in all your CREATE JAVA ADAPTER SCRIPT statements.

Note: you need Exasol 6.2 or later to run Virtual Schema 2.0.0 and above.

Unrecognized and Unsupported Data Types

Not all data types present in a source database have a matching equivalent in Exasol. Also software updates on the source database can introduce new data type that the Virtual schema does not recognize.

In version 2.0.0 we changed the handling of those types.

There are a few important things you need to know about those data types.

1. Columns of an unrecognized / unsupported data type are not mapped in a Virtual Schema. From Exasol's perspective those columns do not exist on a table. This is done so that tables containing those columns can still be mapped and do not have to be rejected as a whole.
2. You can't query columns of an unrecognized / unsupported data type. If the source table contains them, you have to explicitly exclude them from the query. You can for example not use the asterisk (*) on a table that contains one ore more of those columns. This will result in an error issued by the Virtual schema.
3. You can't use functions that result in an unsupported / unknown data type.

Example

Source table:

T1(C1 VARCHAR, C2 BLOB, C3 DATE);

Mapped table in Exasol:

T2(C1 VARCHAR, C3 DATE);

Caveats

Note that there is a special pitfall when you select all supported columns in a table by ID where the tables has unsupported column data types. The optimizer in the core Exasol database recognizes that all columns that it is aware of are selected. It does not know about the unsupported ones and optimizes the list to a SELECT *. The problem then is that the resulting push-down query will select all source columns, including the unsupported ones. That way the result dataset will have unsupported columns.

To circumvent that problem, you need to modify the select list in a way that does not allow this optimization. For example by adding a pseudo-column with a constant.

Changes in Hive dialect

Added HIVE_CAST_NUMBER_TO_DECIMAL_WITH_PRECISION_AND_SCALE property in Hive dialect which can be used when you want to have decimal numbers even if the precision is bigger than Exasol's maximum precision. Please read Hive dialect documentation for further details.

Changes

• #249: Improved CLOB handling in Oracle dialect.
• #247: Ported Virtual Schemas to Java 9.
• #243: Oracle timestamps now converted to Exasol timestamps instead of VARCHAR.
• #241: BLOB now not mapped anymore in Oracle dialect.
• #252: Improved handling of unsupported column in SELECT *
• #176: Added HIVE_CAST_NUMBER_TO_DECIMAL_WITH_PRECISION_AND_SCALE property in Hive dialect