esqlj-elastic-jdbc

An open source JDBC driver for Elasticsearch released under Apache License 2.0

esqlj is a JDBC driver for Elastic built on top of Elastic Rest High Level API (rel. 7.11). See Elastic licenses in folder licenses/elastic-licenses

esqlj extend SQL syntax with advanced Elastic query capabilities like full text queries, geo queries, shape queries, joining queries etc.

Sql parsing is provided by jsqlparser library JSQLParser. See related licenses in folder licenses/JSqlParser

About SQL implementation see below section 'Support matrix and conventions'

Project status

Not production ready

DQL implemented
DDL and DML not implemented (actually not in scope)

Driver class

org.fpasti.jdbc.esqlj.EsDriver

JDBC Connections string

JDBC url must to follow this syntax:

jdbc:esqlj:http<s>://<elastic_address_1>:<elastic_port_1>,http://<elastic_address_2>:<elastic_port_2>,...;param1=paramValue1;...

It's possible to declare a pool of connections by comma delimited URLs list.

Optional parameters:

Name	Description	Default value
userName	Credential user name	-
password	Credential password	-
includeTextFieldsByDefault	Include Elastic text typed fields by default on select *	false
indexMetaDataCache	Cache retrieved indices structure (it's suggested to keep enabled this feature because retrieving these information it could be an heavy operation, especially for alias or starred index queries). Best choice to enable it on unmutable index	true
maxGroupByRetrievedElements	Max GROUP BY retrieved elements for selected fields	500
queryScrollFromRows	Number of rows fetched on first pagination	500
queryScrollFetchSize	Fetched rows on next pagination	500
queryScrollTimeoutMinutes	Timeout between pagination expressed in minutes	3
queryScrollOnlyByScrollApi	If true, pagination will be executed by Elastic Scroll API. If false, it will be applied the scroll strategy that best fit the query (see Pagination paragraph below)	true
sharedConnection	If valued true Elastic client internally used by esqlj will be statically shared between all connections (use it if you don't have the requirement to connect to different Elastic clusters inside same JVM)	true

Concepts

Elastic indices are managed like SQL Tables.
Elastic aliases are managed like SQL Views.

Query on indices containing special characters like *, -, . need to be double quoted. Example: 'SELECT * FROM ".test-index*"'
Fields and aliases containing special characters like - must also to be double quoted.

Elastic document identifier "_id" can be fetched in not aggregating query. It's of type string and mapped on MetaData like the index primary key. This column is also available on Where condition for matching query (=, !=).
Search score "_score" is returned like a colum of type float in not aggregating query.

Standard SQL filtering syntax is very limited. Esqlj supports a custom syntax for filtering documents using Elastic API full text queries, geo queries, shape queries...
Actually are implemented only a limited set of these advanced filtering techniques. This is an example that uses Query string ELastic API (query-dsl-query-string-query):

SELECT _id, _score FROM indexName WHERE query_string('(new york city) OR (big apple) OR name:/joh?n(ath[oa]n)/', 'field1, field2,city.*', 'minimum_should_match:2')

By default the maximum number of document fields / columns that can be retrieved is set to 100.
This explains - for example - because by default .kibana_* index containing almost 500 fields return an error on 'select *'.
For increasing this configuration threshold change this Elastic setting according to your needs: 'index.max_docvalue_fields_search'

Change max doc threshold on indices that start with 'my-index':

PUT /my-index*/_settings
{
  "index" : {
    "max_docvalue_fields_search" : 500
  }
}

Change max doc threshold on all indices:

PUT /*/_settings
{
  "index" : {
    "max_docvalue_fields_search" : 500
  }
}

In the future there will no longer be possible query system indices.

Elastic boolean fields are typed BOOLEAN on resultset. Use constants true and false to express conditions on these fields. Example: SELECT * from \"esqlj-test-static-010\" WHERE booleanField=true

DBeaver

A sample usage of esqlj in DBeaver:

Tables are Elasticsearch indices. Views are Elasticsearch aliases

Index fields

Index documents

Sample SQL query

How to configure DBeaver to use esqlj driver (without Elastic login)

• Create a new connection of type Elasticsearch
• Click "Edit Driver Settings"
• Change:
  • Class Name: org.fpasti.jdbc.esqlj.EsDriver
  • URL Template: jdbc:esqlj:http://{host}:{port}
  • Remove all jars and add esqlj-<rel>-shaded.jar (available from project build)
  • Click "OK" to confirm
• Change if required host and port and Test Connection
• OK

Sample usage from Java

Add driver dependency in pom.xml:

<dependency>
	<groupId>org.fpasti</groupId>
	<artifactId>esqlj</artifactId>
	<version>0.2.0</version>
</dependency>

DriverManager.registerDriver(new EsDriver());
Connection connection = DriverManager.getConnection("jdbc:esqlj:http://localhost:9200");
Statement stmt = null;
ResultSet rs = null;

try {
	stmt = connection.createStatement();
	rs = stmt.executeQuery("SELECT * from \"esqlj-test-static-010\" WHERE booleanField=true");

	// print out column & fields
	ResultSetMetaData rsm = rs.getMetaData();
	for(int i = 1; i <= rs.getMetaData().getColumnCount(); i++) {
		System.out.println(String.format("%d: Column: %s, Column Alias: %s, Type: %s", i, rsm.getColumnName(i), rsm.getColumnLabel(i), rsm.getColumnTypeName(i)));
	}

	// iterate over query res
	while (rs.next()) {
		System.out.println(String.format("_id: %s : doubleField: %f - keywordField: %s - textField: %s - score: %f", rs.getString(10), rs.getDouble(2), rs.getObject(5), rs.getString(8), rs.getFloat(11)));
	}

} catch (SQLException ex) {
	System.out.println("SQLException: " + ex.getMessage());
} finally {
	if(stmt != null) {
		stmt.close();
	}
	if(connection != null) {
		connection.close();
	}
}

PreparedStatement actually unimplemented

Types

Mapping of supported Elastic types to SQL types:

Elastic on index type	Metadata declared SQL Type	Java effective type
boolean	BOOL	Boolean
date	TIMESTAMP	LocalDateTime
date_nanos	TIMESTAMP	LocalDateTime
doc_id	VARCHAR	String
double	NUMBER	Double
flattened	STRUCT	Object
float	NUMBER	Float
geo_point	STRUCT	EsGeoPoint
half_float	NUMBER	Float
integer	NUMBER	Integer
ip	VARCHAR	String
keyword	VARCHAR	String
long	BIGINT	Long
object	STRUCT	Object
scaled_float	NUMBER	Float
short	NUMBER	Byte
text	VARCHAR	String
unsigned_long	NUMBER	Long
wildcard	VARCHAR	String

Pagination

By default esqlj implements a scrolling strategy on query through Elastic Scroll API. Optionally it's possibile to activate the less expensive scroll by order, but if you want to activate this functionality pay attention to include in every query a sorting on at least one tiebreaker field (in future it's no longer possible to query by doc id, it could be a best practice to store identifier also in document field). It's in discussion an RFC on Elastic product about the introduction of an automatic tiebreaker in query result. But for now if you enable this feature and miss to add a sorting on a tiebreaker fields some rows could be skipped between paginations of data.

Still on the subject of scrolling by order, the driver doesn't use Point in Time API (it seems missing the support in Elastic Rest High level API).

Pay attention: Scroll API consume resources on server. It's a best practice to fetch all required data as soon as possible. The scroll link will be automatically released from esqlj at the end of data retrieve.

Testing

Most of test units require a live Elastic instance.
The activation of these units is commanded by a system variable named "ESQLJ_TEST_CONFIG".
The environment variabile must concatenate a valid esqlj JDBC url connection string and the load strategy of the documents requested by query inside units:

ESQLJ_TEST_CONFIG=jdbc:esqlj:http://<elastic_address>:<elastic_port>|<createAndDestroy or createOnly>

Parameters	Actions	Scope
createAndDestroy	Test units create index 'esqlj-test-volatile-<uuid>' on start and delete it on finish	Continuous Delivery/Deployment
createOnly	Test units create index 'esqlj-test-static-<release.version>' and not delete it on finish. If it's just present on Elasticsearch it will be preserved. (Will be required a manual delete of it from system).	Development stage

Sample configuration: ESQLJ_TEST_CONFIG="jdbc:esqlj:http://10.77.154.32:9080|createOnly"

If ESQLJ_TEST_CONFIG isn't declared, all tests depending from live connection will be skipped.

Support matrix and conventions

Select clause

Actually supported SELECT [...] elements:

Select element	Notes
column	Elastic document field
column alias or column AS alias	Alias for field in query result
*	All document fields
_id	document identifier (string)
_score	document query search score (float)
TO_CHAR(field, mask_date)	Format date field. Example: TO_CHAR(timestampField, 'YYYY/MM/DD HH:MI:SS'). Supported mask: YEAR, YYYY, YY, MM, MONTH, MON, DDD, DD, HH24, HH12, HH, MI, SS, DAY, XFF, FFF, FF, F, PM, TZR, TZH.
LATITUDE	Extract latitude from EsGeoPoint field (not orderable)
LONGITUDE	Extract longitude from EsGeoPoint field (not orderable)
COUNT(*)	Number of documents in index: SELECT COUNT(*) FROM index
COUNT(field)	Number of documents in index where specified field is present and not null: SELECT COUNT("object.keywordObjectField") FROM index
COUNT(DISTINCT field)	Number of distinct values of specified field in index: SELECT COUNT(DISTINCT keywordField) FROM index

Supported GROUP BY query functions:

Function	Description	Example
AVG	Average of values	SELECT AVG(integerField) FROM index
COUNT(*)	Number of documents	Number of documents in group: SELECT COUNT(*) FROM index
COUNT(field)	Number of documents with specified field	Number of documents in group where specified field is present and not null: SELECT COUNT("object.keywordObjectField") FROM index
COUNT(DISTINCT field)	Number of distinct values	Number of distinct values of specified field: SELECT COUNT(DISTINCT keywordField) FROM index
MAX	Max column value	SELECT MAX(integerField) FROM index
MIN	Min column value	SELECT MIN(integerField) FROM index
SUM	Sum of values	SELECT SUM(integerField) FROM index

Select Distinct

It's possibile to query distinct values using DISTINCT clause.

Example:SELECT DISTINCT keywordField, booleanField FROM index ORDER BY keywordField, booleanField DESC

Where condition

You can use both column name or column alias in expression.

Expression condition	Notes
left expression = value
left expression != value
left expression > numeric_value
left expression >= numeric_value
left expression < numeric_value
left expression <= numeric_value
left expression LIKE expression	Implemented by Wildcard Elasticsearch filter. See Elasticsearch documentation about its usage (query-dsl-wildcard-query)
left expression IS NULL
left expression IS NOT NULL
left expression BETWEEN a AND b	a and b could be NUMBER, STRING, date expressed by TO_DATE('date', 'mask_date'), EXTRACT function
left expression IN (value1, value2, ...)
query_string(...)	Elastic raw query. See below for reference
geo_bounding_box(...)	Elastic raw query. See below for reference

Admitted left expression

Expression
column
alias
EXTRACT(period from column)

value=column expression is for example considered invalid from esqlj

Specific Elastic query functions

esqlj allow you to use specific Elastic query API.
Syntax usage is query_type(param1,param2,...), where query_type maps specific Elastic query; and param1,param2,... allows you to pass parameters to that query.
There are a set of mandatory parameters for every implemented custom query. It's possible also to set optional parameters for changing low level configuration query behaviour, like for example analyze_wildcard, fuzzy_max_expansions etc. These configuration settings must to be declared in this way: query_string('search criteria','field1,field2,object.*','analyze_wildcard:true','fuzzy_max_expansions:15'). Esqlj will dynamically cast params value type according to expected parameter Elastic query object.

Currently implemented raw Elastic queries:

Elastic query	query_type	Parameters	Elastic reference
Query string	query_string	1: query expression, 2: search on fields (* for all), 3..x: additional query parameters (see Elastic documentation)	string_query
Geo bounding box	geo_bounding_box	1: geopoint field, 2: top left latitude, 3: top left: longitude, 4: bottom right latitude, 5: bottom right longitude, 6..x extra params	geo_bounding_box

Specific Elastic query functions samples

Query type	Sample
query_string	SELECT id, _score FROM indexName WHERE query_string('(new york city) OR (big apple) OR name:/joh?n(ath[oa]n)/', 'field1, field2,city.*', 'minimum_should_match:2')
geo_bounding_box	SELECT _id, _score FROM indexName WHERE geo_bounding_box('geoPointField', 50, 8, 40.1, 10.2)

Functions

Function name	Admitted on	Notes
SYSDATE	Right expression	Current date time
SYSDATE()	Right expression	Current date time
NOW()	Right expression	Current date time
GETDATE()	Right expression	Current date time
TRUNC(SYSDATE|SYSDATE())	Right expression	Current date
TO_DATE(date, mask_date)	Right expression	Supported mask: YEAR, YYYY, YY, MM, MONTH, MON, DDD, DD, HH24, HH12, HH, MI, SS, DAY, XFF, FFF, FF, F, PM, TZR, TZH. Example TO_DATE('2020/01/01', 'YYYY/MM/DD')
EXTRACT(PERIOD FROM column)	Left expression	PERIOD can be valued with YEAR, MONTH, DAY, HOUR, MINUTE, SECOND. Usage example: EXTRACT(YEAR FROM timestamp)!=2020

Group by

It's possible to aggregate values using GROUP BY clause.

Example: SELECT booleanField, AVG(integerField) test, SUM(longField), COUNT(doubleField), COUNT(*) from testIndex GROUP BY booleanField

Having

It's possible to apply filtering on Group by expressions.

Example:
SELECT booleanField, AVG(integerField) test, SUM(longField), COUNT(*) from testIndex GROUP BY booleanField HAVING AVG(integerField)>=4 OR SUM(longField)>=19

Order

Example:
SELECT * FROM column ORDER BY keywordField, integerField DESC

Limit

Example:
SELECT * FROM column LIMIT 100

Compatibility

Tested on 7.4.2 and 7.10.0 Elasticsearch release

About me

Fabrizio Pasti
fabrizio.pasti@gmail.com
https://www.linkedin.com/in/fabrizio-pasti-2340a627