Short Description
    DBJoin Attributes
    Best Practices
    See also

    Short Description

    DBJoin receives data through a single input port and joins it with data from a database table. These two data sources can potentially have different metadata structures.

    ComponentSame input metadataSorted inputsSlave inputsOutputsOutput for drivers without slaveOutput for slaves without driverJoining based on equalityAuto-propagated metadata
    DBJoin1 (virtual)1-2


    After the data from an input port and database table are joined, they are sent to the first output port. The second output port can optionally be used to capture unmatched master records.

    Port typeNumberRequiredDescriptionMetadata
    Input0Master input portAny
    1 (virtual)Slave input portAny
    Output0Output port for the joined dataAny

    The optional output port for master data records without slave matches. (Only if the Join type attribute is set to Inner join.) This applies only to LookupJoin and DBJoin.

    Input 0


    DBJoin propagates metadata from the first input port to the second output port and vice versa.

    DBJoin has no metadata template.

    If mapping is not defined, DBJoin requires output metadata to match metadata of a query result. If mapping is defined, metadata of a query result must match metadata defined in the DBJoin attribute.

    DBJoin Attributes

    AttributeReqDescriptionPossible values
    Join keyyes

    Key according to which the incoming data flows are joined. See Join Key.

    Left outer join 

    If set to true, driver records without corresponding slave are parsed, as well. Otherwise, inner join is performed.

    false (default) | true
    DB connectionyesThe ID of a DB connection to be used as a resource of slave records. 
    DB metadata 

    The ID of DB metadata to be used. If not set, metadata is extracted from a database using an SQL query.

    Query URL[1]The name of an external file, including the path, defining an SQL query. 
    SQL query[1]The SQL query defined in a graph. 
    Transform [2] [3] Transformation in CTL or Java defined in the graph. 
    Transform URL [2] [3] An external file defining the transformation in CTL or Java. 
    Transform class [2] [3] An external transformation class. 
    Cache size The maximum number of records with different key values that can be stored in memory.100 (default)
    Transform source charset 

    Encoding of an external file defining the transformation.

    The default encoding depends on DEFAULT_SOURCE_CODE_CHARSET in defaultProperties.

    E.g. UTF-8
    Error actions 

    The definition of an action that should be performed when the specified transformation returns an Error code. See Return Values of Transformations.

    Error log 

    A URL of the file to which error messages for specified Error actions should be written. If not set, they are written to Console.


    [1]  One of these attributes must be specified. If both are defined, Query URL has the highest priority.

    [2]  One of these transformation attributes should be set. Any of them must use a common CTL template for Joiners or implement a RecordTransform interface.

    For more information, see CTL Scripting Specifics or Java Interfaces.

    For detailed information about transformations, see also Defining Transformations.

    [3]  A unique exception is the case when none of these three attributes are specified, but the SQL query attribute defines what records will be read from the DB table. Values of Join key contained in the input records serve to select the records from db table. These are unloaded and sent unchanged to the output port without any transformation.


    Join Key

    DBJoin receives data through a single input port and joins it with data from a database table. These two data sources can potentially have different metadata structure. It is a general purpose joiner usable in most common situations. It does not require the input to be sorted and is very fast as data is processed in memory.

    The data attached to the first input port is called master, the second data source is called slave. Its data is considered as if it were incoming through the second (virtual) input port. Each master record is matched to the slave record on one or more fields known as a join key. The output is produced by applying a transformation that maps joined inputs to the output.

    Join Key

    Join key is a sequence of field names from a master data source separated from each other by a semicolon, colon, or pipe. You can define the key in the Edit key wizard.

    The order of these field names must correspond to the order of the key fields from the database table (and their data types). The slave part of Join key must be defined in the SQL query attribute.

    One of the query attributes must contain the expression of the following form: ... where field_K=? and field_L=?.

    Example 58.1. Join Key for DBJoin


    This is the master part of fields that should serve to join master records with slave records.

    The SQL query must contain an expression that can look like this:

    ... where fname=? and lname=?

    Corresponding fields will be compared and matching values will serve to join master and slave records.


    The transform in DBJoin lets you define a transformation that sends records to the first output port. The unjoined master records sent to the second output port cannot be modified within the DBJoin transformation.

    CTL Scripting Specifics

    All Joiners share the same transformation template which can be found in CTL Templates for Joiners.

    For detailed information about CloverDX Transformation Language, see Part X, CTL2 - CloverDX Transformation Language.

    Java Interfaces

    If you define your transformation in Java, it must implement the following interface that is common for all Joiners:

    Java Interfaces for Joiners

    See Public CloverDX API.


    Joining on Exact Key

    Input records contain one field customerId with values:


    The customers database table has the following structure and data:

    customer_id | customer_name | customer_surname
     1          | John          | Doe
     3          | Anna          | Smith
    10          | Jane          | Brown

    Join incoming records with data from the database on customerId.


    Create input metadata with one field customerId (integer) and output metadata with the customerId (integer), customerName (string), customerSurname (string) fields.

    Set the Join key and SQL query attributes of DBJoin.

    Join keycustomerId
    DBConnectionYour DBConnection
    SQL queryselect * from "customers" where customer_id=?

    Only records with customerId found in the database are sent to output.

    Matching Range

    Input records contain a product code and date of order.

    productCode | orderDate
    1           | 2015-10-20
    2           | 2015-10-30
    1           | 2015-11-06

    Price of a particular product on particular date can be found in the database.

    productCode | dateFrom   | dateTo     | price 
    1           | 2014-01-01 | 2015-10-31 |  10.99
    1           | 2015-11-01 | 2099-12-31 |  14.99
    2           | 2015-07-01 | 2099-12-31 | 109.99

    Match the price to particular product orders.


    Create input metadata (productCode, orderDate), output metadata (productCode, orderDate, price) and metadata for DBJoin ( productCode, price).

    Set attributes:

    Join keyproduct;orderDate;orderDate
    DBConnectionYour DBConnection
    SQL query select product_id,price_per_unit from "dbjoin_example_02" where product_id=? and valid_from<=? and ?<=valid_to
    TransformSee the code below.
    function integer transform() {
        $out.0.* = $in.0.*;
        $out.0.* = $in.1.*;
        return ALL;

    Best Practices

    If the transformation is specified in an external file (with Transform URL), we recommend users to explicitly specify Transform source charset.


    VersionCompatibility Notice
    4.2.0-M1DBJoin now propagates metadata between the first input port and the second output port.