tMysqlSCD Properties - 6.1

Talend Open Studio for Big Data Components Reference Guide

Talend Open Studio for Big Data
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tMysqlSCD reflects and tracks changes in a dedicated MySQL SCD table.


tMysqlSCD addresses Slowly Changing Dimension needs, reading regularly a source of data and logging the changes into a dedicated SCD table

Basic settings

Property type

Either Built-in or Repository.

Since version 5.6, both the Built-In mode and the Repository mode are available in any of the Talend solutions.



Built-in: No property data stored centrally.



Repository: Select the Repository file where properties are stored. The following fields are pre-filled in using fetched data.


Use an existing connection

Select this check box and in the Component List click the relevant connection component to reuse the connection details you already defined.


When a Job contains the parent Job and the child Job, if you need to share an existing connection between the two levels, for example, to share the connection created by the parent Job with the child Job, you have to:

  1. In the parent level, register the database connection to be shared in the Basic settings view of the connection component which creates that very database connection.

  2. In the child level, use a dedicated connection component to read that registered database connection.

For an example about how to share a database connection across Job levels, see Talend Studio User Guide.


DB Version

Select the Mysql version you are using.



Database server IP address.



Listening port number of DB server.



Name of the database.


Username and Password

DB user authentication data.

To enter the password, click the [...] button next to the password field, and then in the pop-up dialog box enter the password between double quotes and click OK to save the settings.



Name of the table to be written. Note that only one table can be written at a time.


Action on table

On the table defined, you can perform one of the following operations:

None: No operation is carried out.

Create a table: The table does not exist and gets created.

Create a table if not exists: The table is created if it does not exist.


Schema and Edit schema

A schema is a row description. It defines the number of fields (columns) to be processed and passed on to the next component. The schema is either Built-In or stored remotely in the Repository.

Since version 5.6, both the Built-In mode and the Repository mode are available in any of the Talend solutions.

Click Edit schema to make changes to the schema. If the current schema is of the Repository type, three options are available:

  • View schema: choose this option to view the schema only.

  • Change to built-in property: choose this option to change the schema to Built-in for local changes.

  • Update repository connection: choose this option to change the schema stored in the repository and decide whether to propagate the changes to all the Jobs upon completion. If you just want to propagate the changes to the current Job, you can select No upon completion and choose this schema metadata again in the [Repository Content] window.



Built-in: The schema is created and stored locally for this component only. Related topic: see Talend Studio User Guide.



Repository: The schema already exists and is stored in the Repository, hence can be reused. Related topic: see Talend Studio User Guide.


SCD Editor

The SCD editor helps to build and configure the data flow for slowly changing dimension outputs.

For more information, see SCD management methodologies.


Use memory saving mode

Select this check box to maximize system performance.


Source keys include Null

Select this check box to allow the source key columns to have Null values.


Special attention should be paid to the uniqueness of the source key(s) values when this option is selected.


Die on error

This check box is cleared by default, meaning to skip the row on error and to complete the process for error-free rows.

Advanced settings

Additional JDBC Parameters

Specify additional connection properties for the DB connection you are creating. This option is not available if you have selected the Use an existing connection check box in the Basic settings.


End date time details

Specify the time value of the SCD end date time setting in the format of HH:mm:ss. The default value for this field is 12:00:00.

This field appears only when SCD Type 2 is used and Fixed year value is selected for creating the SCD end date. For more information about SCD Type 2, see SCD management methodologies.


tStatCatcher Statistics

Select this check box to collect log data at the component level.


Debug mode

Select this check box to display each step during processing entries in a database.

Dynamic settings

Click the [+] button to add a row in the table and fill the Code field with a context variable to choose your database connection dynamically from multiple connections planned in your Job. This feature is useful when you need to access database tables having the same data structure but in different databases, especially when you are working in an environment where you cannot change your Job settings, for example, when your Job has to be deployed and executed independent of Talend Studio.

The Dynamic settings table is available only when the Use an existing connection check box is selected in the Basic settings view. Once a dynamic parameter is defined, the Component List box in the Basic settings view becomes unusable.

For examples on using dynamic parameters, see Scenario 3: Reading data from MySQL databases through context-based dynamic connections and Scenario: Reading data from different MySQL databases using dynamically loaded connection parameters. For more information on Dynamic settings and context variables, see Talend Studio User Guide.

Global Variables

NB_LINE_UPDATED: the number of rows updated. This is an After variable and it returns an integer.

NB_LINE_INSERTED: the number of rows inserted. This is an After variable and it returns an integer.

NB_LINE_REJECTED: the number of rows rejected. This is an After variable and it returns an integer.

ERROR_MESSAGE: the error message generated by the component when an error occurs. This is an After variable and it returns a string. This variable functions only if the Die on error check box is cleared, if the component has this check box.

A Flow variable functions during the execution of a component while an After variable functions after the execution of the component.

To fill up a field or expression with a variable, press Ctrl + Space to access the variable list and choose the variable to use from it.

For further information about variables, see Talend Studio User Guide.


This component is used as Output component. It requires an Input component and Row main link as input.

SCD management methodologies

Slowly Changing Dimensions (SCDs) are dimensions that have data that slowly changes. The SCD editor offers the simplest method of building the data flow for the SCD outputs. In the SCD editor, you can map columns, select surrogate key columns, and set column change attributes through combining SCD types.

The following figure illustrates an example of the SCD editor.

SCD keys

You must choose one or more source keys columns from the incoming data to ensure its unicity.

You must set one surrogate key column in the dimension table and map it to an input column in the source table. The value of the surrogate key links a record in the source to a record in the dimension table. The editor uses this mapping to locate the record in the dimension table and to determine whether a record is new or changing. The surrogate key is typically the primary key in the source, but it can be an alternate key as long as it uniquely identifies a record and its value does not change.

Source keys: Drag one or more columns from the Unused panel to the Source keys panel to be used as the key(s) that ensure the unicity of the incoming data.

Surrogate keys: Set the column where the generated surrogate key will be stored. A surrogate key can be generated based on a method selected on the Creation list.

Creation: Select any of the below methods to be used for the key generation:

Auto increment: auto-incremental key.

Input field: key is provided in an input field.

When selected, you can drag the appropriate field from the Unused panel to the complement field.

Routine: from the complement field, you can press Ctrl+ Space to display the autocompletion list and select the appropriate routine.

Table max +1: the maximum value from the SCD table is incremented to create a surrogate key.

DB Sequence: from the complement field, you can enter the name of the existing database sequence that will automatically increment the column indicated in the name field.


This option is only available through the SCD Editor of the tOracleSCD component.

Combining SCD types

The Slowly Changing Dimensions support four types of changes: Type 0 through Type 3. You can apply any of the SCD types to any column in a source table by a simple drag-and-drop operation.

Type 0: is not used frequently. Some dimension data may be overwritten and other may stay unchanged over time. This is most appropriate when no effort has been made to deal with the changing dimension issues.

Type 1: no history is kept in the database. New data overwrites old data. Use this type if tracking changes is not necessary. this is most appropriate when correcting certain typos, for example the spelling of a name.

Type2: the whole history is stored in the database. This type tracks historical data by inserting a new record in the dimensional table with a separate key each time a change is made. This is most appropriate to track updates, for example.

SCD Type 2 principle lies in the fact that a new record is added to the SCD table when changes are detected on the columns defined. Note that although several changes may be made to the same record on various columns defined as SCD Type 2, only one additional line tracks these changes in the SCD table.

The SCD schema in this type should include SCD-specific extra columns that hold standard log information such as:

-start: adds a column to your SCD schema to hold the start date. You can select one of the input schema columns as a start date in the SCD table.

-end: adds a column to your SCD schema to hold the end date value for a record. When the record is currently active, the end date is NULL or you can select Fixed Year Value and fill in a fictive year to avoid having a null value in the end date field.

-version: adds a column to your SCD schema to hold the version number of the record.

-active: adds a column to your SCD schema to hold the true or false status value. this column helps to easily spot the active record.

Type 3: only the information about a previous value of a dimension is written into the database. This type tracks changes using separate columns. This is most appropriate to track only the previous value of a changing column.