Anonymous block in Query Service

Last update: 2024-01-09
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Adobe Experience Platform Query Service supports anonymous blocks. The anonymous block feature allows you to chain one or more SQL statements that are executed in sequence. They also allow for the option of exception-handling.

The anonymous block feature is an efficient way to perform a sequence of operations or queries. The chain of queries within the block can be saved as a template and scheduled to run at a particular time or interval. These queries can be used to write and append data to create a new data set and are typically used where you have a dependency.

The table provides a breakdown of the block’s main sections: execution, and exception-handling. The sections are defined by the keywords BEGIN, END, and EXCEPTION.

section description
execution An executable section starts with the keyword BEGIN and ends with the keyword END. Any set of statements included within the BEGIN and END keywords will be executed in sequence and ensures that subsequent queries will not execute until the previous query in the sequence has been completed.
exception-handling The optional exception-handling section starts with the keyword EXCEPTION. It contains the code to catch and handle exceptions should any of the SQL statements in the execution section fail. If any of the queries fail, the entire block is stopped.

It is worth noting that a block is an executable statement and can therefore be nested within other blocks.

NOTE

It is strongly recommended to test your queries on smaller datasets and ensure that they work as expected. If a query has a syntax error then the exception will be thrown and the entire block will be aborted. Once you have verified the integrity of the queries you may begin to chain them. This ensures that the block works as expected before you put them into operation.

Sample anonymous block queries

The following query shows an example of chaining SQL statements. See the SQL syntax in Query Service document for more information on any of the SQL syntax used.

$$ BEGIN
    CREATE TABLE ADLS_TABLE_A AS SELECT * FROM ADLS_TABLE_1....;
    ....
    CREATE TABLE ADLS_TABLE_D AS SELECT * FROM ADLS_TABLE_C....;
    EXCEPTION WHEN OTHER THEN SET @ret = SELECT 'ERROR';
END
$$;

In the example below, SET persists the result of a SELECT query in the specified local variable. The variable is scoped to the anonymous block.

The snapshot ID is stored as a local variable (@current_sid). It is then used in the next query to return results based on the SNAPSHOT from the same dataset/table.

A database snapshot is a read-only, static view of a SQL Server database. For more information on the snapshot clause see the SQL syntax documentation.

$$ BEGIN
  SET @current_sid = SELECT parent_id  FROM (SELECT history_meta('your_table_name')) WHERE  is_current = true;
  CREATE temp table abcd_temp_table AS SELECT count(1) FROM your_table_name  SNAPSHOT SINCE @current_sid;
END
$$;

Anonymous block with third-party clients

Certain third-party clients may require a separate identifier before and after an SQL block to indicate that a part of the script should be handled as a single statement. If you receive an error message when using Query Service with a third-party client, you should refer to the documentation of the third-party client regarding the use of an SQL block.

For example, DbVisualizer requires that the delimiter must be the only text on the line. In DbVisualizer, the default value for the Begin Identifier is --/ and for the End Identifier it is /. An example of an anonymous block in DbVisualizer is seen below:

--/
$$ BEGIN
    CREATE TABLE ADLS_TABLE_A AS SELECT * FROM ADLS_TABLE_1....;
    ....
    CREATE TABLE ADLS_TABLE_D AS SELECT * FROM ADLS_TABLE_C....;
    EXCEPTION WHEN OTHER THEN SET @ret = SELECT 'ERROR';
END
$$;
/

For DbVisualizer in particular, there is also an option in the UI to “Execute the complete buffer as one SQL statement”. See the DbVisualizer documentation for more information.

Next steps

By reading this document, you now have a clear understanding of anonymous blocks and how they are structured. Please read the query execution guide for more information on writing queries.

You should also read about how anonymous blocks are used with the incremental load design pattern to increase query efficiency.

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