BEGIN MLOAD

Translation specification for the BEGIN MLOAD and related commands.

The transformation for the command .BEGIN MLOAD is a multi-part transformation that requires the .LAYOUT, .FIELD, .FILLER,.DML LABEL, and .IMPORT commands to simulate its behavior correctly.

This transformation is fully explained in the following subsections.

.LAYOUT, .FIELD and .FILLER

The transformation for the commands .LAYOUT, .FIELD, and .FILLER will create variable definitions to be used in a future function call of the IMPORT of this layout.

Teradata (MultiLoad)

.LAYOUT INFILE_LAYOUT;
.FIELD TABLE_ID        * INTEGER;
.FIELD TABLE_DESCR     * CHAR(8);
.FILLER COL1           * CHAR(1);
.FIELD TABLE_NBR       * SMALLINT;
.FIELD TABLE_SOMEFIELD * SMALLINT;

Snowflake (Python)

  INFILE_LAYOUT_TableName = "INFILE_LAYOUT_TEMP_TABLE"
  INFILE_LAYOUT_Columns = """TABLE_ID INTEGER, 
TABLE_DESCR CHAR(8), 
COL1 CHAR(1), 
TABLE_NBR SMALLINT, 
TABLE_SOMEFIELD SMALLINT"""
  INFILE_LAYOUT_Conditions = """TABLE_ID AS TABLE_ID, TABLE_DESCR AS TABLE_DESCR, COL1 AS COL1, TABLE_NBR AS TABLE_NBR, TABLE_SOMEFIELD AS TABLE_SOMEFIELD"""

.DML LABEL

The transformation for the .DML LABELcommand will create a function containing the statements after the label definition. Note that after the .DML LABEL command there is usually an Insert, Update or Delete.

Teradata (MultiLoad)

-- Example of .DML LABEL with INSERT:
.DML LABEL INSERT_TABLE;                                                                                    
INSERT INTO mydb.mytable( TABLE_ID,TABLE_DESCR,TABLE_NBR ) VALUES( :TABLE_ID,:TABLE_DESCR,:TABLE_NBR );

-- Example of .DML LABEL with DELETE:
.DML LABEL DELETE_TABLE;              
DELETE FROM Employee WHERE EmpNo  = :EmpNo;

-- Example of .DML LABEL with an UPDATE, followed by an INSERT:
.DML LABEL UPSERT_TABLE DO INSERT FOR MISSING UPDATE ROWS;
UPDATE   mydb.mytable SET TABLE_ID = :TABLE_ID WHERE TABLE_DESCR = :somedescription
INSERT INTO mydb.mytable(TABLE_ID, TABLE_DESCR, TABLE_NBR) VALUES(:TABLE_ID, :TABLE_DESCR, :TABLE_NBR );

Snowflake (Python)

  def INSERT_TABLE(tempTableName, queryConditions = ""):
    exec(f"""INSERT INTO mydb.mytable (TABLE_ID, TABLE_DESCR, TABLE_NBR)
SELECT
   SRC.TABLE_ID,
   SRC.TABLE_DESCR,
   SRC.TABLE_NBR
FROM {tempTableName} SRC {queryConditions}""")
  exec("""
    DELETE FROM
      Employee
    WHERE
      EmpNo = :EmpNo
    """)
  def UPSERT_TABLE(tempTableName, queryConditions = ""):
    exec(f"""MERGE INTO mydb.mytable TGT USING (SELECT * FROM {tempTableName} {queryConditions}) SRC ON TGT.TABLE_DESCR = :somedescription
WHEN MATCHED THEN UPDATE SET
   TGT.TABLE_ID = SRC.TABLE_ID
WHEN NOT MATCHED THEN INSERT (TGT.TABLE_ID, TGT.TABLE_DESCR, TGT.TABLE_NBR)
VALUES (SRC.TABLE_ID, SRC.TABLE_DESCR, SRC.TABLE_NBR)""")

.IMPORT

The transformation of the .IMPORT command will create a call to theimport_file_to_temptablehelper to load the data from the file to a temporary table. Then, the calls to all theAPPLYlabels used in the original import will be created. Finally, the calls for anINSERTlabel will be transformed to a query parameter and optionally can have a query condition.

Teradata (MultiLoad)

.IMPORT INFILE INFILE_FILENAME
    LAYOUT INFILE_LAYOUT
    APPLY INSERT_TABLE
    APPLY UPSERT_TABLE
    Apply DELETE_TABLE;

Snowflake (Python)

  snowconvert.helpers.import_file_to_temptable(fr"INFILE_FILENAME", INFILE_LAYOUT_TableName, INFILE_LAYOUT_Columns, INFILE_LAYOUT_Conditions, ',')
  INSERT_TABLE(INFILE_LAYOUT_TableName)
  UPSERT_TABLE(INFILE_LAYOUT_TableName)
  DELETE_TABLE(INFILE_LAYOUT_TableName)
  exec(f"""DROP TABLE {INFILE_LAYOUT_TableName}""")

Large Example

Given the transformations shown above for a variety of commands, consider the following example.

With this input data:

id,name,age
1,John,25
2,Maria,29
3,Carlos,31
4,Mike,40
5,Laura,27

Teradata (MultiLoad)

.begin import mload
        tables
	mySampleTable1
sessions 20
ampcheck none;

.layout myLayOut;
 .field ID * VARCHAR(2) NULLIF ID = '1';
 .field NAME * VARCHAR(25);
 .field AGE * VARCHAR(10);
.dml label insert_data;

INSERT INTO mySampleTable1
 ( 
    ID,
    NAME,
    AGE	
 )
VALUES
 (
    :ID,
    SUBSTRING(:NAME FROM 2),
    :AGE
 );

.import infile sampleData.txt
layout myLayOut
apply insert_data

.end mload;
.logoff;

Snowflake (Python)

#*** Generated code is based on the SnowConvert Python Helpers version 2.0.6 ***
 
import os
import sys
import snowconvert.helpers
from snowconvert.helpers import Export
from snowconvert.helpers import exec
from snowconvert.helpers import BeginLoading
con = None
def main():
  snowconvert.helpers.configure_log()
  con = snowconvert.helpers.log_on()
  #** MSC-WARNING - MSCEWI1002 - REMOVED NEXT STATEMENT, NOT APPLICABLE IN SNOWFLAKE.  **
  #.begin import mload tables mySampleTable1 sessions 20 ampcheck none
   
  myLayOut_TableName = "myLayOut_TEMP_TABLE"
  myLayOut_Columns = """ID VARCHAR(2), 
NAME VARCHAR(25), 
AGE VARCHAR(10)"""
  myLayOut_Conditions = """CASE
   WHEN ID = '1'
      THEN NULL
   ELSE ID
END AS ID, NAME AS NAME, AGE AS AGE"""
  def insert_data(tempTableName, queryConditions = ""):
    exec(f"""INSERT INTO mySampleTable1 (ID, NAME, AGE)
SELECT
   SRC.ID,
   SUBSTRING(SRC.NAME, 2),
   SRC.AGE
FROM {tempTableName} SRC {queryConditions}""")
  #** MSC-WARNING - MSCEWI1002 - REMOVED NEXT STATEMENT, NOT APPLICABLE IN SNOWFLAKE. TRANSLATED BELOW **
  #.import infile sampleData.txt layout myLayOut apply insert_data
   
  snowconvert.helpers.import_file_to_temptable(fr"sampleData.txt", myLayOut_TableName, myLayOut_Columns, myLayOut_Conditions, ',')
  insert_data(myLayOut_TableName)
  exec(f"""DROP TABLE {myLayOut_TableName}""")

  if con is not None:
    con.close()
    con = None
  snowconvert.helpers.quit_application()

if __name__ == "__main__":
  main()

Known Issues

1. Delete statement is partially supported

The DELETE statement is partially supported since the where conditions, when found, are not being converted correctly if pointing to a LAYOUT defined column.

In the example below, :EmpNo is pointing to a LAYOUT defined column. However, the transformation does not take this into account and thus the code will be referencing a column that does not exists.

  exec("""
    DELETE FROM
      Employee
    WHERE
      EmpNo = :EmpNo
    """)

If you have any additional questions regarding this documentation, you can email us at snowconvert-support@snowflake.com.

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