Set param = dbCmd.CreateParameter("myvalue", adDecimal, adParamInput, 0, myvalue)

param.NumericScale = 4

param.Precision = 13

CREATE TABLE mytable ( 

  id SMALLINT AUTO_INCREMENT PRIMARY KEY, 

  dec1 DECIMAL(13,4),

  dec2 DECIMAL(13,4)

); 

Public Sub test()

    WriteToDB 123456789.1234, 123456789.1234

    WriteToDB 214748.3647, 214748.3647

    WriteToDB 214748.3648, 214748.3648

End Sub

Public Sub WriteToDB(dec1 As Variant, dec2 As Variant)

    Dim dbConn As ADODB.Connection

    Dim dbCmd As ADODB.Command

    Dim sql As String

    Dim param As ADODB.Parameter

    'Open database connection

    Set dbConn = New ADODB.Connection

    dbConn.Open "Provider=MSDASQL;DSN=XXX;DATABASE=XXX;UID=XXX;PWD=XXX;"

    Set dbCmd = New ADODB.Command

    dbCmd.ActiveConnection = dbConn

    dbCmd.CommandType = adCmdText

    'Define command and parameters

    sql = "INSERT INTO mytable (dec1, dec2) VALUES (?, ?)"

    Set param = dbCmd.CreateParameter("dec1", adDecimal, adParamInput, 0, dec1)

    param.NumericScale = 4

    param.Precision = 13

    dbCmd.Parameters.Append param

    Set param = dbCmd.CreateParameter("dec2", adDouble, adParamInput, 0, dec2)

    dbCmd.Parameters.Append param

    'Execute command

    dbCmd.CommandText = sql

    dbCmd.Execute , , adExecuteNoRecords

    'Close connection

    dbConn.Close

End Sub

MariaDB [XXX]> SELECT * FROM mytable;

+----+--------------+----------------+

| id | dec1         | dec2           |

+----+--------------+----------------+

|  1 |  191227.7282 | 123456789.1234 |

|  2 |  214748.3647 |    214748.3647 |

|  3 | -214748.3640 |    214748.3648 |

+----+--------------+----------------+