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The standard group is called such because it's a flexible, general use group that can be adapted to a variety of situations. The data model is row based, with items mapping to columns and the data corresponding to a specific row of a table.
The standard group contains items, which may be mapped to the database, or used internally for features such as triggering or handshakes. Items that are mapped to the database target a specific column of a single specific row, chosen according to the group settings. Items can be mapped in a one-way fashion, or bi-directionally, in which the value of the database and the item will be synchronized.
The group may also insert new rows instead of updating a specific row. In this manner, data can be inserted for historical purposes based on a timer, with an optional trigger.
The standard group uses a timer-based execution model shared by all groups, and the normal trigger settings.
Additionally, there are several settings specific to the group type:
| • | Automatically create table - If the target table does not exist, or does not have all of the required columns, it will be created/modified on group startup. If not selected and the table doesn't match, an error will be generated on startup. |
| • | Store timestamp - Specifies whether or not to store a timestamp with the record, and the target column. The timestamp will be generated by the group during execution. For groups that update a row, the timestamp will only be written if any of the values in the group is also written. |
| • | Store quality code - If selected, stores an aggregate quality for the group to the specified column. The aggregate quality is the combined quality of all of the items that write to the table. For more information about quality values, see Data Quality |
| • | Delete records older than - If selected, records in the target table will be deleted after they reach the specified age. This setting is useful for preventing tables from growing in an unbounded manner, which can cause disk space and performance problems over time. |
| • | Table action - This section details how the group interacts with the table. The group can insert a new row each execution, or update the first, last or custom record. A custom update clause is essentially the where clause of the SQL query that will be generated to read and write the group. In addition to standard SQL syntax, you can bind to items in the group in order to inject dynamic values. |
Standard groups can be used any time you want to work with a single row of data. This can include:
| • | Historical logging - set the group to insert new records, and log data historically either on a timer, or as the result of a trigger. Flexible trigger settings and handshakes make it possible to create robust transactions. |
| • | Maintain status tables - Keep a row in the database updated with the current status values. Once in the database, your process data is now available for use by any application that can access a database, dramatically opening up possibilities. |
| • | Manage recipes - Store recipe settings in the database, where you have a virtually unlimited amount of memory. Then, load them into the PLC by mapping DB-to-OPC using a custom where clause with an item binding in order to dynamically select the desired recipe. |
| • | Sync PLCs - Items in the group can be set to target other items, both for one-way and bi-directional syncing. By adding items from multiple PLCs to the group, you can set the items of one PLC to sync with the others. By creating expression items that map from one PLC item to the other, you can manipulate the value before passing it on. |
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