====== Data Operation - Comparison (Diff) ======


===== About =====
A ''compare'' is a [[op|data operation]] that will search and show difference between [[docs:resource:resource|data resources]].

The ''comparison'' may be performed:
  * at the [[docs:resource:metadata|metadata level]], meaning
      * on the [[docs:resource:attribute|data resource attributes]]
      * on the [[docs:resource:structure|data structure]]
  * or and at the data level record by record



<note>
Howto: [[howto:getting_started:10_resource_comparison]]
</note>


===== Command and Arguments =====

The ''compare'' operation is supported by the [[docs:tabli:data:compare|data compare command]]
==== Data Selector (Source) ====
The [[docs:resource:data_selector|data selector]] can choose any [[docs:resource:content|content resource]] such as:
  * [[docs:resource:table|table]]
  * [[docs:resource:query|query]]
  * [[docs:resource:file|file]]
==== Target Uri ====

  * The [[docs:resource:target_uri|target uri]] may be not given as argument. If this is the case, the comparison will except an empty target.

==== Report Level ====
The ''report-level'' argument defines what the command will return:
  * ''resource'' - a comparison report will be created for all comparison
  * ''record'' - a comparison report will be created for each comparison and the record data comparison will be available
  * ''all'' - all type of comparison report will be created

==== Data Source ====
The ''data-source'' defines the origin of the data to compare.
  * ''content'' - the default - the data to compare will be the records
  * ''structure'' - the data to compare will be the column definitions.

==== Unique Columns / Driver Columns ====
The ''unique columns (driver columns)'' are the columns that drives the comparison process.

For instance, if you compare two resources that have an unique id column,
  * if the comparison has fetched:
      * a source record with a id value of ''1''
      * a target record with a id value of ''2''
  * the comparator will:
      * mark the source record has missing in the target
      * fetch records only from the source until it finds the record with the id ''2'' or above.