Generally, all fields in a data source have a data type. The data type identifies the kind of information contained in such fields, for example; integer (123), date (23/12/2020) or Boolean (T/F).
Anytime you connect a new data source in Tableau. Tableau assigns each field in your data sources a specific data type. These data types can be identified using the icons appended right before each field name on the data pane.
Not all data types will be interpreted correctly by Tableau. Sometimes a date type might be interpreted as a string, or an integer as a string. In such cases, you can re-assign the correct data type by clicking the fields data type icon and choosing the correct data type or simply right clicking the field you need to reassign >> Change Data Type >> choose the correct data type.
Note: All calculations you create in Tableau, will bear an equal sign before the data type icon. For example, an integer calculations (=#), a string calculation (=Abc), a Boolean calculation (=T/F) etc.
In addition to data types, Tableau also assigns data roles which determine on how fields behave when added to the shelves. In Tableau every fields is either assigned as dimension or measure, or a discrete or continuous field.
Dimension fields contain qualitative values (such as dates, names or geographical fields). When added to the shelves, they either categorize, segment or reveal the details in your data.
Measure fields contains quantitative values (measures can be aggregated). When added to the shelves, Tableau applies aggregation by default.
Note that when a field is added to the shelves – Tableau represents the data differently depending on whether the field is a continuous (green) or a discrete (blue) field. See example below;
Data types and roles play a crucial part in helping you understand the kind of data contained in fields and determine how such data will be used in visualizations.
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