Connect To and Transform Data24% of the exam
Tableau Prep unions, joins and aggregations
Pick the Tableau Prep step a business need calls for, then configure it: Union steps and Input-step unions with mismatched fields and type conflicts, Join steps with seven join types and join-clause cleaning, Aggregate steps with grouped versus aggregated fields, and FIXED LOD calculations that keep row detail.
Perform data transformation in Tableau Prep: Choose which data transformation to perform based on a business scenario; Combine data by using unions; Combine data by using joins; Shape data by using aggregations; Perform filtering; Shape data by using pivots; Determine which output type to use.
~7 min read · 11 practice questions ·
What the exam expects
- Choose the Prep transformation a scenario needs: union, join, aggregate, FIXED LOD or pivot.
- Union in a Union step or the Input step, and fix mismatched fields and type conflicts.
- Join with the right join type, read the join results and clean values that fail to match.
- Aggregate, and know whether a filter runs before or after the aggregation.
- Prep filtering, the Pivot step and output types are taught in Tableau Prep filters, pivots and output types; Desktop joins and unions in Relationships, joins, unions and data source filters.
Key terms:
- Union: appends the rows of one table onto another.
- Join: combines related tables on common fields, typically extending the table horizontally.
- Granularity: what one row represents, such as one row per room per day.
- Grouped / Aggregated Fields: the fields that make the row, and the data summarized at that level.
- Mismatched field: a field that did not line up across a union's tables.
Key facts
Union requirements
- Detail
- Same number of fields, field names and data types
Union step inputs
- Detail
- Maximum of 10; union more in the Input step
Input-step union
- Detail
- Same directory or sub-directory; not for Tableau extracts
Wrong merged type
- Detail
- Separate Inputs with Different Types, change one, merge again
Join defaults
- Detail
- Inner join; first clause from common field names
Aggregate filters
- Detail
- Grouped field: before aggregation; aggregated field: after
Prep LOD support
- Detail
- FIXED only; no combining with another expression
Sources for this section (4)
- Why can't you fix a data type in the Output step?
- When is an Input-step union unavailable?
- What do the right table's fields show in a leftOnly join?
The questions are free to read. Answers with their sources and self-grading are included with the pack.
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