Connecting to and Preparing Data23% of the exam
Join types and unions in the physical layer
How to open a logical table to reach the join canvas, what inner, left, right and full outer joins keep, and how manual and wildcard unions stack same-structure tables, including Merge Mismatched Fields and the Sheet and Table Name fields a union adds.
Create and manage the data model: Add relationships to a data source; Add joins and unions; Explain when to use a join versus a relationship.
~8 min read · 5 practice questions ·
What the exam expects
- Open a logical table to reach the join canvas and add a join with a join clause and a join type.
- Predict which rows inner, left, right and full outer joins keep, and where nulls appear.
- Union tables with the same structure, manually or with a wildcard pattern that picks up new tables.
- Fix a union whose field names don't match, and use the Sheet and Table Name fields a union generates.
- Key terms: join clause (the matching fields and operator, usually =); join type (inner, left, right or full outer); union (appends rows from tables with the same columns); wildcard union (includes every table whose name matches a pattern with
*); Merge Mismatched Fields (replaces non-matching union columns with one field).
Key facts
Reach the join canvas
- Detail
- Double-click a logical table or select Open
Join types
- Detail
- Inner, left, right, full outer
Inner join
- Detail
- Unmatched values are dropped entirely
Left join
- Detail
- All left values; null where the right table has no match
Multiple join clauses
- Detail
- All must be true for rows to join
Type change after joining
- Detail
- Breaks the join
Union requirement
- Detail
- Same connection; ideally same fields, names and types
Wildcard character
- Detail
*in the Include search criteria
Union field matching
- Detail
- By field name
Merge mismatched fields
- Detail
- One field with the first non-null value per row
Union-generated fields
- Detail
- Sheet and Table Name; usable as join keys
Sources for this section (2)
- Why does a union of tables with different column names show many nulls?
- When should you choose a full outer join?
- Why can changing a join field's data type cause trouble?
- Where does the option to set up a union appear?
The questions are free to read. Answers with their sources and self-grading are included with the pack.
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