4.3 Creating and Modifying Columns

Columns are where data modeling gets granular, and AB-410 tests both the limits and the 'which type do you pick' judgment calls. Add columns from the table hub's Columns area or directly in the data workspace.

Display Name versus Schema Name

Every column has a display name (editable later) and a schema name (locked at save, carrying the publisher prefix such as contoso_). Flows, formulas, and API calls reference the schema name, so renaming a display name is safe — but you can never rename the schema name.

Text Columns

Reducing a maximum length later does not truncate existing data — the new limit applies only to new rows.

Numbers: Whole, Decimal, Float, Currency

• Whole number — integers from -2,147,483,648 to 2,147,483,647, with formats such as Duration, Time Zone, and Language
• Decimal — stored exactly as entered, up to 10 decimal places; pick it for precise financial calculations and equality comparisons
• Floating point — stores an approximation with up to 5 decimal places; faster, fine for measurements compared with greater-than/less-than
• Currency — money values with precision of 0 to 4, or the organization's Pricing Decimal Precision, or Currency Precision per row; adding the first currency column to a table also creates a Currency lookup, an Exchange Rate column, and a _Base column holding the base-currency conversion

Date and Time Behaviors — the Big Exam Trap

If a traveling user must always see the same calendar date, User Local is wrong because a stored UTC value can render as the previous or next day in another zone.

Choice, Choices, and Yes/No

• Choice — one value from a list; Choices (multi-select) allows several. Multi-select choices cannot be used in workflows, business process flows, business rules, charts, or rollup and calculated columns
• Local vs global: a local choice lives on one column; a global choice is a reusable list shared across tables and columns — use global when the same list (for example, Region) appears in many places so it stays consistent
• Yes/No — a boolean with two customizable labels (for example, Approved / Rejected)

Decision shortcut the exam loves: pick Yes/No for exactly two states, Choice for a short, stable list, Lookup when values need their own rows, security, or columns — a choice cannot store 'which manager owns this region.'

Lookup and Customer

Creating a lookup column creates a many-to-one (N:1) relationship to a single target table. The Customer type is a special system lookup pointing to either an Account or a Contact — you cannot retarget it to other tables, and Customer is always searchable.

File, Image, and Autonumber

• File — binary documents; default maximum 32 MB, settable up to 131,072 KB (131 MB), and the limit cannot be changed after save. Required-field validation does not work on file columns, and in model-driven apps uploads and deletes happen immediately rather than on form save
• Image — one primary image per table; default maximum 10,240 KB, up to 30,720 KB; uploads are resized to a 144 x 144 pixel thumbnail for display and cropped square; jpg, jpeg, gif, bmp, and png are accepted
• Autonumber — auto-generated values with string prefixed, date prefixed, or custom seed formats; remember it cannot be created in the data workspace

Required Levels and the Searchable Flag

• Optional — no constraint
• Business recommended — a soft nudge; the form shows a blue plus indicator but saves anyway
• Business required — hard validation; the row cannot save without a value

Two finer points round out the picture. Precision settings matter on exams: decimal supports up to 10 decimal places, float up to 5, and currency 0 to 4 — and if you choose Currency Precision, a row priced in Japanese yen shows zero decimals while a US dollar row shows two, from the same column. Maximum length changes are non-destructive: shrinking a 4,000-character text column to 500 never truncates existing rows; it only constrains new data. Finally, a scenario that locks in the choice-versus-lookup trap: Northwind stores Region as a global choice shared by the Account and Site tables; when leadership later asks to track a regional manager and budget per region, a choice cannot carry that extra data — the maker models Region as its own table and switches to a lookup.

Almost every type is Searchable by default — flip it off for columns that pollute quick-find results. Images, formula columns, and party-list lookups cannot be searched at all.

Looking Ahead

You will also see calculated, rollup, and formula (Power Fx) columns listed as data types. For this chapter, just recognize that they exist and that they compute values rather than store entered data — Chapter 16 covers building them in depth.