# Dax Authoring

> Write and test DAX queries against Power BI semantic models. Covers DAX syntax rules, query patterns, time intelligence, and an iterative test workflow using the Fabric CLI query command.

- Skill: `microsoft/dax-authoring` (Agent Skill, multi-file: 4 files)
- Install (CLI): `npx skillmds@latest add microsoft/dax-authoring`
- Raw SKILL.md: https://api.skillmd.com/api/skills/microsoft/dax-authoring/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Productivity
- Author: Microsoft (https://skillmd.com/u/microsoft)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/microsoft/dax-authoring

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# DAX Authoring

## Table of Contents

| Task | Reference | Notes |
|---|---|---|
| Must/Prefer/Avoid | [SKILL.md: Must/Prefer/Avoid](#must--prefer--avoid) | Guardrails for DAX query generation |
| Generating DAX Queries | [SKILL.md: Generating DAX Queries](#generating-dax-queries) | Core rules, inline examples, EVALUATE/DEFINE patterns |
| DAX Query Structure & Syntax | [dax-query-patterns.md: Query Structure](./references/dax-query-patterns.md#query-structure) | DEFINE / EVALUATE / ORDER BY / START AT |
| DAX Query Key Components | [dax-query-patterns.md: Key Components](./references/dax-query-patterns.md#key-components) | DEFINE VAR, DEFINE MEASURE, table expressions |
| DAX Query Worked Examples | [dax-query-patterns.md: Common Patterns](./references/dax-query-patterns.md#common-patterns) | 11 annotated examples from simple aggregation to cross-table joins |
| DAX Query Anti-Patterns | [dax-query-patterns.md: Anti-Patterns](./references/dax-query-patterns.md#anti-patterns) | What to avoid in DAX queries |
| CALCULATE & CALCULATETABLE | [dax-core-reference.md: CALCULATE & CALCULATETABLE](./references/dax-core-reference.md#calculate--calculatetable) | Context transition, filter types, boolean restrictions, common patterns |
| SUMMARIZECOLUMNS | [dax-core-reference.md: SUMMARIZECOLUMNS](./references/dax-core-reference.md#summarizecolumns) | Argument order, auto-blank elimination, filter args, vs SUMMARIZE |
| ALL & ALLEXCEPT | [dax-core-reference.md: ALL & ALLEXCEPT](./references/dax-core-reference.md#all--allexcept) | CALCULATE modifier vs table function; percentage patterns |
| TREATAS | [dax-core-reference.md: TREATAS](./references/dax-core-reference.md#treatas) | Virtual relationships, multi-column filtering |
| DAX Syntax Rules | [dax-core-reference.md: DAX Syntax Rules](./references/dax-core-reference.md#dax-syntax-rules) | EVALUATE, CALCULATE, naming, SQL keywords, DEFINE rules |
| Common Mistakes | [dax-core-reference.md: Common Mistakes](./references/dax-core-reference.md#common-mistakes) | Variable naming, quoting, escaping, scalar EVALUATE, multi-table SUMMARIZECOLUMNS |
| BLANK Semantics | [dax-core-reference.md: BLANK Semantics](./references/dax-core-reference.md#blank-semantics) | BLANK vs NULL, propagation, equality, ISBLANK, DIVIDE, non-empty semantics |
| Time Intelligence Patterns | [SKILL.md: Time Intelligence](#time-intelligence) | When to consult TI reference |
| Date Table Prerequisites | [dax-time-intelligence.md: Prerequisites](./references/dax-time-intelligence.md#prerequisites) | Date table requirements, mark as date table |
| YTD / QTD / MTD | [dax-time-intelligence.md: Period-to-Date](./references/dax-time-intelligence.md#period-to-date) | TOTALYTD, DATESYTD, DATESINPERIOD patterns |
| Year-over-Year / Period Comparisons | [dax-time-intelligence.md: Period Comparisons](./references/dax-time-intelligence.md#period-comparisons) | SAMEPERIODLASTYEAR, DATEADD, PARALLELPERIOD |
| Rolling Windows | [dax-time-intelligence.md: Rolling Windows](./references/dax-time-intelligence.md#rolling-windows) | DATESINPERIOD rolling 12-month patterns |
| Opening/Closing Balances | [dax-time-intelligence.md: Balances](./references/dax-time-intelligence.md#balances) | Semi-additive measures, LASTDATE, LASTNONBLANK |
| TI in DAX Queries (Critical Rules) | [dax-time-intelligence.md: Critical Rules for TI in Queries](./references/dax-time-intelligence.md#critical-rules-for-ti-in-dax-queries) | CALCULATETABLE + TREATAS pattern for query context |
| TI Common Mistakes | [dax-time-intelligence.md: Common Mistakes](./references/dax-time-intelligence.md#common-mistakes) | Missing date table, wrong granularity, fiscal calendar |
| Testing & Iteration | [SKILL.md: Testing & Iteration](#testing--iteration) | Execute → inspect → fix → re-test workflow |

## Must / Prefer / Avoid

### Must
- Always test generated DAX via `npx fabric-app-data query <alias> --query '<DAX>'` before using in app code
- Use fully-qualified `'Table'[Column]` for column references
- Use simple `[Measure]` for measure references
- Use DEFINE for VAR and local MEASURE declarations (single DEFINE block, no commas)
- Prefer existing model measures over re-aggregating raw data

### Prefer
- SUMMARIZECOLUMNS as the primary grouping function for queries
- TREATAS for filter arguments in SUMMARIZECOLUMNS
- Variables (VAR) to improve readability and avoid repeated calculations

### Avoid
- SQL keywords (SELECT, WHERE, HAVING, etc.) within DAX expressions
- EVALUATE with scalar functions directly (wrap in ROW or table function)

## Generating DAX Queries

### DAX Syntax Rules

- Measures are named objects in the semantic model. They specify how to aggregate data. **Measures should be used first** to answer user requests before a new DAX formula is used to aggregate data.
- **EVALUATE Statement**: Not a function but a statement. It must always precede a table expression. Avoid pairing EVALUATE with scalar functions like CONCATENATEX, SUMX, DISTINCTCOUNT, etc.
- Use the fully-qualified name `'Table'[Column]` for column references, and the simple name `[Measure]` for measure references.
- CALCULATE takes a scalar expression as its first argument. CALCULATETABLE takes a table expression as its first argument.
- SUMMARIZECOLUMNS requires a specific order: groupby columns, then filters, then aggregations/measures.
- Do not use SUMMARIZECOLUMNS when there is no aggregation and the groupby columns belong to more than one table; use VALUES, SUMMARIZE, or SELECTCOLUMNS instead.
- When using SELECTCOLUMNS or CALCULATETABLE, include any columns needed downstream (ORDER BY, FILTER).
- Filters propagate across relationships based on unidirectional or bidirectional settings.
- INTERSECT, UNION, EXCEPT require identical column counts in both inputs.
- For current date/time, use TODAY() or NOW().

### Inline Examples

**Simple filtered aggregation:**
```dax
// Total sales for red products
EVALUATE
  ROW("Total Sales Amount", CALCULATE([Total Amount], 'Product'[Color] == "Red"))
```

**Multi-filter grouping with SUMMARIZECOLUMNS:**
```dax
DEFINE
  VAR _Filter1 = TREATAS({"Consumer Electronics"}, 'Product'[Category])
  VAR _Filter2 = FILTER(ALL('Calendar'[Year]), 'Calendar'[Year] >= 2022 && 'Calendar'[Year] <= 2023)

EVALUATE
  SUMMARIZECOLUMNS(
    'Calendar'[Year],
    'Calendar'[Month],
    _Filter1,
    _Filter2,
    "Total Quantity", SUM('Sales'[Order Quantity]),
    "Discount", [Total Discount]
  )
```

**TopN with filtering:**
```dax
DEFINE
  VAR _Filter = TREATAS({"Red", "Black"}, 'Product'[Color])
  VAR _Core = SUMMARIZECOLUMNS('Product'[Name], _Filter, "Total Sales", [Total Amount])

EVALUATE
  TOPN(10, _Core, [Total Sales], DESC)
```

For full syntax reference, worked examples, and anti-patterns, see [dax-query-patterns.md](./references/dax-query-patterns.md).
For function details, see [dax-core-reference.md](./references/dax-core-reference.md).

## Time Intelligence

Time intelligence functions enable period-based analysis (YTD, YoY, rolling windows, etc.). They require a properly configured Date table.

Consult [dax-time-intelligence.md](./references/dax-time-intelligence.md) whenever the user's request involves:
- Period-to-date calculations (YTD, QTD, MTD)
- Period comparisons (Year-over-Year, Month-over-Month)
- Rolling windows (last 12 months, last 30 days)
- Opening/closing balances
- Custom date ranges

## Testing & Iteration

1. Generate the DAX query expression
2. Execute via `npx fabric-app-data query <alias> --query '<DAX>'`
3. Inspect results: check column names, data types, row counts, and actual data values
4. If error: consult [dax-core-reference.md](./references/dax-core-reference.md), fix, and re-test
5. Iterate until the query returns expected results

## Query Execution

Use `npx fabric-app-data query <alias> --query '<DAX>'` to run queries. This uses the same SDK pipeline as the running app, so results are identical to what the app produces at runtime. To re-test an existing `.dax` file without copying the query text, use `--file`: `npx fabric-app-data query <alias> --file src/queries/revenue.dax`. For full CLI options (profiles, result limits), see the `fabric-cli` skill.

**Result trimming:** The CLI returns at most 1000 rows by default. When the result is trimmed, the output includes a `_cliWarning` field (e.g., `"Result trimmed to first 1000 of 5000 rows"`). This is a CLI-only limitation — the full dataset is available in the running app. If you need to see more data, refine your DAX with filters or aggregations.

## Troubleshooting

| Problem | Solution |
|---------|----------|
| CLI `query` fails with "not signed in" | Run `az login` to sign in to Azure CLI |
| CLI `query` fails with "Azure CLI is not installed" | Install from https://aka.ms/install-azure-cli |
| CLI `query` fails with "alias not found" | Run `npx fabric-app-data list` to check available aliases, then `npx fabric-app-data add` to register |
| DAX syntax errors | Consult [dax-core-reference.md](./references/dax-core-reference.md) — check reserved keywords, quoting rules, EVALUATE/scalar mistakes |
| Unexpected query results | Check filter context, relationship direction, BLANK handling in [dax-core-reference.md](./references/dax-core-reference.md#blank-semantics) |
| Time intelligence returns wrong values | Check date table prerequisites and critical rules in [dax-time-intelligence.md](./references/dax-time-intelligence.md) |