# excel_datamodel - Server Quirks
**PREREQUISITE: Tables must be added to Data Model first!**
The Data Model (Power Pivot) only contains tables that were explicitly added.
You CANNOT create DAX measures on tables that aren't in the Data Model.
**How to add tables to the Data Model**:
| Source | Method |
|--------|--------|
| Worksheet Excel Table | excel_table with add-to-datamodel action |
| External file (CSV, etc.) | excel_powerquery with loadDestination='data-model' |
| Database/web source | excel_powerquery with loadDestination='data-model' |
**Action disambiguation**:
- list-tables: List all tables currently in the Data Model
- list-measures: List all DAX measures in the Data Model
- create-measure: Create a new DAX measure (requires tableName, measureName, daxFormula)
- update-measure: Modify existing measure's formula/format/description
- delete-measure: Remove a measure
- delete-table: Remove table AND ALL its measures (DESTRUCTIVE!)
- read-info: Get Data Model metadata (culture, compatibility level)
- refresh: Refresh all Data Model data from sources
**DAX measure creation**:
- tableName: Which table the measure belongs to (for organization)
- measureName: Display name for the measure
- daxFormula: DAX expression (e.g., "SUM(Sales[Revenue])")
- formatString: Optional number format (#,##0.00, 0%, $#,##0, etc.)
**Common DAX patterns**:
```dax
// Sum
SUM(TableName[ColumnName])
// Average
AVERAGE(TableName[ColumnName])
// Count rows
COUNTROWS(TableName)
// Calculated ratio
DIVIDE(SUM(Sales[Revenue]), SUM(Sales[Units]), 0)
```
**Common mistakes**:
- Creating measures before adding source table to Data Model → Error
- Using worksheet table names instead of Data Model table names
- Forgetting that delete-table removes ALL measures on that table
- Not specifying tableName when creating measures (required for organization)
**Server-specific quirks**:
- 2-minute auto-timeout on Data Model operations
- Table names in Data Model may differ from worksheet (check list-tables)
- Refresh refreshes ALL tables, not individual ones
- Measure names must be unique across entire Data Model (not per-table)
