.alter-merge table command
Applies to: ✅ Microsoft Fabric ✅ Azure Data Explorer
The .alter-merge table command:
- Secures data in existing columns
- Adds new columns,
docstring, and folder to an existing table - Must run in the context of a specific database that scopes the table name
Permissions
You must have at least Table Admin permissions to run this command.
Syntax
.alter-merge table tableName (columnName:columnType [, ...]) [with (propertyName = propertyValue [, ...])]
Learn more about syntax conventions.
Parameters
| Name | Type | Required | Description |
|---|---|---|---|
| tableName | string |
✔️ | The name of the table to alter. |
| columnName, columnType | string |
✔️ | The name of an existing or new column mapped to the type of data in that column. The list of these mappings defines the output column schema. |
| propertyName, propertyValue | string |
A comma-separated list of key-value property pairs. See supported properties. |
Note
If you try to alter a column type, the command will fail. Use .alter column instead.
Tip
Use .show table [tableName] cslschema to get the existing column schema before you alter it.
Supported properties
| Name | Type | Description |
|---|---|---|
docstring |
string |
Free text describing the entity to be added. This string is presented in various UX settings next to the entity names. |
folder |
string |
The name of the folder to add to the table. |
How the command affects the data
- Existing data won't be modified or deleted
- New columns will be added to the end of the schema
- Data in new columns is assumed to be null
Examples
.alter-merge table MyTable (ColumnX:string, ColumnY:int)
.alter-merge table MyTable (ColumnX:string, ColumnY:int) with (docstring = "Some documentation", folder = "Folder1")
Related content
Use the .alter table command when you wish to further redefine the table settings. For more information, see .alter table.