> ## Documentation Index > Fetch the complete documentation index at: https://docs.emergence.ai/llms.txt > Use this file to discover all available pages before exploring further. # Get a column by FQN > Get a specific column by its fully qualified name (FQN). The FQN format is: service.database.schema.table.column Example: PostgreSQL.dvdrental.public.customer.email Args: fqn: Fully qualified name of the column. ctx: Request context for authentication. service: Data assets service instance. Returns: Column domain model. Raises: HTTPException: 404 if column not found. ## OpenAPI ````yaml /openapi/em-data-readiness-v2.yaml get /api/data-readiness/data-assets/columns/by-fqn openapi: 3.1.0 info: title: EM Data Readiness Service description: Data Readiness Service API for managing workflows, metrics, and data quality version: 4.3.0-dev1 servers: [] security: - BearerAuth: [] tags: - name: Health description: Service health monitoring. Check service status and version information. - name: Root description: Root endpoint providing service information and navigation links. - name: Configuration description: Service configuration endpoints. View current configuration values. - name: Workflows description: >- Workflow configuration and execution management. Create, configure, and run data quality workflows including definitions, configurations, runs, and tasks. - name: Data Assets description: >- Data catalog entity management. Manage databases, schemas, and tables metadata. - name: Metrics description: >- Data quality metrics and scorecards. Calculate scores, view trends, and analyze dimensions. - name: Violations description: >- Data quality violation management. View, acknowledge, and remediate detected violations. - name: Glossary description: >- Business glossary management. Create, verify, and organize business terms and definitions. paths: /api/data-readiness/data-assets/columns/by-fqn: get: tags: - Data Assets summary: Get a column by FQN description: |- Get a specific column by its fully qualified name (FQN). The FQN format is: service.database.schema.table.column Example: PostgreSQL.dvdrental.public.customer.email Args: fqn: Fully qualified name of the column. ctx: Request context for authentication. service: Data assets service instance. Returns: Column domain model. Raises: HTTPException: 404 if column not found. operationId: get_column_by_fqn parameters: - name: fqn in: query required: true schema: type: string minLength: 1 description: >- Fully qualified name of the column (e.g., service.database.schema.table.column) title: Fqn description: >- Fully qualified name of the column (e.g., service.database.schema.table.column) responses: '200': description: Successful Response content: application/json: schema: $ref: '#/components/schemas/Column' '404': description: Column not found content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '422': description: Validation Error content: application/json: schema: $ref: '#/components/schemas/HTTPValidationError' '500': description: Internal Server Error content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' security: - BearerAuth: [] components: schemas: Column: properties: id: anyOf: - type: string - type: 'null' title: Id description: Unique column identifier (UUID) name: type: string title: Name description: Column name fqn: anyOf: - type: string - type: 'null' title: Fqn description: Fully qualified name data_type: anyOf: - type: string - type: 'null' title: Data Type description: SQL data type (e.g., VARCHAR(255), INTEGER, NUMERIC(15,2)) description: anyOf: - type: string - type: 'null' title: Description description: Technical description of the column display_name: anyOf: - type: string - type: 'null' title: Display Name description: User-friendly display name data_type_display: anyOf: - type: string - type: 'null' title: Data Type Display description: Human-readable data type description business_rules: anyOf: - type: string - type: 'null' title: Business Rules description: Business rules governing this column (max 1000 chars) business_definition: anyOf: - type: string - type: 'null' title: Business Definition description: Business meaning and purpose (max 1000 chars) summary_text: anyOf: - type: string - type: 'null' title: Summary Text description: Summary text for semantic search embedding constraint: anyOf: - additionalProperties: true type: object - type: 'null' title: Constraint description: >- Column constraint as structured JSONB (constraintType, referenceTable, etc.) column_relationships: anyOf: - items: additionalProperties: true type: object type: array - type: 'null' title: Column Relationships description: Relationships to other columns (FK references, etc.) tags: anyOf: - items: additionalProperties: true type: object type: array - type: 'null' title: Tags description: List of tag dicts with tagFQN, name, justification, etc. data_quality: anyOf: - items: additionalProperties: true type: object type: array - type: 'null' title: Data Quality description: DQ tags with nested rules and execution results type: object required: - name title: Column description: >- Column domain model for API responses and requests. Clean DTO representing a table column with comprehensive technical and business metadata. Supports business context enrichment through business_rules and business_definition fields. Used for nested column creation within tables. ErrorResponse: properties: error: $ref: '#/components/schemas/ErrorInfo' description: >- Error information object containing code, message, and optional details request_id: anyOf: - type: string - type: 'null' title: Request Id description: Request ID for debugging and support examples: - req_abc123xyz type: object required: - error title: ErrorResponse description: >- Standard error response model for API errors. Matches the structure returned by _handle_service_error in workflows/routes.py. The actual API response format is: { "error": { "code": "ERROR_CODE", "message": "Error message", "details": {...} }, "request_id": "optional-request-id" } HTTPValidationError: properties: detail: items: $ref: '#/components/schemas/ValidationError' type: array title: Detail type: object title: HTTPValidationError ErrorInfo: properties: code: type: string title: Code description: >- Error code identifier (e.g., 'WORKFLOW_NOT_FOUND', 'VALIDATION_ERROR') examples: - WORKFLOW_NOT_FOUND message: type: string title: Message description: Human-readable error message examples: - >- Workflow configuration with id '123e4567-e89b-12d3-a456-426614174000' not found details: anyOf: - additionalProperties: true type: object - type: 'null' title: Details description: >- Additional error details as a dictionary (flexible structure for business logic errors) examples: - workflow_id: 123e4567-e89b-12d3-a456-426614174000 type: object required: - code - message title: ErrorInfo description: >- Nested error information object. Note: This model uses an untyped dict for `details` to match the flexible error structure used throughout the service layer (see WorkflowServiceError and similar). This is distinct from ErrorDetail, which is used for structured validation errors. ValidationError: properties: loc: items: anyOf: - type: string - type: integer type: array title: Location msg: type: string title: Message type: type: string title: Error Type type: object required: - loc - msg - type title: ValidationError securitySchemes: BearerAuth: type: http scheme: bearer bearerFormat: JWT description: >- JWT Bearer token authentication. Include the token in the Authorization header as: `Authorization: Bearer `. The JWT must contain valid client_id, and project_id claims for tenant isolation and SDK routing. ````