-- Migration: Add usage_description column to metadata_field_definitions table
-- [AC-IDSMETA-XX] Add usage description field for metadata field definitions

-- Add usage_description column
ALTER TABLE metadata_field_definitions
ADD COLUMN IF NOT EXISTS usage_description TEXT;

-- Add comment
COMMENT ON COLUMN metadata_field_definitions.usage_description IS '用途说明，描述该元数据字段的业务用途';
