When character values are mixed with integer values in a data set column, it is best described as an issue of invalid data type. A data set column typically requires a consistent data type (either all integers or all characters) to ensure proper functionality during data analysis and processing. Mixing different data types in the same column can cause errors and complications since the software may not be able to perform operations correctly on mixed data types.

ETL (Extract, Transform, Load) is a process used during data integration to collect, blend, and load data. The process involves extracting data from multiple sources, transforming it into a format suitable for analysis, and then loading it into a target system, such as a data warehouse. This is a standard procedure for integrating and preparing data for reporting and analysis.

After confirming the data sources and creating a wireframe for the internal user dashboard, the next step should be to get stakeholder approval. This ensures that the design and structure meet the expectations and requirements of those who will use the dashboard. Stakeholder feedback is crucial before moving forward, as it allows for any necessary adjustments to be made to the wireframe before further development or deployment occurs.

To derive a new variable like 'Promotion_flag' based on whether the quantity sold by each salesperson is above a specified threshold (1,000,000 in this case), logical functions are appropriate. Logical functions allow making decisions based on conditions. For example, using an IF statement to check if the Quantity_sold is greater than 1,000,000 and then flagging 'Yes' or 'No' accordingly. Other function types such as Date, Mathematical, and Aggregate are not specifically suited for creating conditional flags based on criteria.

The diagram represents a relational database schema. In a relational database, data is organized into tables (or relations) that are connected to each other by relationships, typically using foreign keys. The diagram shows tables such as Runs, Experiments, and RunValues, each with distinct columns and connected through keys, which is characteristic of a relational database structure.