Change a column’s type, converting every existing value. The column keeps its id and name. DescribeDatabase lists each column’s safeTypes (every value converts) and checkedTypes (each value is checked first). Any other type is refused while the column holds values; an empty column takes any type. If a value does not fit (“soon” as a number), or a multi-valued cell would lose values to a single-valued type, nothing changes and the error counts the misfits and quotes a few: fix them with UPDATE and retry, or add a new column. Clear values only when the user asked for that. - entity needs specificEntityType: USER makes a person column; DOCUMENT, TASK and the rest reference other Macro items. - linkToTableId (with dataType: entity) makes a relation to rows of another table of this database. Relations are always multi-valued, and the column must be empty. - Converting to select or tag turns the distinct existing values into options; options adds labels no row has yet. tag columns are always multi-valued. Requires edit access. The response is the schema after the change.