Data types for columns

Every row of the Column Mapping table has a Data Type box. The type you set there is the type each mapped value is converted to before it is written to the destination table.

This page covers what the box accepts. For the mapping itself, see Map columns. For the domains and their catalogue, see Data domains.

Set the data type

1. Open the Writeback table and select Columns.
2. In the row of the target column, find the Data Type box, next to the Source Columns choice. An empty box shows Select or type....
3. Pick a type from the list, or type the type you want.
4. Repeat this for the other rows. The type is saved with the rest of the mapping when you click Apply.

While you type, the list narrows to the types that match your text. When nothing matches, the list reads No matching data type. Your value is checked each time it changes, so a type DataMind OS does not recognise is marked in red straight away.

Which types are accepted

The box checks the whole value against the data type names DataMind OS knows:

• An empty or blank value is not accepted.
• The check ignores case, so datetime64(3) is treated the same as DateTime64(3).
• Sizes and parameters go in round brackets after the type, as in Decimal(10,2), DateTime64(3) or FixedString(50).
• Brackets are accepted for two groups of types only:
  • Types with number parameters: String, FixedString, Decimal, Decimal32, Decimal64, Decimal128, Decimal256, DateTime64, Enum8 and Enum16. Inside the brackets, write digits separated by commas.
  • Types that hold another type: DateTime, Array, LowCardinality, Tuple, Map, Nested and Variant. Inside the brackets, write the type they hold, as in LowCardinality(String), Tuple(Date, Date) or Map(String, String).
• Any other type takes no brackets.
• Empty brackets, as in Decimal(), do not pass.

Why a type is marked in red

A red Data Type blocks Apply while its column is not skipped. A column you skipped is not checked. Fix the box to unblock Apply.

What a run writes

• Each mapped value is converted to the type set in its row before it is written.
• The Data Type changes what your values are converted to. It does not change the column in the destination table.

Questions, answered

Which data types can I enter?

A data type name such as String, Int32, Date, Bool or Decimal(10,2). The whole value must match a type DataMind OS knows, and case is ignored.

Can I type a data type that is not in the list?

Yes. The list is a set of suggestions. A type you type in is accepted as long as the whole value matches a type DataMind OS knows. Anything else is marked in red.

Is the data type check case-sensitive?

No. The comparison ignores case, so datetime64(3) is treated the same as DateTime64(3).

How do I add a size or parameters to a type?

Write them in round brackets after the type: Decimal(10,2), DateTime64(3) or FixedString(50). Brackets are accepted only for the types in the two groups under Which types are accepted: digits separated by commas for the number-parameter types, and a held type for types such as LowCardinality(String). Other types take no brackets, and empty brackets are not accepted.

Why is my data type marked in red?

The box is empty or blank, or the value is not a data type name DataMind OS knows. An empty box shows Please select data type; an unrecognised value shows Invalid data type. While the column is not skipped, Apply stays blocked until you fix the box.

Why does the list say "No matching data type"?

The list filters to the text you have typed and found no suggestion for it. Finish typing your type, or pick one from the list. What you type is checked each time it changes.

Can each column have its own data type?

Yes. The Data Type box belongs to a single mapping row, so every target column carries its own type.