The terms "simple", "primitive", and "elementary" data types are used synonymously.

Numeric types

DyNumber | A binary representation of a real number with an accuracy of up to 38 digits.
Acceptable values: positive numbers from 1×10^-130 up to 1×10¹²⁶–1, negative numbers from -1×10¹²⁶–1 to -1×10^-130, and 0.
Compatible with the Number type in AWS DynamoDB. It's not recommended for ydb-native applications. |

String types

Unlike the JSON data type that stores the original text representation passed by the user, JsonDocument uses an indexed binary representation. An important difference from the point of view of semantics is that JsonDocument doesn't preserve formatting, the order of keys in objects, or their duplicates.

Thanks to the indexed view, JsonDocument lets you bypass the document model using JsonPath without the need to parse the full content. This helps efficiently perform operations from the JSON API, reducing delays and cost of user queries. Execution of JsonDocument queries can be up to several times more efficient depending on the type of load.

Due to the added redundancy, JsonDocument is less effective in storage. The additional storage overhead depends on the specific content, but is 20-30% of the original volume on average. Saving data in JsonDocument format requires additional conversion from the textual representation, which makes writing it less efficient. However, for most read-intensive scenarios that involve processing data from JSON, this data type is preferred and recommended.

Date and time

Supporting types with a time zone label

Time zone label for the TzDate, TzDatetime, TzTimestamp types is an attribute that is used:

• When converting (CAST, DateTime::Parse, DateTime::Format) to a string and from a string.
• In DateTime::Split, a timezone component is added to Resource<TM>.

The point in time for these types is stored in UTC, and the timezone label doesn't participate in any other calculations in any way. For example:

select --these expressions are always true for any timezones:  the timezone doesn't affect the point in time.
    AddTimezone(CurrentUtcDate(), "Europe/Moscow") ==
        AddTimezone(CurrentUtcDate(), "America/New_York"),
    AddTimezone(CurrentUtcDatetime(), "Europe/Moscow") == 
        AddTimezone(CurrentUtcDatetime(), "America/New_York");

Keep in mind that when converting between TzDate and TzDatetime, or TzTimestamp the date's midnight doesn't follow the local time zone, but midnight in UTC for the date in UTC.

Casting between data types

Explicit casting

Explicit casting using CAST:

Casting to numeric types

¹ True is converted to 1 and False to 0.
² Any value other than 0 is converted to True, 0 is converted to False.
³ Possible only in the case of a non-negative value.
⁴ Using the built-in function Yson::ConvertTo.

Converting to date and time data types

Conversion to other data types

⁴ Using the built-in function Yson::ConvertTo.

Examples

SELECT
CAST("12345" AS Double), -- 12345.0
CAST(1.2345 AS Uint8), -- 1
CAST(12345 AS String), -- "12345"
CAST("1.2345" AS Decimal(5, 2)), -- 1.23
CAST("xyz" AS Uint64) IS NULL, -- true, because it failed
CAST(-1 AS Uint16) IS NULL, -- true, a negative integer cast to an unsigned integer
CAST([-1, 0, 1] AS List<Uint8?>), -- [null, 0, 1]
--The item type is optional: the failed item is cast to null.
CAST(["3.14", "bad", "42"] AS List), -- [3.14, 42]
--The item type is not optional: the failed item has been deleted.
CAST(255 AS Uint8), -- 255
CAST(256 AS Uint8) IS NULL -- true, out of range

Implicit casting

Implicit type casting that occurs in basic operations ( +-*/) between different data types. The table cells specify the operation result type, if the operation is possible:

Numeric types

Date and time types