Data types

This section describes the data types supported by YTsaurus and the way they are described in the schema and represented in the formats.

Overview

YTsaurus supports a number of primitive types:

• string;
• integer;
• boolean;
• float;
• double;
• date;
• datetime;
• timestamp;
• interval.

As well as the following composite (complex) types:

• optional;
• list;
• struct;
• tuple;
• variant;
• tagged.

You can use one of the following two methods to specify a type in a table schema:

• Using the type and (optionally) the required keys: historically, the first method but it is only good for defining primitive or optional primitive types.
• Using the type_v3 key.

The type key always expects a string.
The type_v3 key expects either a string for primitive types or a YSON dictionary.
A yson dict always has the type_name key that stores the type name.
The remaining keys depend on the specific type and are described below.

Describing types in a schema

Primitive types

You can define primitive types in a schema both using the type and the type_v3 keys.

If primitive type T is defined using type, YTsaurus will additionally check the required key in the schema:

• required=%true: the column will have a strictly defined type. Null or empty values are illegal.
• required=%false: the column will be of type optional<T>. Any values of a primitive type and the Null value will be legal.

The table lists the supported types and their representation in the type/type_v3 keys.

Schema example:

type_v3=utf8

type_v3=bool

type_v3=yson

Decimal

The values of type decimal(p, s) are real numbers with the specified precision.

To define this type in a schema, specify the following keys:

• type_name: value of decimal.
• precision: total number of decimal digits in the representation of a number, precision must be in the range [1, 35].
• scale: number of digits to the right of the decimal point in the representation of a number, scale must be in the range [0, precision].

Schema example:

type_v3={
    type_name=`decimal`
    precision=10;
    scale=2;
}

The values 3.14, -2.71, 9.99 may be of type decimal(3, 2) (precision=3, scale=2).

The type supports a number of special values, such as nan, +inf, -inf.

Description of binary representation

There is a special binary representation of decimal numbers,
that many formats like yson use by default.

For the purposes of this representation, the values of decimal(p, s) types are maintained as binary strings. Binary string length
depends on precision.

You need to perform the following steps to obtain a binary representation of a decimal number. These steps will be illustrated with the values 3.1415, -2.7182 of type decimal(5, 4).

1. Take an integer made up of the value's digits. The number of bits is taken from precision in the table above. In this example, 32-bit numbers 31415, -27182.
2. Write the number as a big-endian sequence. In this example, the strings are \x00\x00\x7A\xB7, \xFF\xFF\x95\xD2.
3. Invert the most significant bit. In this example, the strings are \x80\x00\7A\xB7, \x7F\xFF\x95\xD2.

The integer representations of the special values of nan, +inf, -inf for the first step are shown in the table below:

Optional type

The optional<T> type means that a value may be of type T or be empty.

Legacy columns containing the type=T;required=false attributes correspond to type optional<T> defined using type_v3.

To define type optional, specify the keys below:

• type_name: value of optional.
• item: element type description.

Schema example:

type_v3={
  type_name=optional;
  item=string;
}

type_v3={
  type_name=optional;
  item={
    type_name=optional;
    item=bool;
  }
}

List

Values of type list<T> are lists of elements of type T.

To define the type in the schema, specify the keys below:

• type_name: value of list.
• item: element type description.

Schema example:

type_v3={
  type_name=list;
  item=string;
}

type_v3={
  type_name=list;
  item={
    type_name=list;
    item=double;
  }
}

Struct

A collection of named fields with specified value types.

To define this type in a schema, specify the following keys:

• type_name: value of struct.
• members: list of dictionaries with keys:
  • name: field name, must be a non-empty utf8 string.
  • type: field type.

Schema example:

type_v3={
  type_name=struct;
  members=[
    {
      name=foo;
      type=int32;
    };
    {
      name=bar;
      type={
        type_name=optional;
        item=string;
      }
    };   
  ]
}

Tuple

A collection of unnamed fields of certain predefined types.

To define this type, you need to specify the following keys in the schema:

• type_name: value of tuple.
• elements: list of dictionaries with keys:
• type: element type.

Schema example:

type_v3={
  type_name=tuple;
  elements=[
     {
       type=double;
     };
     {
       type=double;
     };
  ]
}

Variant

Variant is strictly a single value from a defined collection of types.
A variant may be of one of two types:

• Variant over struct. Each type has a name (as in a struct), and each variant value is labeled with the name of the relevant variant element value.
• Variant over tuple. In this case, all the elements are unnamed, and each value is labeled with an index.

To define this type, specify the following keys in a schema:

• type_name: value of variant.
• elements or members (not both): the keys have the same structure similar as these keys in tuple / struct:

• elements: for the option with unnamed elements with the key itself containing a list of dictionaries with keys:
  • type: element type.
• members: for the option with named elements with the key itself containing a list of dictionaries with keys:
  • name: element name, must be a non-empty utf8 string.
  • type: description of element type.

Schema example:

type_v3={
  type_name=variant;
  members=[
     {
       name=int_field;
       type=int64;
     };
     {
       name=string_field;
       type=string;
     };
  ]
}

type_v3={
  type_name=variant;
  elements=[
     {
       type=int32;
     };
     {
       type=string;
     };
     {
       type=double;
     };
  ]
}

Dict

A dict is a sequence of key/value pairs.
YTsaurus does not check the keys for uniqueness or order.
However, most clients will upload data to an actual dictionary while processing, and the value for non-unique keys will be lost.

To define this type, specify the following keys in a schema:

• type_name: value of dict.
• key: description of key type.
• value: value type description.

Schema example:

type_v3={
  type_name=dict;
  key=int64;
  value={
    type_name=optional;
    item=string;
  };
}

Tagged

The tagged type helps annotate other types with a string. Any value of type T can serve as a value for type tagged<TAG_NAME,T>,
however, the types themselves will be considered different wherever YTsaurus compares schemas. For instance, when the possibility of merging two tables into one is being checked.

To define this type, specify the following keys in a schema:

• type_name: value of tagged.
• tag: tag name, must be a non-empty utf8 string.
• item: element type description.
  —
  Schema example:

type_v3={
  type_name=tagged;
  tag="image/svg";
  item="string";
}

Representing compound types in formats

Formats are used to read and write tables.
Some formats do not support composite data, and some, such as dsv / schemaful_dsv, will return an error in response to an attempt to read a composite value. For instance, Values of type "any" are not supported by the chosen format.

YSON

There are two YSON representations of composite types. The representation of types struct and variant are different:
the default representation is more convenient to use,
while the alternative representation yields better storage and processing performance.

You can switch between the representations by using the complex_type_mode flag. Legal values: named / positional.
Type representation descriptions are provided below. Unless otherwise specified, a type representation does not depend on the complex_type_mode setting.

Primitive types

Primitive types have a linear representation as a single YSON value.
The table shows a mapping between the primitive and the YSON types.

Decimal

Type decimal(p, s) is encoded as a YSON string with a binary representation of the decimal number.

Optional

The representation of type optional depends on its inner type.
This is required for backward compatibility with the columns with required=%false.
If T is an arbitrary type that is not optional, optional<T> is represented as follows:

• The Null value that is optional is represented by #.
• Otherwise, the T type value uses the conventional representation.

If T is an arbitrary type that is optional, optional<T> is represented as follows:

• The Null value of the outer optional is represented as #.
• Otherwise, the [ v ] representation is used (yson list of length 1), where v is the YSON representation of type T.

Example values, type optional<int64>:

#

-42

Example values, type optional<optional<int64>>:

#

[ # ]

[ -42 ]

List

Type list<T> is encoded as a YSON list whose elements are encoded representations of elements of type T.

Example value, type list<int64>:

[]

[42; -1;]

Struct

A struct representation depends on the values of the complex_type_mode flag.

Named representation (default)

The representation being described applies to the situation
when the YSON option of format complex_type_mode is not set or is set to complex_type_mode=named.

The struct is represented by a YSON dictionary where field names serve as keys and the contents of these fields are the values.

Example values, type struct<Foo:int64;Bar:optional<utf8>>:

{Foo=42;Bar=#;}

{Foo=-5;Bar="minus five";}

Positional representation

Where the complex_type_mode=positional option is set for the YSON format, a different representation is used.

A struct is encoded as a YSON list with the i-th position containing a YSON representation of the struct's i-th field.
The list may contain fewer elements than the number of fields in your struct, which means that the remaining types must be optional<T>,
and the fields are considered to have an empty optional value.

Example values, type struct<Foo:int64;Bar:optional<utf8>>:

[42; #;]
[42]

[-5;"minus five";]

Tuple

Type tuple is encoded as a fixed-length YSON list. The i-th position contains the i-th field's encoded value.

Example values, type tuple<int64;optional<utf8>>:

[42; #;]

[-5;"minus five";]

Variant

Unnamed variant

The unnamed option is represented by a YSON list of length 2 that includes the following elements:

• Alternative number (indexed at 0).
• An encoded value of the relevant alternative.

Example values, type variant<int64;optional<utf8>>:

[0; 42]

[1; #]

[1; "foo bar";]

Named variant option

Named representation (default)

The representation being described applies to the situation
when the YSON option of format complex_type_mode is not set or is set to complex_type_mode=named.

The named option is represented by a YSON list of length 2 that includes the following elements:

• Alternative name.
• An encoded value for the relevant alternative.

Example values, type `variant<Foo:int64;Bar:optional>:

[Foo; 42]

[Bar; #]

[Bar; "foo bar";]

Positional representation

If the complex_type_mode=positional option is set for a format.

The named option is represented by a YSON list of length 2 that includes the following elements:

• Index of alternative.
• An encoded value for the relevant alternative.

Example values, type variant<Foo:int64;Bar:optional<utf8>>:

[Foo; 42]

[Bar; #]

[Bar; "foo bar";]

Dict

Type dict is represented as a YSON list with each element being a YSON list of 2 elements: a key and a value.

Example values of type dict<int32;string>:

[[1;"one"];[4;"four"]]

[]

A dict may be represented as a YSON dictionary; however, a YSON dictionary only supports strings as keys whereas dict also supports other keys.

Tagged

Type tagged does not change its elements' YSON representations.