Basic built-in functions

Below are the general-purpose functions. For specialized functions, there are separate articles: aggregate, window, as well as for lists, dictionaries, structures, data types, and code generation.

COALESCE

Goes through the arguments from left to right and returns the first non-empty argument found. For the result to be guaranteed non-empty (not optional type), the rightmost argument must be of this type (a literal is often used). If there is one argument, returns it without change.

Signature

COALESCE(T?, ..., T)->T
COALESCE(T?, ..., T?)->T?

Enables you to pass potentially empty values to functions that cannot process them.

You can use the ?? operator as a shorter alternative. The NVL alias is also supported.

Examples

SELECT COALESCE(
  maybe_empty_column,
  "it's empty!"
) FROM my_table;

SELECT
  maybe_empty_column ?? "it's empty!"
FROM my_table;

SELECT NVL(
  maybe_empty_column,
  "it's empty!"
) FROM my_table;

All three examples above are equivalent.

LENGTH

Returns the length of the string in bytes. This function is also available under the LEN name .

Signature

LENGTH(T)->Uint32
LENGTH(T?)->Uint32?

Examples

SELECT LENGTH("foo");

SELECT LEN("bar");

SUBSTRING

Returns a substring.

Signature

Substring(String[, Uint32? [, Uint32?]])->String
Substring(String?[, Uint32? [, Uint32?]])->String?

Mandatory arguments:

• Source string;
• Position: The offset from the beginning of the string in bytes (integer) or NULL meaning "from the beginning".

Optional arguments:

• Substring length: The number of bytes starting from the specified position (an integer, or the default NULL meaning "up to the end of the source string").

Indexing starts from zero. If the specified position and length are beyond the string, returns an empty string.
If the input string is optional, the result is also optional.

Examples

SELECT SUBSTRING("abcdefg", 3, 1); -- d

SELECT SUBSTRING("abcdefg", 3); -- defg

SELECT SUBSTRING("abcdefg", NULL, 3); -- abc

FIND

Finding the position of a substring in a string.

Signature

Find(String, String[, Uint32?])->Uint32?
Find(String?, String[, Uint32?])->Uint32?
Find(Utf8, Utf8[, Uint32?])->Uint32?
Find(Utf8?, Utf8[, Uint32?])->Uint32?

Mandatory arguments:

• Source string;
• The substring being searched for.

Optional arguments:

• A position in bytes to start the search with (an integer or NULL by default that means "from the beginning of the source string").

Returns the first substring position found or NULL (meaning that the desired substring hasn't been found starting from the specified position).

Examples

SELECT FIND("abcdefg_abcdefg", "abc"); -- 0

SELECT FIND("abcdefg_abcdefg", "abc", 1); -- 8

SELECT FIND("abcdefg_abcdefg", "abc", 9); -- null

RFIND

Reverse finding the position of a substring in a string, from the end to the beginning.

Signature

RFind(String, String[, Uint32?])->Uint32?
RFind(String?, String[, Uint32?])->Uint32?
RFind(Utf8, Utf8[, Uint32?])->Uint32?
RFind(Utf8?, Utf8[, Uint32?])->Uint32?

Mandatory arguments:

• Source string;
• The substring being searched for.

Optional arguments:

• A position in bytes to start the search with (an integer or NULL by default, meaning "from the end of the source string").

Returns the first substring position found or NULL (meaning that the desired substring hasn't been found starting from the specified position).

Examples

SELECT RFIND("abcdefg_abcdefg", "bcd"); -- 9

SELECT RFIND("abcdefg_abcdefg", "bcd", 8); -- 1

SELECT RFIND("abcdefg_abcdefg", "bcd", 0); -- null

StartsWith, EndsWith

Checking for a prefix or suffix in a string.

Signatures

StartsWith(T str, U prefix)->Bool[?]

EndsWith(T str, U suffix)->Bool[?]

Mandatory arguments:

• Source string;
• The substring being searched for.

Arguments must be of the String/Utf8 (or optional String/Utf8) or string PostgreSQL (PgText/PgBytea/PgVarchar) type.
The function outputs an optional Bool (except when both arguments are non-optional — in this case, it returns a Bool).

Examples

SELECT StartsWith("abc_efg", "abc") AND EndsWith("abc_efg", "efg"); -- true

SELECT StartsWith("abc_efg", "efg") OR EndsWith("abc_efg", "abc"); -- false

SELECT StartsWith("abcd", NULL); -- null

SELECT EndsWith(NULL, Utf8("")); -- null

SELECT StartsWith("abc_efg"u, "abc"p) AND EndsWith("abc_efg", "efg"pv); -- true

IF

Checks the condition: IF(condition_expression, then_expression, else_expression).

It's a simplified alternative for CASE WHEN ... THEN ... ELSE ... END.

Signature

IF(Bool, T, T)->T
IF(Bool, T)->T?

You may omit the else_expression argument. In this case, if the condition is false (condition_expression returned false), an empty value is returned with the type corresponding to then_expression and allowing for NULL. Hence, the result will have an optional data type.

Examples

SELECT
  IF(foo > 0, bar, baz) AS bar_or_baz,
  IF(foo > 0, foo) AS only_positive_foo
FROM my_table;

NANVL

Replaces the values NaN (not a number) in the expressions that have the type Float, Double, or Optional.

Signature

NANVL(Float, Float)->Float
NANVL(Double, Double)->Double

Arguments:

1. The expression where you want to make a replacement.
2. The value to replace NaN.

If one of the arguments is Double, the result isDouble, otherwise, it's Float. If one of the arguments is Optional, then the result is Optional.

Examples

SELECT
  NANVL(double_column, 0.0)
FROM my_table;

Random...

Generates a pseudorandom number:

• Random(): A floating point number (Double) from 0 to 1.
• RandomNumber(): An integer from the complete Uint64 range.
• RandomUuid() — Uuid version 4.

Signatures

Random(T1[, T2, ...])->Double
RandomNumber(T1[, T2, ...])->Uint64
RandomUuid(T1[, T2, ...])->Uuid

No arguments are used for random number generation: they are only needed to control the time of the call. A new random number is returned at each call. Therefore:

• If Random is called again within a same query and with a same set of arguments, the same set of random numbers is returned. Keep in mind that we mean the arguments themselves (i.e., the text between parentheses) rather than their values.

• Calling of Random with the same set of arguments in different queries returns different sets of random numbers.

Use cases:

• SELECT RANDOM(1);: Get one random value for the entire query and use it multiple times (to get multiple random values, you can pass various constants of any type).
• SELECT RANDOM(1) FROM table;: The same random number for each row in the table.
• SELECT RANDOM(1), RANDOM(2) FROM table;: Two random numbers for each row of the table, all the numbers in each of the columns are the same.
• SELECT RANDOM(some_column) FROM table;: Different random numbers for each row in the table.
• SELECT RANDOM(some_column), RANDOM(some_column) FROM table;: Different random numbers for each row of the table, but two identical numbers within the same row.
• SELECT RANDOM(some_column), RANDOM(some_column + 1) FROM table; or SELECT RANDOM(some_column), RANDOM(other_column) FROM table;: Two columns, with different numbers in both.

Examples

SELECT
    Random(key) -- [0, 1)
FROM my_table;

SELECT
    RandomNumber(key) -- [0, Max<Uint64>)
FROM my_table;

SELECT
    RandomUuid(key) -- Uuid version 4
FROM my_table;

SELECT
    RANDOM(column) AS rand1,
    RANDOM(column) AS rand2, -- same as rand1
    RANDOM(column, 1) AS randAnd1, -- different from rand1/2
    RANDOM(column, 2) AS randAnd2 -- different from randAnd1
FROM my_table;

Udf

Builds a Callable object by the specified function name and optional external user types, RunConfig, and TypeConfig.

• Udf(Foo::Bar): The Foo::Bar function without any extra parameters.
• Udf(Foo::Bar)(1, 2, 'abc') — Calling the UDF Foo::Bar.
• Udf(Foo::Bar, Int32, @@{"device":"AHCI"}@@ as TypeConfig")(1, 2, 'abc'): Calling the Foo::Bar user-defined function with an additional Int32 type and a specified TypeConfig.
• Udf(Foo::Bar, "1e9+7" as RunConfig")(1, 'extended' As Precision): Calling the Foo::Bar user-defined function with the specified RunConfig and named parameters.

Signatures

Udf(Callable[, T1, T2, ..., T_N][, V1 as TypeConfig][,V2 as RunConfig]])->Callable

Where T1, T2, etc. are the custom external types.

Examples

$IsoParser = Udf(DateTime2::ParseIso8601);
SELECT $IsoParser("2022-01-01");

SELECT Udf(Unicode::IsUtf)("2022-01-01")

$config = @@{
    "name":"MessageFoo",
    "meta": "..."
}@@;
SELECT Udf(Protobuf::TryParse, $config As TypeConfig)("")

CurrentUtc...

CurrentUtcDate(), CurrentUtcDatetime() and CurrentUtcTimestamp(): Getting the current date and/or time in UTC. The result data type is specified at the end of the function name.

Signatures

CurrentUtcDate(...)->Date
CurrentUtcDatetime(...)->Datetime
CurrentUtcTimestamp(...)->Timestamp

The arguments are optional and work the same as RANDOM.

Examples

SELECT CurrentUtcDate();

SELECT CurrentUtcTimestamp(TableRow()) FROM my_table;

CurrentTz...

CurrentTzDate(), CurrentTzDatetime(), and CurrentTzTimestamp(): Get the current date and/or time in the IANA time zone specified in the first argument. The result data type is specified at the end of the function name.

Signatures

CurrentTzDate(String, ...)->TzDate
CurrentTzDatetime(String, ...)->TzDatetime
CurrentTzTimestamp(String, ...)->TzTimestamp

The arguments that follow are optional and work the same as RANDOM.

Examples

SELECT CurrentTzDate("Europe/Moscow");

SELECT CurrentTzTimestamp("Europe/Moscow", TableRow()) FROM my_table;

AddTimezone

Adding the time zone information to the date/time in UTC. In the result of SELECT or after CAST, a String will be subject to the time zone rules used to calculate the time offset.

Signature

AddTimezone(Date, String)->TzDate
AddTimezone(Date?, String)->TzDate?
AddTimezone(Datetime, String)->TzDatetime
AddTimezone(Datetime?, String)->TzDatetime?
AddTimezone(Timestamp, String)->TzTimestamp
AddTimezone(Timestamp?, String)->TzTimestamp?

Arguments:

1. Date: the type is Date/Datetime/Timestamp.
2. IANA name of the time zone.

Result type: TzDate/TzDatetime/TzTimestamp, depending on the input data type.

Examples

SELECT AddTimezone(Datetime("2018-02-01T12:00:00Z"), "Europe/Moscow");

RemoveTimezone

Removing the time zone data and converting the value to date/time in UTC.

Signature

RemoveTimezone(TzDate)->Date
RemoveTimezone(TzDate?)->Date?
RemoveTimezone(TzDatetime)->Datetime
RemoveTimezone(TzDatetime?)->Datetime?
RemoveTimezone(TzTimestamp)->Timestamp
RemoveTimezone(TzTimestamp?)->Timestamp?

Arguments:

1. Date: the type is TzDate/TzDatetime/TzTimestamp.

Result type: Date/Datetime/Timestamp, depending on the input data type.

Examples

SELECT RemoveTimezone(TzDatetime("2018-02-01T12:00:00,Europe/Moscow"));

Version

Version() returns a string describing the current version of the node processing the query. In some cases, such as during rolling cluster upgrades, it might return different strings depending on which node is processing the query. The function doesn't accept any arguments.

Examples

SELECT Version();

CurrentLanguageVersion

CurrentLanguageVersion() returns a string describing the current version (if defined) of the language selected for the current query or an empty string.

Examples

SELECT CurrentLanguageVersion();

MAX_OF, MIN_OF, GREATEST, and LEAST

Returns the minimum or maximum among N arguments. Those functions let you replace the SQL standard statement CASE WHEN a < b THEN a ELSE b END that would be too verbose for N more than two.

Signatures

MIN_OF(T[,T,...})->T
MAX_OF(T[,T,...})->T

The argument types must be mutually castable and accept NULL.

GREATEST is a synonym for MAX_OF and LEAST is a synonym for MIN_OF.

Examples

SELECT MIN_OF(1, 2, 3);

AsTuple, AsStruct, AsList, AsDict, AsSet, AsListStrict, AsDictStrict and AsSetStrict

Creates containers of the appropriate types. Operator writing of container literals is also available.

Features:

• Container items are passed through arguments, so the number of items in the resulting container is equal to the number of passed arguments, except when the dict keys are repeated.
• In AsTuple and AsStruct, can be invoked without arguments and arguments can have different types.
• Field names in AsStruct are set via AsStruct(field_value AS field_name).
• You need at least one argument to create a list if you need to output item types. To create an empty list with the specified item type, use the ListCreate function. You can create an empty list as an AsList() invocation without arguments. In this case, this expression will have the EmptyList type.
• You need at least one argument to create a dict if you need to output item types. To create an empty dict with the specified item type, use the DictCreate function. You can create an empty dict as an AsDict() invocation without arguments. In this case, this expression will have the EmptyDict type.
• You need at least one argument to create a set if you need to output item types. To create an empty set with the specified item type, use the SetCreate function. You can create an empty set as an AsSet() invocation without arguments. In this case, this expression will have the EmptyDict type.
• AsList outputs the general type of list items. A type error is generated if there are incompatible types.
• AsDict outputs the general types of keys and values separately. A type error is generated if there are incompatible types.
• AsSet outputs the general types of keys. A type error is generated if there are incompatible types.
• AsListStrict, AsDictStrict, and AsSetStrict require the same type for arguments.
• In AsDict and AsDictStrict, Tuple of two items (key and value) is expected as arguments. If keys are repeated, only the value for the first key remains in the dict.
• In AsSet and AsSetStrict, keys are expected as arguments.

Examples

SELECT
  AsTuple(1, 2, "3") AS `tuple`,
  AsStruct(
    1 AS a,
    2 AS b,
    "3" AS c
  ) AS `struct`,
  AsList(1, 2, 3) AS `list`,
  AsDict(
    AsTuple("a", 1),
    AsTuple("b", 2),
    AsTuple("c", 3)
  ) AS `dict`,
  AsSet(1, 2, 3) AS `set`

Container literals

For some containers, an operator format of their literal values is possible:

• Tuple: (value1, value2...).
• Structure: <|name1: value1, name2: value2...|>.
• List: [value1, value2,...].
• Dict: {key1: value1, key2: value2...}.
• Set: {key1, key2...}.

An insignificant trailing comma is allowed in all cases. This comma is mandatory for a tuple with one item: (value1,).
For field names in the structure literal, you can use an expression that can be counted in evaluation time, for example, string literals, as well as identifiers (including in backticks).

For a list inside, the AsList function is used, for a dict — the AsDict function, for a set — the AsSet function, for a tuple — the AsTuple function, and for a structure — the AsStruct function.

Examples

$name = "computed " || "member name";
SELECT
  (1, 2, "3") AS `tuple`,
  <|
    `complex member name`: 2.3,
    b: 2,
    $name: "3",
    "inline " || "computed member name": false
  |> AS `struct`,
  [1, 2, 3] AS `list`,
  {
    "a": 1,
    "b": 2,
    "c": 3,
  } AS `dict`,
  {1, 2, 3} AS `set`

Variant

Variant() creates a variant value over a tuple or structure.

Signature

Variant(T, String, Type<Variant<...>>)->Variant<...>

Arguments:

• Value
• String with a field name or tuple index
• Variant type

Example

$var_type = Variant<foo: Int32, bar: Bool>;

SELECT
   Variant(6, "foo", $var_type) as Variant1Value,
   Variant(false, "bar", $var_type) as Variant2Value;

AsVariant

AsVariant() creates a value of a variant on a structure with one field. This value can be implicitly converted to any variant over a structure that has a matching data type for this field name and might include more fields with other names.

Signature

AsVariant(T, String)->Variant

Arguments:

• Value
• A string with the field name

Example

SELECT
   AsVariant(6, "foo") as VariantValue

Visit, VisitOrDefault

Processes possible values of a variant represented by a structure or tuple using provided handler functions for each field or item.

Signature

Visit(Variant<key1: K1, key2: K2, ...>, K1->R AS key1, K2->R AS key2, ...)->R
Visit(Variant<K1, K2, ...>, K1->R, K2->R, ...)->R

VisitOrDefault(Variant<K1, K2, ...>{Flags:AutoMap}, R, [K1->R, [K2->R, ...]])->R
VisitOrDefault(Variant<key1: K1, key2: K2, ...>{Flags:AutoMap}, R, [K1->R AS key1, [K2->R AS key2, ...]])->R

Arguments

• When the variant is represented by a structure: accepts the variant as the positional argument and one named argument (handler) for each field of the structure.
• When the variant is represented by a tuple: accepts the variant itself and one handler for each item in the tuple as positional arguments.
• The VisitOrDefault modification accepts an additional positional argument (the second one), which is the default value and which enables you to omit certain handlers.

Example

$vartype = Variant<num: Int32, flag: Bool, str: String>;
$handle_num = ($x) -> { return 2 * $x; };
$handle_flag = ($x) -> { return If($x, 200, 10); };
$handle_str = ($x) -> { return Unwrap(CAST(LENGTH($x) AS Int32)); };

$visitor = ($var) -> { return Visit($var, $handle_num AS num, $handle_flag AS flag, $handle_str AS str); };
SELECT
    $visitor(Variant(5, "num", $vartype)),                -- 10
    $visitor(Just(Variant(True, "flag", $vartype))),      -- Just(200)
    $visitor(Just(Variant("somestr", "str", $vartype))),  -- Just(7)
    $visitor(Nothing(OptionalType($vartype))),            -- Nothing(Optional<Int32>)
    $visitor(NULL)                                        -- NULL
;

VariantItem

Returns the value of a homogeneous variant (a variant containing fields or items of the same type).

Signature

VariantItem(Variant<key1: K, key2: K, ...>{Flags:AutoMap})->K
VariantItem(Variant<K, K, ...>{Flags:AutoMap})->K

Example

$vartype1 = Variant<num1: Int32, num2: Int32, num3: Int32>;
SELECT
    VariantItem(Variant(7, "num2", $vartype1)),          -- 7
    VariantItem(Just(Variant(5, "num1", $vartype1))),    -- Just(5)
    VariantItem(Nothing(OptionalType($vartype1))),       -- Nothing(Optional<Int32>)
    VariantItem(NULL)                                    -- NULL
;

Way

Returns an active field (active index) of a variant over structure (tuple).

Signature

Way(Variant<key1: K1, key2: K2, ...>{Flags:AutoMap})->Utf8
Way(Variant<K1, K2, ...>{Flags:AutoMap})->Uint32

Example

$vr = Variant(1, "0", Variant<Int32, String>);
$vrs = Variant(1, "a", Variant<a:Int32, b:String>);


SELECT Way($vr);  -- 0
SELECT Way($vrs); -- "a"

DynamicVariant

Creates an instance of a homogeneous variant (a variant containing fields or items of the same type), where the variant index or field can be set dynamically. If the index or field name does not exist, returns NULL.
The reverse function is VariantItem.

Signature

DynamicVariant(item:T,index:Uint32?,Variant<T, T, ...>)->Optional<Variant<T, T, ...>>
DynamicVariant(item:T,index:Utf8?,Variant<key1: T, key2: T, ...>)->Optional<Variant<key1: T, key2: T, ...>>

Example

$dt = Int32;
$tvt = Variant<$dt,$dt>;
SELECT ListMap([(10,0u),(20,2u),(30,NULL)],($x)->(DynamicVariant($x.0,$x.1,$tvt))); -- [0: 10,NULL,NULL]

$dt = Int32;
$svt = Variant<x:$dt,y:$dt>;
SELECT ListMap([(10,'x'u),(20,'z'u),(30,NULL)],($x)->(DynamicVariant($x.0,$x.1,$svt))); -- [x: 10,NULL,NULL]

Enum

Enum() creates an enumeration value.

Signature

Enum(String, Type<Enum<...>>)->Enum<...>

Arguments:

• A string with the field name
• Enumeration type

Example

$enum_type = Enum<Foo, Bar>;
SELECT
   Enum("Foo", $enum_type) as Enum1Value,
   Enum("Bar", $enum_type) as Enum2Value;

AsEnum

AsEnum() creates an enumeration value with one element. This value can be implicitly cast to any enumeration containing such a name.

Signature

AsEnum(String)->Enum<'tag'>

Arguments:

• A string with the name of an enumeration item

Example

SELECT
   AsEnum("Foo");

AsTagged, Untag

Wraps a value in Tagged data type with the specified tag preserving the physical data type. Untag: Reverse operation.

Signature

AsTagged(T, tagName:String)->Tagged<T,tagName>
AsTagged(T?, tagName:String)->Tagged<T,tagName>?

Untag(Tagged<T, tagName>)->T
Untag(Tagged<T, tagName>?)->T?

Mandatory arguments:

1. Value of an arbitrary type.
2. Tag name.

Returns a copy of the value from the first argument with the specified tag in the data type.

Examples of use cases:

• Returning to the client to display media files of base64-encoded strings in the web interface.
• Protecting at the boundaries of the UDF call against the transfer of incorrect values.
• Additional clarifications at the returned column type level.

TablePath

Access to the current table name, which might be needed when using CONCAT, RANGE, and other related mechanisms.

Signature

TablePath()->String

No arguments. Returns a string with the full path or an empty string and warning when used in an unsupported context (for example, when working with a subquery or a range of 1000+ tables).

Examples

SELECT TablePath() FROM CONCAT(table_a, table_b);

SELECT key, tpath_ AS path FROM (SELECT a.*, TablePath() AS tpath_ FROM RANGE(`my_folder`) AS a)
WHERE key IN $subquery;

TableName

Get the table name based on the table path. You can obtain the path using the TablePath function or as the Path column when using the table function FOLDER.

Signature

TableName()->String
TableName(String)->String
TableName(String, String)->String

Optional arguments:

• Path to the table, TablePath() is used by default (see also its limitations).
• Specifying the system ("yt") whose rules are used to determine the table name. You need to specify the system only if USE doesn't specify the current cluster.

Examples

USE hahn;
SELECT TableName() FROM CONCAT(table_a, table_b);

SELECT TableName(Path, "yt") FROM cluster.FOLDER(folder_name);

TableRecordIndex

Access to the current sequence number of a row in the physical source table, starting from 1 (depends on the storage implementation).

Signature

TableRecordIndex()->Uint64

No arguments. When used together with CONCAT, RANGE, and other related mechanisms, numbering is reset for each input table. If used in an incorrect context, it returns 0.

Example

SELECT TableRecordIndex() FROM my_table;

TableRow, JoinTableRow

Getting the entire table row as a structure. No arguments. JoinTableRow in case of JOIN always returns a structure with table prefixes.

Signature

TableRow()->Struct

Example

SELECT TableRow() FROM my_table;

FileContent and FilePath

You can attach arbitrary named files to your query both in the console and web interfaces. With these functions, you can use the name of the attached file to get its contents or the path in the sandbox, and then use it as you like in the query.

Signatures

FilePath(String)->String
FileContent(String)->String

The FileContent and FilePath argument is a string with an alias.

Examples

SELECT "Content of "
  || FilePath("my_file.txt")
  || ":\n"
  || FileContent("my_file.txt");

FolderPath

Getting the path to the root of a directory with several "attached" files with the common prefix specified.

Signature

FolderPath(String)->String

The argument is a string with a prefix among aliases.

See also PRAGMA File and PRAGMA Folder.

Examples

PRAGMA File("foo/1.txt", "http://url/to/somewhere");
PRAGMA File("foo/2.txt", "http://url/to/somewhere/else");
PRAGMA File("bar/3.txt", "http://url/to/some/other/place");

SELECT FolderPath("foo"); -- The directory at the return path will
                          -- include the files 1.txt and 2.txt downloaded by the above links

ParseFile

Get a list of values from the attached text file. You can use it in combination with IN and attaching the file via URL (instructions on how to attach files in the web interface and in the client).

Only one file format is supported: one value per line. For something more sophisticated, you'd currently need to write a small UDF in Python.

Signature

ParseFile(String, String)->List<T>

Two required arguments:

1. List cell type: only strings and numeric types are supported.
2. The name of the attached file.

Examples

SELECT ListLength(ParseFile("String", "my_file.txt"));

SELECT * FROM my_table
WHERE int_column IN ParseFile("Int64", "my_file.txt");

WeakField

Fetches a table column from a strong schema, if it is in a strong schema, or from the _other and _rest fields. If the value is missing, it returns NULL.

Syntax: WeakField([<table>.]<field>, <type>[, <default_value>]).

The default value is used only if the column is missing in the data schema. To use the default value in any case, use COALESCE.

Examples

SELECT
    WeakField(my_column, String, "no value"),
    WeakField(my_table.other_column, Int64)
FROM my_table;

Ensure...

Checking for the user conditions:

• Ensure(): Checking whether the predicate is true at query execution.
• EnsureType(): Checking that the expression type exactly matches the specified type.
• EnsureConvertibleTo(): A soft check of the expression type (with the same rules as for implicit type conversion).

If the check fails, the entire query fails.

Signatures

Ensure(T, Bool, String)->T
EnsureType(T, Type<T>, String)->T
EnsureConvertibleTo(T, Type<T>, String)->T

Arguments:

1. An expression that will result from a function call if the check is successful. It's also checked for the data type in the corresponding functions.
2. Ensure uses a Boolean predicate that is checked for being true. The other functions use the data type that can be obtained using the relevant functions or a string literal with the text description of the type.
3. An optional string with an error comment to be included in the overall error message when the query is complete. The data itself can't be used for type checks, since the data check is performed at query validation (or can be an arbitrary expression in the case of Ensure).

To check the conditions based on the final calculation result, it's convenient to combine Ensure with DISCARD SELECT.

Examples

SELECT Ensure(
    value,
    value < 100,
    "value out or range"
) AS value FROM my_table;

SELECT EnsureType(
    value,
    TypeOf(other_value),
    "expected value and other_value to be of same type"
) AS value FROM my_table;

SELECT EnsureConvertibleTo(
    value,
    Double?,
    "expected value to be numeric"
) AS value FROM my_table;

AssumeStrict

Signature

AssumeStrict(T)->T

The AssumeStrict function returns its argument. Using this function is a way to tell the YQL optimizer that the expression in the argument is strict, i.e. free of runtime errors.
Most of the built-in YQL functions and operators are strict, but there are exceptions like Unwrap and Ensure.
Besides that, a non-strict expression is considered a UDF call.

If you are sure that no runtime errors actually occur when computing the expression, we recommend using AssumeStrict.

Example

SELECT * FROM T1 AS a JOIN T2 AS b USING(key)
WHERE AssumeStrict(Unwrap(CAST(a.key AS Int32))) == 1;

In this example, we assume that all values of the a.key text column in table T1 are valid numbers, so Unwrap does not cause an error.
If there is AssumeStrict, the optimizer will be able to perform filtering first and then JOIN.
Without AssumeStrict, such optimization is not performed: the optimizer must take into account the situation when there are non-numeric values in the a.key column which are filtered out by JOIN.

Likely

Signature

Likely(Bool)->Bool
Likely(Bool?)->Bool?

The Likely function returns its argument. This function is a hint for the optimizer that tells it that in most cases its argument will be True.
For example, if such a function is used in WHERE, it means that the filter is weekly selective.

Example

SELECT * FROM T1 AS a JOIN T2 AS b USING(key)
WHERE Likely(a.amount > 0)  -- This condition is almost always true

When you use Likely, the optimizer won't attempt to perform filtering before JOIN.

EvaluateExpr, EvaluateAtom

Evaluate an expression before the start of the main calculation and input its result to the query as a literal (constant). In many contexts where the standard SQL would only expect a constant (for example in table names, number of rows in LIMIT, and so on), this functionality is automatically activated implicitly.

EvaluateExpr can be used where the grammar already expects an expression. For example, you can use it to:

• Round the current time to days, weeks, or months and add the time to the query. This will ensure valid query caching, although normally, when you use current-time functions, caching is disabled completely.
• Run a heavy calculation with a small result once per query instead of once per job.

You can use EvaluateAtom to create an atom dynamically. However, since atoms are mainly controlled from a lower s-expressions level, it is generally not recommended to use this function directly.

The only argument for both functions is the expression for calculation and substitution.

Restrictions:

• The expression must not trigger MapReduce operations.

Examples

$now = CurrentUtcDate();
SELECT EvaluateExpr(
    DateTime::MakeDate(DateTime::StartOfWeek($now)
    )
);

Literals of primitive types

For primitive types, you can create literals based on string literals.

Syntax

<Primitive type>( <string>[, <additional attributes>] )

Unlike CAST("myString" AS MyType):

• The check for literal's castability to the desired type occurs at validation.
• The result is non-optional.

For the Date, Datetime, Timestamp, and Interval data types, literals are supported only in the format conforming to ISO 8601. Interval has the following differences from the standard:

• It supports the negative sign for shifts to the past.
• Microseconds can be expressed as fractional parts of seconds.
• You can't use units of measurement exceeding one week.
• The options with the beginning/end of the interval and with repetitions, are not supported.

For the TzDate, TzDatetime, TzTimestamp data types, literals are also set in the format conforming to ISO 8601, but instead of the optional Z suffix, they specify the IANA name of the time zone, separated by a comma (for example, GMT or Europe/Moscow).

For the Decimal parameter data type, two additional arguments are specified:

• The total number of decimal digits (up to 35, inclusive).
• The number of decimal digits after the decimal point (out of the total number, i.e. strictly no more than the previous argument).

Examples

SELECT
  Bool("true"),
  Uint8("0"),
  Int32("-1"),
  Uint32("2"),
  Int64("-3"),
  Uint64("4"),
  Float("-5"),
  Double("6"),
  Decimal("1.23", 5, 2), -- up to 5 decimal points, 2 of which follow a comma
  String("foo"),
  Utf8("hello"),
  Yson("<a=1>[3;%false]"),
  Json(@@{"a":1,"b":null}@@),
  Date("2017-11-27"),
  Datetime("2017-11-27T13:24:00Z"),
  Timestamp("2017-11-27T13:24:00.123456Z"),
  Interval("P1DT2H3M4.567890S"),
  TzDate("2017-11-27,Europe/Moscow"),
  TzDatetime("2017-11-27T13:24:00,America/Los_Angeles"),
  TzTimestamp("2017-11-27T13:24:00.123456,GMT"),
  Uuid("f9d5cc3f-f1dc-4d9c-b97e-766e57ca4ccb");

Access to the metadata of the current operation

When you run YQL operations via the web interface or HTTP API, you get access to the following data:

• CurrentOperationId(): The private ID of the operation.
• CurrentOperationSharedId(): The public ID of the operation.
• CurrentAuthenticatedUser(): The username of the current user.

Signatures

CurrentOperationId()->String
CurrentOperationSharedId()->String
CurrentAuthenticatedUser()->String

No arguments.

If this data is missing, for example, when you run operations in the embedded mode, the functions return an empty string.

Examples

SELECT
    CurrentOperationId(),
    CurrentOperationSharedId(),
    CurrentAuthenticatedUser();

ToBytes and FromBytes

Conversion of primitive data types to a string with their binary representation and back. Numbers are represented in the little endian encoding.

Signatures

ToBytes(T)->String
ToBytes(T?)->String?

FromBytes(String, Type<T>)->T?
FromBytes(String?, Type<T>)->T?

Examples

SELECT
    ToBytes(123), -- "\u0001\u0000\u0000\u0000"
    FromBytes(
        "\xd2\x02\x96\x49\x00\x00\x00\x00",
        Uint64
    ); -- 1234567890ul

ByteAt

Getting the byte value in the string by the index from its beginning. If the index is invalid, NULL is returned.

Signature

ByteAt(String, Uint32)->Uint8
ByteAt(String?, Uint32)->Uint8?

ByteAt(Utf8, Uint32)->Uint8
ByteAt(Utf8?, Uint32)->Uint8?

Arguments:

1. String: String or Utf8.
2. Index: Uint32.

Examples

SELECT
    ByteAt("foo", 0), -- 102
    ByteAt("foo", 1), -- 111
    ByteAt("foo", 9); -- NULL

...Bit

TestBit(), ClearBit(), SetBit(), and FlipBit(): Test, clear, set, or flip a bit in an unsigned number by the specified bit sequence number.

Signatures

TestBit(T, Uint8)->Bool
TestBit(T?, Uint8)->Bool?
TestBit(String, Uint8)->Bool?
TestBit(String?, Uint8)->Bool?

ClearBit(T, Uint8)->T
ClearBit(T?, Uint8)->T?

SetBit(T, Uint8)->T
SetBit(T?, Uint8)->T?

FlipBit(T, Uint8)->T
FlipBit(T?, Uint8)->T?

Arguments:

1. An unsigned number to perform the desired operation on. TestBit is also implemented for strings (see the description below).
2. Bit number.

TestBit returns true/false. Other functions return a copy of their first argument with the corresponding transformation performed.

TestBit for string arguments works as follows:

1. Based on the second argument, the function selects the corresponding byte from the beginning of the string.
2. In that byte, it then selects the corresponding low-order bit.

Examples

SELECT
    TestBit(1u, 0), -- true
    TestBit('ax', 12) -- true (second byte, fourth bit)
    SetBit(8u, 0); -- 9

Abs

Absolute value of the number.

Signature

Abs(T)->T
Abs(T?)->T?

Examples

SELECT Abs(-123); -- 123

Just

Just(): Change the data type of the value to an optional type derived from the current data type (for example, T becomes T?).

Signature

Just(T)->T?

Examples

SELECT
  Just("my_string"); --  String?

Unwrap

Unwrap(): Converting the optional value of the data type to the corresponding non-optional type, raising a runtime error if the data is NULL. This means that T? becomes T.

If the value is not optional, the function returns its first argument without change.

Signature

Unwrap(T?)->T
Unwrap(T?, Utf8)->T
Unwrap(T?, String)->T

Arguments:

1. Value to be converted.
2. An optional string with a comment for the error text.

The reverse operation is Just.

Examples

$value = Just("value");

SELECT Unwrap($value, "Unexpected NULL for $value");

Nothing

Nothing(): Create an empty value for the specified Optional data type.

Signature

Nothing(Type<T?>)->T?

Examples

SELECT
  Nothing(String?); -- A NULL value with the String? type

Learn more about ParseType and other functions for data types.

Callable

Create a callable value with the given signature from a lambda function. Usually used to place callable values in containers.

Signature

Callable(Type<Callable<(...)->T>>, lambda)->Callable<(...)->T>

Arguments:

1. Type.
2. Lambda function.

Examples

$lambda = ($x) -> {
    RETURN CAST($x as String)
};

$callables = AsTuple(
    Callable(Callable<(Int32)->String>, $lambda),
    Callable(Callable<(Bool)->String>, $lambda),
);

SELECT $callables.0(10), $callables.1(true);

Pickle, Unpickle

Pickle() and StablePickle() serialize an arbitrary object into a sequence of bytes, if possible. Typical non-serializable objects are Callable and Resource. The serialization format is not versioned and can be used within a single query. For the Dict type, the StablePickle function pre-sorts the keys, and for Pickle, the order of dictionary elements in the serialized representation isn't defined.

Unpickle() is the inverse operation (deserialization), where with the first argument being the data type of the result and the second argument is the string with the result of Pickle() or StablePickle().

Signatures

Pickle(T)->String
StablePickle(T)->String
Unpickle(Type<T>, String)->T

Examples

SELECT *
FROM my_table
WHERE Digest::MurMurHash32(
        Pickle(TableRow())
    ) % 10 == 0; -- from practical viewpoint, it's better to use TABLESAMPLE

$buf = Pickle(123);
SELECT Unpickle(Int32, $buf);

StaticMap

Transforms a structure or tuple by applying a lambda function to each item.

Signature

StaticMap(Struct<...>, lambda)->Struct<...>
StaticMap(Tuple<...>, lambda)->Tuple<...>

Arguments:

• Structure or tuple.
• Lambda for processing items.

Result: a structure or tuple with the same number and naming of items as in the first argument, and with item data types determined by lambda results.

Examples

SELECT *
FROM (
    SELECT
        StaticMap(TableRow(), ($item) -> {
            return CAST($item AS String);
        })
    FROM my_table
) FLATTEN COLUMNS; -- converting all columns to rows

StaticZip

Merges structures or tuples element-by-element. All arguments (one or more) must be either structures with the same set of fields or tuples of the same length.
The result will be a structure or tuple, respectively.
Each item of the result is a tuple comprised of items taken from arguments.

Signature

StaticZip(Struct, Struct)->Struct
StaticZip(Tuple, Tuple)->Tuple

Examples

$one = <|k1:1, k2:2.0|>;
$two = <|k1:3.0, k2:4|>;

-- element-wise addition of two structures
SELECT StaticMap(StaticZip($one, $two), ($tuple)->($tuple.0 + $tuple.1)) AS sum;

StaticFold, StaticFold1

StaticFold(obj:Struct/Tuple, initVal, updateLambda)
StaticFold1(obj:Struct/Tuple, initLambda, updateLambda)

Static left-associative fold over a structure or tuple.
Tuples are folded from the lower index to the higher one; for structures, the order is not guaranteed.

• obj: Object whose elements are to be folded.
• initVal: (for StaticFold) Initial fold state.
• initLambda: (for StaticFold1) Function that produces an initial fold state based on the first element.
• updateLambda: Function that updates a state (accepts the next object element and the previous state in the arguments).

StaticFold(<|key_1:$el_1, key_2:$el_2, ..., key_n:$el_n|>, $init, $f) transforms into fold:

$f($el_n, ...$f($el_2, $f($init, el_1))...)

StaticFold1(<|key_1:$el_1, key_2:$el_2, ..., key_n:$el_n|>, $f0, $f):

$f($el_n, ...$f($el_2, $f($f0($init), el_1))...)

StaticFold1(<||>, $f0, $f) returns NULL.

The same logic applies to tuples.

AggregationFactory

Create the aggregate function factory to separate the process of describing how to aggregate data and which data to apply it to.

Arguments:

1. A string in quotation marks that is the name of an aggregate function, for example, "MIN".
2. Optional aggregate function parameters that do not depend on the data. For example, the percentile value in PERCENTILE.

The resulting factory can be used as a second parameter of the AGGREGATE_BY function.
If the aggregate function works on two columns instead of one, for example, MIN_BY, Tuple of two values is passed as a first argument in AGGREGATE_BY. For more information, see the description of this aggregate function.

Examples

$factory = AggregationFactory("MIN");
SELECT
    AGGREGATE_BY(value, $factory) AS min_value -- apply MIN aggregation to value column
FROM my_table;

AggregateTransformInput

AggregateTransformInput() transforms the aggregate function factory, for example, the one obtained via the AggregationFactory function, into another factory in which the specified transformation of input items is performed before the aggregation starts.

Arguments:

1. Aggregate function factory.
2. Lambda function with one argument which transforms an input item.

Examples

$f = AggregationFactory("sum");
$g = AggregateTransformInput($f, ($x) -> (cast($x as Int32)));
$h = AggregateTransformInput($f, ($x) -> ($x * 2));
SELECT ListAggregate([1,2,3], $f); -- 6
SELECT ListAggregate(["1","2","3"], $g); -- 6
SELECT ListAggregate([1,2,3], $h); -- 12

AggregateTransformOutput

AggregateTransformOutput() transforms the aggregate function factory, for example, the one obtained via the AggregationFactory function, into another factory in which the specified transformation of the result is performed after the aggregation is completed.

Arguments:

1. Aggregate function factory.
2. Lambda function with one argument which transforms the result.

Examples

$f = AggregationFactory("sum");
$g = AggregateTransformOutput($f, ($x) -> ($x * 2));
SELECT ListAggregate([1,2,3], $f); -- 6
SELECT ListAggregate([1,2,3], $g); -- 12

AggregateFlatten

Adapts the aggregate function factory, for example, the one obtained via the AggregationFactory function, so that it performs aggregation on input items — lists. This operation is similar to FLATTEN LIST BY: each item in the list is aggregated.

Arguments:

1. Aggregate function factory.

Examples

$i = AggregationFactory("AGGREGATE_LIST_DISTINCT");
$j = AggregateFlatten($i);
SELECT AggregateBy(x, $j) from (
   SELECT [1,2] as x
   union all
   SELECT [2,3] as x
); -- [1, 2, 3]