Window Functions

    +
    Window functions are used to compute cumulative, moving, and reporting aggregations.

    Window functions are used to compute an aggregate or cumulative value, based on a group of objects. The objects are not grouped into a single output object — each object remains separate in the query output.

    All window functions must have a window definition. This divides the query result set into one or more partitions, and determines the order of objects in those partitions. Within each partition, a movable window frame is defined for every input object. The window frame determines the objects to be used by the window function.

    N1QL has a dedicated set of window functions. Each window function call includes an OVER clause, which introduces the window specification. Some window functions take additional window options, which are specified by further clauses before the OVER clause.

    In Couchbase Server Enterprise Edition, aggregate functions can also be used as window functions when they are used with an OVER clause.

    In Couchbase Server 7.0 and later, window functions (and aggregate functions used as window functions) may specify their own inline window definitions, or they may refer to a named window defined by the WINDOW clause elsewhere in the query. By defining a named window with the WINDOW clause, you can reuse the window definition across several functions in the query, potentially making the query easier to write and maintain.

    Syntax

    This section shows the generic syntax of window functions, including window options and the OVER clause. See the sections below for details of the syntax of individual window functions.

    Window Function

    window-function-name '(' window-function-arguments ')' window-function-options? over-clause

    Window Function Arguments

    window-function-arguments ::= [ expr [ ',' expr [ ',' expr ] ] ]
    ( expr ( ',' expr ( ',' expr )? )? )?

    See below for details of the arguments for individual functions.

    Window Function Options

    window-function-options ::= [ nthval-from ] [ nulls-treatment ]
    nth-val-from? nulls-treatment?

    Window function options can only be used with some window functions, as described below.

    From Modifier

    nthval-from ::= FROM ( FIRST | LAST )
    'FROM' ( 'FIRST' | 'LAST' )

    The from modifier determines whether the computation begins at the first or last object in the window.

    This clause can only be used with the NTH_VALUE() function.

    This clause is optional. If omitted, the default setting is FROM FIRST.

    Nulls Modifier

    nulls-treatment::= ( RESPECT | IGNORE ) NULLS
    ( 'RESPECT' | 'IGNORE' ) 'NULLS'

    The nulls modifier determines whether NULL values are included in the computation, or ignored. MISSING values are treated the same way as NULL values.

    This clause can only be used with the FIRST_VALUE(), LAST_VALUE(), NTH_VALUE(), LAG(), and LEAD() functions.

    This clause is optional. If omitted, the default setting is RESPECT NULLS.

    OVER Clause

    over-clause ::= OVER ( window-ref | '(' window-definition ')' )
    window-function-type '(' window-function-arguments ')' window-function-options? 'OVER' '(' window-definition ')'

    The OVER clause introduces the window specification for the function. There are two ways of specifying the window.

    • An inline window definition specifies the window directly within the function call. It is delimited by parentheses () and has exactly the same syntax as the window definition in a WINDOW clause. For further details, refer to Window Definition.

    • A window reference refers to a named window, which must be defined by a WINDOW clause in the same query block as the function call. For further details, refer to WINDOW Clause.

    With some window functions, the window specification may include a window partition clause, a window order clause, and a window frame clause. With other window functions, the window specification may only include a subset of these clauses. See the sections below for details of the clauses permitted within the window specification for each function.

    Note that any restrictions on the clauses permitted in the window specification apply equally, whether the function has an inline window definition, or a reference to a named window.

    Usage

    Window functions can only appear in the SELECT projection clause or query ORDER BY clause.

    Any expression within a window function may be a subquery. However, this will lead to repeated evaluation when the query is processed. If required, use a LET clause, a WITH clause, or an intervening subquery to avoid repeated evaluation.
    An expression within the window function may not contain another, nested window function. If necessary, you can specify one window function in a subquery, and another window function in the parent query.

    Window functions are processed after JOIN clauses, the LET clause, the WHERE clause, and the GROUP BY, LETTING, and HAVING clauses. Window functions therefore operate on the query result set.

    CUME_DIST()

    Description

    Returns the percentile rank of the current object as part of the cumulative distribution — that is, the number of objects ranked lower than or equal to the current object, including the current object, divided by the total number of objects in the window partition.

    Syntax

    cume-dist-function ::= CUME_DIST '()' OVER ( '(' window-definition ')' | window-ref )
    'CUME_DIST' '()' 'OVER' ( '(' window-definition ')' | window-ref )

    Arguments

    None.

    Window Specification

    The window specification may include an optional window partition clause, and must include a window order clause.

    Return Value

    A number greater than 0 and less than or equal to 1. The higher the value, the higher the ranking.

    Example

    For each destination airport, find the cumulative distribution of all routes in order of distance.

    SELECT d.id, d.destinationairport, CUME_DIST() OVER (
      PARTITION BY d.destinationairport
      ORDER BY d.distance NULLS LAST
    ) AS `rank`
    FROM `travel-sample`.inventory.route AS d
    LIMIT 7;
    Results
    [
      {
          "destinationairport": "AAE",
          "id": 10201,
          "rank": 0.25
      },
      {
          "destinationairport": "AAE",
          "id": 10190,
          "rank": 0.5
      },
      {
          "destinationairport": "AAE",
          "id": 10240,
          "rank": 0.75
      },
      {
          "destinationairport": "AAE",
          "id": 10136,
          "rank": 1
      },
      {
          "destinationairport": "AAL",
          "id": 14392,
          "rank": 0.3333333333333333
      },
      {
          "destinationairport": "AAL",
          "id": 14867,
          "rank": 0.6666666666666666
      },
      {
          "destinationairport": "AAL",
          "id": 22505,
          "rank": 1
      },
    ]

    DENSE_RANK()

    Description

    Returns the dense rank of the current object — that is, the number of distinct objects preceding this object in the current window partition, plus one.

    The objects are ordered by the window order clause. If any objects are tied, they will have the same rank.

    For this function, when any objects have the same rank, the rank of the next object will be consecutive, so there will not be a gap in the sequence of returned values. For example, if there are three objects ranked 2, the next dense rank is 3.

    Syntax

    dense-rank-function ::= DENSE_RANK '()' OVER ( '(' window-definition ')' | window-ref )
    'DENSE_RANK' '()' 'OVER' ( '(' window-definition ')' | window-ref )

    Arguments

    None.

    Window Specification

    The window specification may include an optional window partition clause, and must include a window order clause.

    Return Values

    An integer, greater than or equal to 1.

    Example

    For each country, find the dense rank of all airports in order of altitude.

    SELECT a.airportname, a.geo.alt, DENSE_RANK() OVER (
      PARTITION BY a.country
      ORDER BY a.geo.alt NULLS LAST
    ) AS `rank`
    FROM `travel-sample`.inventory.airport AS a
    LIMIT 10;
    Results
    [
      {
        "airportname": "Croisette Heliport",
        "alt": 0,
        "rank": 1
      },
      {
        "airportname": "Andernos-Les-Bains",
        "alt": 0,
        "rank": 1
      },
      {
        "airportname": "La Defense Heliport",
        "alt": 0,
        "rank": 1
      },
      {
        "airportname": "Marigot Bus Stop",
        "alt": 0,
        "rank": 1
      },
      {
        "airportname": "Lille",
        "alt": 1,
        "rank": 2
      },
      {
        "airportname": "Le Palyvestre",
        "alt": 7,
        "rank": 3
      },
      {
        "airportname": "Frejus Saint Raphael",
        "alt": 7,
        "rank": 3
      },
      {
        "airportname": "Calais Dunkerque",
        "alt": 12,
        "rank": 4
      },
      {
        "airportname": "Cote D\\'Azur",
        "alt": 12,
        "rank": 4
      },
      {
        "airportname": "Propriano",
        "alt": 13,
        "rank": 5
      }
    ]

    FIRST_VALUE(expr)

    Description

    Returns the requested value from the first object in the current window frame, where the window frame is determined by the window definition.

    Syntax

    first-value-function ::= FIRST_VALUE '(' expr ')' [ nulls-treatment ]
                             OVER ( '(' window-definition ')' | window-ref )
    'FIRST_VALUE' '(' expr ')' nulls-treatment? 'OVER' ( '(' window-definition ')' | window-ref )

    Arguments

    expr

    [Required] The value that you want to return from the first object in the window frame. [1]

    Nulls Modifier

    The nulls modifier determines how NULL or MISSING values are treated when finding the first object in the window frame:

    IGNORE NULLS

    If the values for any objects evaluate to NULL or MISSING, those objects are not included when finding the first object. In this case, the function returns the first non-NULL, non-MISSING value.

    RESPECT NULLS

    If the values for any objects evaluate to NULL or MISSING, those objects are included when finding the first object.

    If the nulls modifier is omitted, the default is RESPECT NULLS.

    Window Specification

    The window specification may include an optional window partition clause, an optional window order clause, and an optional window frame clause.

    Return Values

    The specified value from the first object.

    If all values are NULL or MISSING it returns NULL.

    In the following cases, this function may return unpredictable results.

    • If the window order clause is omitted.

    • If the window frame is defined by ROWS, and there are tied objects in the window frame.

    To make the function return deterministic results, add a window order clause, or add further ordering terms to the window order clause so that no objects are tied.

    If the window frame is defined by RANGE or GROUPS, and there are tied objects in the window frame, the function returns the lowest value of the input expression.

    Example

    Refer also to Example 3 in WINDOW Clause for a query showing this function used with the WINDOW clause.

    For each airport, show each route starting at that airport, including the distance of the route and the distance of the shortest route from that airport.

    SELECT r.sourceairport, r.destinationairport, r.distance,
    FIRST_VALUE(r.distance) OVER (
      PARTITION BY r.sourceairport
      ORDER BY r.distance
    ) AS `shortest_distance`
    FROM `travel-sample`.inventory.route AS r
    LIMIT 7;
    Results
    [
      {
          "destinationairport": "MRS",
          "distance": 767.6526005881392,
          "shortest_distance": 767.6526005881392,
          "sourceairport": "AAE"
      },
      {
          "destinationairport": "LYS",
          "distance": 1015.6529968903878,
          "shortest_distance": 767.6526005881392,
          "sourceairport": "AAE"
      },
      {
          "destinationairport": "ORY",
          "distance": 1395.3690007167947,
          "shortest_distance": 767.6526005881392,
          "sourceairport": "AAE"
      },
      {
          "destinationairport": "CDG",
          "distance": 1420.6731433915318,
          "shortest_distance": 767.6526005881392,
          "sourceairport": "AAE"
      },
      {
          "destinationairport": "AAR",
          "distance": 99.89861063028253,
          "shortest_distance": 99.89861063028253,
          "sourceairport": "AAL"
      },
      {
          "destinationairport": "OSL",
          "distance": 352.33081791745275,
          "shortest_distance": 99.89861063028253,
          "sourceairport": "AAL"
      },
      {
          "destinationairport": "LGW",
          "distance": 928.284226131001,
          "shortest_distance": 99.89861063028253,
          "sourceairport": "AAL"
      }
    ]

    LAG(expr [, offset [, default ] ] )

    Description

    Returns the value of an object at a given offset prior to the current object position.

    Syntax

    lag-function ::= LAG '(' expr [ ',' offset [ ',' default ] ] ')' [ nulls-treatment ]
                     OVER ( '(' window-definition ')' | window-ref )
    'LAG' '(' expr ( ',' offset ( ',' default )? )? ')' nulls-treatment? 'OVER' ( '(' window-definition ')' | window-ref )

    Arguments

    expr

    [Required] The value that you want to return from the offset object. [1]

    offset

    [Optional] A positive integer greater than 0. If omitted, the default is 1.

    default

    [Optional] The value to return when the offset goes out of window scope. If omitted, the default is NULL.

    Nulls Modifier

    The nulls modifier determines how NULL or MISSING values are treated when counting the offset:

    IGNORE NULLS

    If the values for any objects evaluate to NULL or MISSING, those objects are not included when counting the offset.

    RESPECT NULLS

    If the values for any objects evaluate to NULL or MISSING, those objects are included when counting the offset.

    If the nulls modifier is omitted, the default is RESPECT NULLS.

    Window Specification

    The window specification may include an optional window partition clause, and must include a window order clause.

    Return Values

    The specified value from the offset object.

    If the offset object is out of scope, it returns the default value, or NULL if no default is specified.

    Example

    Refer also to Example 1 in WINDOW Clause for a query showing this function used with the WINDOW clause.

    For each airline, show each route operated by that airline, including the length of the route and the length of the next-shortest route.

    SELECT r.airline, r.id, r.distance,
    LAG(r.distance, 1, "No previous distance") OVER (
      PARTITION BY r.airline
      ORDER BY r.distance NULLS LAST
    ) AS `previous-distance`
    FROM `travel-sample`.inventory.route AS r
    LIMIT 7;
    Results
    [
      {
          "airline": "2L",
          "distance": 770.9691328580009,
          "id": 125,
          "previous-distance": "No previous distance"
      },
      {
          "airline": "2L",
          "distance": 770.969132858001,
          "id": 117,
          "previous-distance": 770.9691328580009
      },
      {
          "airline": "2L",
          "distance": 922.7579695456559,
          "id": 118,
          "previous-distance": 770.969132858001
      },
      {
          "airline": "2L",
          "distance": 922.7579695456559,
          "id": 126,
          "previous-distance": 922.7579695456559
      },
      {
          "airline": "3F",
          "distance": 23.957943869396804,
          "id": 274,
          "previous-distance": "No previous distance"
      },
      {
          "airline": "3F",
          "distance": 23.957943869396804,
          "id": 276,
          "previous-distance": 23.957943869396804
      },
      {
          "airline": "3F",
          "distance": 26.397914084363418,
          "id": 282,
          "previous-distance": 23.957943869396804
      }
    ]

    LAST_VALUE(expr)

    Description

    Returns the requested value from the last object in the current window frame, where the window frame is specified by the window definition.

    Syntax

    last-value-function ::= LAST_VALUE '(' expr ')' [ nulls-treatment ]
                            OVER ( '(' window-definition ')' | window-ref )
    'LAST_VALUE' '(' expr ')' nulls-treatment? 'OVER' ( '(' window-definition ')' | window-ref )

    Arguments

    expr

    [Required] The value that you want to return from the last object in the window frame. [1]

    Nulls Modifier

    The nulls modifier determines how NULL or MISSING values are treated when finding the last object in the window frame:

    IGNORE NULLS

    If the values for any objects evaluate to NULL or MISSING, those objects are not included when finding the last object. In this case, the function returns the last non-NULL, non-MISSING value.

    RESPECT NULLS

    If the values for any objects evaluate to NULL or MISSING, those objects are included when finding the last object.

    If the nulls modifier is omitted, the default is RESPECT NULLS.

    Window Specification

    The window specification may include an optional window partition clause, an optional window order clause, and an optional window frame clause.

    Return Values

    The specified value from the last object.

    If all values are NULL or MISSING it returns NULL.

    In the following cases, this function may return unpredictable results.

    To make the function return deterministic results, add a window order clause, or add further ordering terms to the window order clause so that no objects are tied.

    If the window frame is defined by RANGE or GROUPS, and there are tied objects in the window frame, the function returns the highest value of the input expression.

    Example

    Refer also to Example 3 in WINDOW Clause for a query showing this function used with the WINDOW clause.

    For each airport, show each route starting at that airport, including the distance of the route and the distance of the longest route from that airport.

    SELECT r.sourceairport, r.destinationairport, r.distance,
    LAST_VALUE(r.distance) OVER (
      PARTITION BY r.sourceairport
      ORDER BY r.distance
      ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING (1)
    ) AS `longest_distance`
    FROM `travel-sample`.inventory.route AS r
    LIMIT 7;
    Results
    [
      {
          "destinationairport": "MRS",
          "distance": 767.6526005881392,
          "longest_distance": 1420.6731433915318,
          "sourceairport": "AAE"
      },
      {
          "destinationairport": "LYS",
          "distance": 1015.6529968903878,
          "longest_distance": 1420.6731433915318,
          "sourceairport": "AAE"
      },
      {
          "destinationairport": "ORY",
          "distance": 1395.3690007167947,
          "longest_distance": 1420.6731433915318,
          "sourceairport": "AAE"
      },
      {
          "destinationairport": "CDG",
          "distance": 1420.6731433915318,
          "longest_distance": 1420.6731433915318,
          "sourceairport": "AAE"
      },
      {
          "destinationairport": "AAR",
          "distance": 99.89861063028253,
          "longest_distance": 928.284226131001,
          "sourceairport": "AAL"
      },
      {
          "destinationairport": "OSL",
          "distance": 352.33081791745275,
          "longest_distance": 928.284226131001,
          "sourceairport": "AAL"
      },
      {
          "destinationairport": "LGW",
          "distance": 928.284226131001,
          "longest_distance": 928.284226131001,
          "sourceairport": "AAL"
      }
    ]
    1 This clause specifies that the window frame should extend to the end of the window partition. Without this clause, the end point of the window frame would always be the current object. This would mean that the longest distance would always be the same as the current distance.

    LEAD(expr [, offset [, default ] ] )

    Description

    Returns the value of an object at a given offset ahead of the current object position.

    Syntax

    lead-function ::= LEAD '(' expr [ ',' offset [ ',' default ] ] ')' [ nulls-treatment ]
                      OVER ( '(' window-definition ')' | window-ref )
    'LEAD' '(' expr ( ',' offset ( ',' default )? )? ')' nulls-treatment? 'OVER' ( '(' window-definition ')' | window-ref )

    Arguments

    expr

    [Required] The value that you want to return from the offset object. [1]

    offset

    [Optional] A positive integer greater than 0. If omitted, the default is 1.

    default

    [Optional] The value to return when the offset goes out of window scope. If omitted, the default is NULL.

    Nulls Modifier

    The nulls modifier determines how NULL or MISSING values are treated when counting the offset:

    IGNORE NULLS

    If the values for any objects evaluate to NULL or MISSING, those objects are not included when counting the offset.

    RESPECT NULLS

    If the values for any objects evaluate to NULL or MISSING, those objects are included when counting the offset.

    If the nulls modifier is omitted, the default is RESPECT NULLS.

    Window Specification

    The window specification may include an optional window partition clause, and must include a window order clause.

    Return Values

    The specified value from the offset object.

    If the offset object is out of scope, it returns the default value, or NULL if no default is specified.

    Example

    Refer also to Example 1 in WINDOW Clause for a query showing this function used with the WINDOW clause.

    For each airline, show each route operated by that airline, including the length of the route and the length of the next-longest route.

    SELECT r.airline, r.id, r.distance,
    LEAD(r.distance, 1, "No next distance") OVER (
      PARTITION BY r.airline
      ORDER BY r.distance NULLS LAST
    ) AS `next-distance`
    FROM `travel-sample`.inventory.route AS r
    LIMIT 7;
    Results
      [
      {
          "airline": "2L",
          "distance": 770.9691328580009,
          "id": 125,
          "next-distance": 770.969132858001
      },
      {
          "airline": "2L",
          "distance": 770.969132858001,
          "id": 117,
          "next-distance": 922.7579695456559
      },
      {
          "airline": "2L",
          "distance": 922.7579695456559,
          "id": 118,
          "next-distance": 922.7579695456559
      },
      {
          "airline": "2L",
          "distance": 922.7579695456559,
          "id": 126,
          "next-distance": "No next distance"
      },
      {
          "airline": "3F",
          "distance": 23.957943869396804,
          "id": 274,
          "next-distance": 23.957943869396804
      },
      {
          "airline": "3F",
          "distance": 23.957943869396804,
          "id": 276,
          "next-distance": 26.397914084363418
      },
      {
          "airline": "3F",
          "distance": 26.397914084363418,
          "id": 282,
          "next-distance": 26.397914084363418
      }
    ]

    NTH_VALUE(expr, offset)

    Description

    Returns the requested value from an object in the current window frame, where the window frame is specified by the window definition.

    Syntax

    nth-value-function ::= NTH_VALUE '(' expr ',' offset ')' [ nthval-from ] [ nulls-treatment ]
                           OVER ( '(' window-definition ')' | window-ref )
    'NTH_VALUE' '(' expr ',' offset ')' nth-val-from? nulls-treatment? 'OVER' ( '(' window-definition ')' | window-ref )

    Arguments

    expr

    [Required] The value that you want to return from the offset object in the window frame. [1]

    offset

    [Required] The number of the offset object within the window frame, counting from 1.

    From Modifier

    The from modifier determines where the function starts counting the offset.

    FROM FIRST

    Offset counting starts at the first object in the window frame. In this case, an offset of 1 is the first object in the window frame, 2 is the second object, and so on.

    FROM LAST

    Offset counting starts at the last object in the window frame. In this case, an offset of 1 is the last object in the window frame, 2 is the second-to-last object, and so on.

    Nulls Modifier

    The nulls modifier determines how NULL or MISSING values are treated when counting the offset:

    IGNORE NULLS

    If the values for any objects evaluate to NULL or MISSING, those objects are not included when counting the offset.

    RESPECT NULLS

    If the values for any objects evaluate to NULL or MISSING, those objects are included when counting the offset.

    If the nulls modifier is omitted, the default is RESPECT NULLS.

    Window Specification

    The window specification may include an optional window partition clause, an optional window order clause, and an optional window frame clause.

    Return Values

    The specified value from the offset object.

    In the following cases, this function may return unpredictable results.

    To make the function return deterministic results, add a window order clause, or add further ordering terms to the window order clause so that no objects are tied.

    If the window frame is defined by RANGE or GROUPS, and there are tied objects in the window frame, the function returns the lowest value of the input expression when counting FROM FIRST, or the highest value of the input expression when counting FROM LAST.

    Examples

    For each airport, show each route starting at that airport, including the distance of the route and the distance of the second shortest route from that airport.

    SELECT r.sourceairport, r.destinationairport, r.distance,
    NTH_VALUE(r.distance, 2) FROM FIRST OVER (
      PARTITION BY r.sourceairport
      ORDER BY r.distance
      ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING (1)
    ) AS `shortest_distance_but_1`
    FROM `travel-sample`.inventory.route AS r
    LIMIT 7;
    Results
    [
      {
          "destinationairport": "MRS",
          "distance": 767.6526005881392,
          "shortest_distance_but_1": 1015.6529968903878,
          "sourceairport": "AAE"
      },
      {
          "destinationairport": "LYS", (2)
          "distance": 1015.6529968903878,
          "shortest_distance_but_1": 1015.6529968903878,
          "sourceairport": "AAE"
      },
      {
          "destinationairport": "ORY",
          "distance": 1395.3690007167947,
          "shortest_distance_but_1": 1015.6529968903878,
          "sourceairport": "AAE"
      },
      {
          "destinationairport": "CDG",
          "distance": 1420.6731433915318,
          "shortest_distance_but_1": 1015.6529968903878,
          "sourceairport": "AAE"
      },
      {
          "destinationairport": "AAR",
          "distance": 99.89861063028253,
          "shortest_distance_but_1": 352.33081791745275,
          "sourceairport": "AAL"
      },
      {
          "destinationairport": "OSL", (2)
          "distance": 352.33081791745275,
          "shortest_distance_but_1": 352.33081791745275,
          "sourceairport": "AAL"
      },
      {
          "destinationairport": "LGW",
          "distance": 928.284226131001,
          "shortest_distance_but_1": 352.33081791745275,
          "sourceairport": "AAL"
      }
    ]
    1 This clause specifies that the window frame should extend to the end of the window partition. Without this clause, the end point of the window frame would always be the current object. This would mean that for the route with the shortest distance, the function would be unable to find the route with the second shortest distance.
    2 The route with the second shortest distance from this airport.

    For each airport, show each route starting at that airport, including the distance of the route and the distance of the second longest route from that airport.

    SELECT r.sourceairport, r.destinationairport, r.distance,
    NTH_VALUE(r.distance, 2) FROM LAST OVER (
      PARTITION BY r.sourceairport
      ORDER BY r.distance
      ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING (1)
    ) AS `longest_distance_but_1`
    FROM `travel-sample`.inventory.route AS r
    LIMIT 7;
    Results
    [
      {
          "destinationairport": "MRS",
          "distance": 767.6526005881392,
          "longest_distance_but_1": 1395.3690007167947,
          "sourceairport": "AAE"
      },
      {
          "destinationairport": "LYS",
          "distance": 1015.6529968903878,
          "longest_distance_but_1": 1395.3690007167947,
          "sourceairport": "AAE"
      },
      {
          "destinationairport": "ORY",
          "distance": 1395.3690007167947,
          "longest_distance_but_1": 1395.3690007167947, (2)
          "sourceairport": "AAE"
      },
      {
          "destinationairport": "CDG",
          "distance": 1420.6731433915318,
          "longest_distance_but_1": 1395.3690007167947,
          "sourceairport": "AAE"
      },
      {
          "destinationairport": "AAR",
          "distance": 99.89861063028253,
          "longest_distance_but_1": 352.33081791745275,
          "sourceairport": "AAL"
      },
      {
          "destinationairport": "OSL",
          "distance": 352.33081791745275,
          "longest_distance_but_1": 352.33081791745275, (2)
          "sourceairport": "AAL"
      },
      {
          "destinationairport": "LGW",
          "distance": 928.284226131001,
          "longest_distance_but_1": 352.33081791745275,
          "sourceairport": "AAL"
      }
    ]
    1 This clause specifies that the window frame should extend to the end of the window partition. Without this clause, the end point of the window frame would always be the current object. This would mean the function would be unable to find the route with the second longest distance for routes with shorter distances.
    2 The route with the second longest distance from this airport.

    NTILE(num_tiles)

    Description

    Divides the window partition into the specified number of tiles, and allocates each object in the window partition to a tile, so that as far as possible each tile has an equal number of objects. When the set of objects is not equally divisible by the number of tiles, the function puts more objects into the lower-numbered tiles. For each object, the function returns the number of the tile into which that object was placed.

    Syntax

    ntile-function ::= NTILE '(' num_tiles ')' OVER ( '(' window-definition ')' | window-ref )
    'NTILE' '(' num_tiles ')' 'OVER' ( '(' window-definition ')' | window-ref )

    Arguments

    num_tiles

    [Required] The number of tiles into which you want to divide the window partition. This argument can be an expression and must evaluate to a number. If the number is not an integer, it will be truncated. If the expression depends on an object, it evaluates from the first object in the window partition.

    Window Specification

    The window specification may include an optional window partition clause, and must include a window order clause.

    Return Values

    An value greater than or equal to 1 and less than or equal to the number of tiles.

    Example

    For each airline, allocate each route to one of three tiles by distance.

    SELECT r.airline, r.distance, NTILE(3) OVER (
      PARTITION BY r.airline
      ORDER BY r.distance
    ) AS `ntile`
    FROM `travel-sample`.inventory.route AS r
    LIMIT 16;
    Results
    [
      {
        "airline": "2L",
        "distance": 770.9691328580009,
        "ntile": 1
      },
      {
        "airline": "2L",
        "distance": 770.969132858001,
        "ntile": 1
      },
      {
        "airline": "2L",
        "distance": 922.7579695456559,
        "ntile": 2
      },
      {
        "airline": "2L",
        "distance": 922.7579695456559,
        "ntile": 3
      },
      {
        "airline": "3F",
        "distance": 23.957943869396804,
        "ntile": 1
      },
      {
        "airline": "3F",
        "distance": 23.957943869396804,
        "ntile": 1
      },
      {
        "airline": "3F",
        "distance": 26.397914084363418,
        "ntile": 1
      },
      {
        "airline": "3F",
        "distance": 26.397914084363418,
        "ntile": 1
      },
      {
        "airline": "3F",
        "distance": 31.613003135476145,
        "ntile": 2
      },
      {
        "airline": "3F",
        "distance": 31.613003135476145,
        "ntile": 2
      },
      {
        "airline": "3F",
        "distance": 60.49012512494272,
        "ntile": 2
      },
      {
        "airline": "3F",
        "distance": 60.490125124942736,
        "ntile": 2
      },
      {
        "airline": "3F",
        "distance": 63.640308584677314,
        "ntile": 3
      },
      {
        "airline": "3F",
        "distance": 63.640308584677314,
        "ntile": 3
      },
      {
        "airline": "3F",
        "distance": 91.53839302649642,
        "ntile": 3
      },
      {
        "airline": "3F",
        "distance": 91.53839302649642,
        "ntile": 3
      }
    ]

    PERCENT_RANK()

    Description

    Returns the percentile rank of the current object — that is, the rank of the object minus one, divided by the total number of objects in the window partition minus one.

    Syntax

    percent-rank-function ::= PERCENT_RANK '()' OVER ( '(' window-definition ')' | window-ref )
    'PERCENT_RANK' '()' 'OVER' ( '(' window-definition ')' | window-ref )

    Arguments

    None.

    Window Specification

    The window specification may include an optional window partition clause, and must include a window order clause.

    Return Values

    A number between 0 and 1. The higher the value, the higher the ranking.

    Example

    For each destination airport, find the percentile rank of all routes in order of distance.

    SELECT d.id, d.destinationairport, PERCENT_RANK() OVER (
      PARTITION BY d.destinationairport
      ORDER BY d.distance NULLS LAST
    ) AS `rank`
    FROM `travel-sample`.inventory.route AS d
    LIMIT 7;
    Results
    [
      {
          "destinationairport": "AAE",
          "id": 10201,
          "rank": 0
      },
      {
          "destinationairport": "AAE",
          "id": 10190,
          "rank": 0.3333333333333333
      },
      {
          "destinationairport": "AAE",
          "id": 10240,
          "rank": 0.6666666666666666
      },
      {
          "destinationairport": "AAE",
          "id": 10136,
          "rank": 1
      },
      {
          "destinationairport": "AAL",
          "id": 14392,
          "rank": 0
      },
      {
          "destinationairport": "AAL",
          "id": 14867,
          "rank": 0.5
      },
      {
          "destinationairport": "AAL",
          "id": 22505,
          "rank": 1
      }
    ]

    RANK()

    Description

    Returns the rank of the current object — that is, the number of distinct objects preceding this object in the current window partition, plus one.

    The objects are ordered by the window order clause. If any objects are tied, they will have the same rank.

    When any objects have the same rank, the rank of the next object will include all preceding objects, so there may be a gap in the sequence of returned values. For example, if there are three objects ranked 2, the next rank is 5.

    Syntax

    rank-function ::= RANK '()' OVER ( '(' window-definition ')' | window-ref )
    'RANK' '()' 'OVER' ( '(' window-definition ')' | window-ref )

    Arguments

    None.

    Window Specification

    The window specification may include an optional window partition clause, and must include a window order clause.

    Return Values

    An integer, greater than or equal to 1.

    Example

    For each country, find the rank of all airports in order of altitude.

    SELECT a.airportname, a.geo.alt, RANK() OVER (
      PARTITION BY a.country
      ORDER BY a.geo.alt NULLS LAST
    ) AS `rank`
    FROM `travel-sample`.inventory.airport AS a
    LIMIT 10;
    Results
    [
      {
        "airportname": "Croisette Heliport",
        "alt": 0,
        "rank": 1
      },
      {
        "airportname": "Andernos-Les-Bains",
        "alt": 0,
        "rank": 1
      },
      {
        "airportname": "La Defense Heliport",
        "alt": 0,
        "rank": 1
      },
      {
        "airportname": "Marigot Bus Stop",
        "alt": 0,
        "rank": 1
      },
      {
        "airportname": "Lille",
        "alt": 1,
        "rank": 5
      },
      {
        "airportname": "Le Palyvestre",
        "alt": 7,
        "rank": 6
      },
      {
        "airportname": "Frejus Saint Raphael",
        "alt": 7,
        "rank": 6
      },
      {
        "airportname": "Calais Dunkerque",
        "alt": 12,
        "rank": 8
      },
      {
        "airportname": "Cote D\\'Azur",
        "alt": 12,
        "rank": 8
      },
      {
        "airportname": "Propriano",
        "alt": 13,
        "rank": 10
      }
    ]

    RATIO_TO_REPORT(expr)

    Description

    Returns the fractional ratio of the specified value for each object to the sum of values for all objects in the window frame. If the window frame clause is not specified, the fractional ratio is calculated for the whole window partition.

    Syntax

    ratio-to-report-function ::= RATIO_TO_REPORT '(' expr ')'
                                 OVER ( '(' window-definition ')' | window-ref )
    'RATIO_TO_REPORT' '(' expr ')' 'OVER' ( '(' window-definition ')' | window-ref )

    Arguments

    expr

    [Required] The value for which you want to calculate the fractional ratio. [1]

    Window Specification

    The window specification may include an optional window partition clause, an optional window order clause, and an optional window frame clause.

    Return Values

    A number between 0 and 1, representing the fractional ratio of the value for the current object to the sum of values for all objects in the current window frame. The sum of values for all objects in the current window frame is 1.

    If the input expression does not evaluate to a number, or the sum of values for all objects is zero, it returns NULL.

    Example

    Refer also to Example 2 in WINDOW Clause for a query showing this function used with the WINDOW clause.

    For each destination airport, calculate the distance of each route as a fraction of the total distance of all routes.

    SELECT d.id, d.destinationairport, RATIO_TO_REPORT(d.distance) OVER (
      PARTITION BY d.destinationairport
    ) AS `distance-ratio`
    FROM `travel-sample`.inventory.route AS d
    LIMIT 7;
    Results
    [
      {
          "destinationairport": "AAE",
          "distance-ratio": 0.3088857862487639,
          "id": 10136
      },
      {
          "destinationairport": "AAE",
          "distance-ratio": 0.22082544177013463,
          "id": 10190
      },
      {
          "destinationairport": "AAE",
          "distance-ratio": 0.3033841055547952,
          "id": 10240
      },
      {
          "destinationairport": "AAE",
          "distance-ratio": 0.16690466642630636,
          "id": 10201
      },
      {
          "destinationairport": "AAL",
          "distance-ratio": 0.25521719160354467,
          "id": 14867
      },
      {
          "destinationairport": "AAL",
          "distance-ratio": 0.6724194454614251,
          "id": 22505
      },
      {
          "destinationairport": "AAL",
          "distance-ratio": 0.07236336293503035,
          "id": 14392
      }
    ]

    ROW_NUMBER()

    Description

    Returns a unique row number for every object in every window partition. In each window partition, the row numbering starts at 1.

    The window order clause determines the sort order of the objects. If the window order clause is omitted, the return values may be unpredictable.

    Syntax

    row-number-function ::= ROW_NUMBER '()'  OVER ( '(' window-definition ')' | window-ref )
    'ROW_NUMBER' '()'  'OVER' ( '(' window-definition ')' | window-ref )

    Arguments

    None.

    Window Specification

    The window specification may include an optional window partition clause, and an optional window order clause.

    Return Values

    An integer, greater than or equal to 1.

    Example

    Refer also to Example 2 in WINDOW Clause for a query showing this function used with the WINDOW clause.

    For each destination airport, number all routes in order of distance.

    SELECT d.id, d.destinationairport, ROW_NUMBER() OVER (
      PARTITION BY d.destinationairport
      ORDER BY d.distance NULLS LAST
    ) AS `row`
    FROM `travel-sample`.inventory.route AS d
    LIMIT 7;
    Results
    [
      {
        "destinationairport": "AAE",
        "id": 10201,
        "row": 1
      },
      {
        "destinationairport": "AAE",
        "id": 10190,
        "row": 2
      },
      {
        "destinationairport": "AAE",
        "id": 10240,
        "row": 3
      },
      {
        "destinationairport": "AAE",
        "id": 10136,
        "row": 4
      },
      {
        "destinationairport": "AAL",
        "id": 14392,
        "row": 1
      },
      {
        "destinationairport": "AAL",
        "id": 14867,
        "row": 2
      },
      {
        "destinationairport": "AAL",
        "id": 22505,
        "row": 3
      }
    ]

    1. If the query contains the GROUP BY clause or aggregate functions, this expression must only depend on GROUP BY expressions or aggregate functions.