windowfuncs.c

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/*-------------------------------------------------------------------------
 *
 * windowfuncs.c
 *    Standard window functions defined in SQL spec.
 *
 * Portions Copyright (c) 2000-2013, PostgreSQL Global Development Group
 *
 *
 * IDENTIFICATION
 *    src/backend/utils/adt/windowfuncs.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "utils/builtins.h"
#include "windowapi.h"

/*
 * ranking process information
 */
typedef struct rank_context
{
    int64       rank;           /* current rank */
} rank_context;

/*
 * ntile process information
 */
typedef struct
{
    int32       ntile;          /* current result */
    int64       rows_per_bucket;    /* row number of current bucket */
    int64       boundary;       /* how many rows should be in the bucket */
    int64       remainder;      /* (total rows) % (bucket num) */
} ntile_context;

static bool rank_up(WindowObject winobj);
static Datum leadlag_common(FunctionCallInfo fcinfo,
               bool forward, bool withoffset, bool withdefault);


/*
 * utility routine for *_rank functions.
 */
static bool
rank_up(WindowObject winobj)
{
    bool        up = false;     /* should rank increase? */
    int64       curpos = WinGetCurrentPosition(winobj);
    rank_context *context;

    context = (rank_context *)
        WinGetPartitionLocalMemory(winobj, sizeof(rank_context));

    if (context->rank == 0)
    {
        /* first call: rank of first row is always 1 */
        Assert(curpos == 0);
        context->rank = 1;
    }
    else
    {
        Assert(curpos > 0);
        /* do current and prior tuples match by ORDER BY clause? */
        if (!WinRowsArePeers(winobj, curpos - 1, curpos))
            up = true;
    }

    /* We can advance the mark, but only *after* acccess to prior row */
    WinSetMarkPosition(winobj, curpos);

    return up;
}


/*
 * row_number
 * just increment up from 1 until current partition finishes.
 */
Datum
window_row_number(PG_FUNCTION_ARGS)
{
    WindowObject winobj = PG_WINDOW_OBJECT();
    int64       curpos = WinGetCurrentPosition(winobj);

    WinSetMarkPosition(winobj, curpos);
    PG_RETURN_INT64(curpos + 1);
}


/*
 * rank
 * Rank changes when key columns change.
 * The new rank number is the current row number.
 */
Datum
window_rank(PG_FUNCTION_ARGS)
{
    WindowObject winobj = PG_WINDOW_OBJECT();
    rank_context *context;
    bool        up;

    up = rank_up(winobj);
    context = (rank_context *)
        WinGetPartitionLocalMemory(winobj, sizeof(rank_context));
    if (up)
        context->rank = WinGetCurrentPosition(winobj) + 1;

    PG_RETURN_INT64(context->rank);
}

/*
 * dense_rank
 * Rank increases by 1 when key columns change.
 */
Datum
window_dense_rank(PG_FUNCTION_ARGS)
{
    WindowObject winobj = PG_WINDOW_OBJECT();
    rank_context *context;
    bool        up;

    up = rank_up(winobj);
    context = (rank_context *)
        WinGetPartitionLocalMemory(winobj, sizeof(rank_context));
    if (up)
        context->rank++;

    PG_RETURN_INT64(context->rank);
}

/*
 * percent_rank
 * return fraction between 0 and 1 inclusive,
 * which is described as (RK - 1) / (NR - 1), where RK is the current row's
 * rank and NR is the total number of rows, per spec.
 */
Datum
window_percent_rank(PG_FUNCTION_ARGS)
{
    WindowObject winobj = PG_WINDOW_OBJECT();
    rank_context *context;
    bool        up;
    int64       totalrows = WinGetPartitionRowCount(winobj);

    Assert(totalrows > 0);

    up = rank_up(winobj);
    context = (rank_context *)
        WinGetPartitionLocalMemory(winobj, sizeof(rank_context));
    if (up)
        context->rank = WinGetCurrentPosition(winobj) + 1;

    /* return zero if there's only one row, per spec */
    if (totalrows <= 1)
        PG_RETURN_FLOAT8(0.0);

    PG_RETURN_FLOAT8((float8) (context->rank - 1) / (float8) (totalrows - 1));
}

/*
 * cume_dist
 * return fraction betweeen 0 and 1 inclusive,
 * which is described as NP / NR, where NP is the number of rows preceding or
 * peers to the current row, and NR is the total number of rows, per spec.
 */
Datum
window_cume_dist(PG_FUNCTION_ARGS)
{
    WindowObject winobj = PG_WINDOW_OBJECT();
    rank_context *context;
    bool        up;
    int64       totalrows = WinGetPartitionRowCount(winobj);

    Assert(totalrows > 0);

    up = rank_up(winobj);
    context = (rank_context *)
        WinGetPartitionLocalMemory(winobj, sizeof(rank_context));
    if (up || context->rank == 1)
    {
        /*
         * The current row is not peer to prior row or is just the first, so
         * count up the number of rows that are peer to the current.
         */
        int64       row;

        context->rank = WinGetCurrentPosition(winobj) + 1;

        /*
         * start from current + 1
         */
        for (row = context->rank; row < totalrows; row++)
        {
            if (!WinRowsArePeers(winobj, row - 1, row))
                break;
            context->rank++;
        }
    }

    PG_RETURN_FLOAT8((float8) context->rank / (float8) totalrows);
}

/*
 * ntile
 * compute an exact numeric value with scale 0 (zero),
 * ranging from 1 (one) to n, per spec.
 */
Datum
window_ntile(PG_FUNCTION_ARGS)
{
    WindowObject winobj = PG_WINDOW_OBJECT();
    ntile_context *context;

    context = (ntile_context *)
        WinGetPartitionLocalMemory(winobj, sizeof(ntile_context));

    if (context->ntile == 0)
    {
        /* first call */
        int64       total;
        int32       nbuckets;
        bool        isnull;

        total = WinGetPartitionRowCount(winobj);
        nbuckets = DatumGetInt32(WinGetFuncArgCurrent(winobj, 0, &isnull));

        /*
         * per spec: If NT is the null value, then the result is the null
         * value.
         */
        if (isnull)
            PG_RETURN_NULL();

        /*
         * per spec: If NT is less than or equal to 0 (zero), then an
         * exception condition is raised.
         */
        if (nbuckets <= 0)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_ARGUMENT_FOR_NTILE),
                     errmsg("argument of ntile must be greater than zero")));

        context->ntile = 1;
        context->rows_per_bucket = 0;
        context->boundary = total / nbuckets;
        if (context->boundary <= 0)
            context->boundary = 1;
        else
        {
            /*
             * If the total number is not divisible, add 1 row to leading
             * buckets.
             */
            context->remainder = total % nbuckets;
            if (context->remainder != 0)
                context->boundary++;
        }
    }

    context->rows_per_bucket++;
    if (context->boundary < context->rows_per_bucket)
    {
        /* ntile up */
        if (context->remainder != 0 && context->ntile == context->remainder)
        {
            context->remainder = 0;
            context->boundary -= 1;
        }
        context->ntile += 1;
        context->rows_per_bucket = 1;
    }

    PG_RETURN_INT32(context->ntile);
}

/*
 * leadlag_common
 * common operation of lead() and lag()
 * For lead() forward is true, whereas for lag() it is false.
 * withoffset indicates we have an offset second argument.
 * withdefault indicates we have a default third argument.
 */
static Datum
leadlag_common(FunctionCallInfo fcinfo,
               bool forward, bool withoffset, bool withdefault)
{
    WindowObject winobj = PG_WINDOW_OBJECT();
    int32       offset;
    bool        const_offset;
    Datum       result;
    bool        isnull;
    bool        isout;

    if (withoffset)
    {
        offset = DatumGetInt32(WinGetFuncArgCurrent(winobj, 1, &isnull));
        if (isnull)
            PG_RETURN_NULL();
        const_offset = get_fn_expr_arg_stable(fcinfo->flinfo, 1);
    }
    else
    {
        offset = 1;
        const_offset = true;
    }

    result = WinGetFuncArgInPartition(winobj, 0,
                                      (forward ? offset : -offset),
                                      WINDOW_SEEK_CURRENT,
                                      const_offset,
                                      &isnull, &isout);

    if (isout)
    {
        /*
         * target row is out of the partition; supply default value if
         * provided.  otherwise it'll stay NULL
         */
        if (withdefault)
            result = WinGetFuncArgCurrent(winobj, 2, &isnull);
    }

    if (isnull)
        PG_RETURN_NULL();

    PG_RETURN_DATUM(result);
}

/*
 * lag
 * returns the value of VE evaluated on a row that is 1
 * row before the current row within a partition,
 * per spec.
 */
Datum
window_lag(PG_FUNCTION_ARGS)
{
    return leadlag_common(fcinfo, false, false, false);
}

/*
 * lag_with_offset
 * returns the value of VE evelulated on a row that is OFFSET
 * rows before the current row within a partition,
 * per spec.
 */
Datum
window_lag_with_offset(PG_FUNCTION_ARGS)
{
    return leadlag_common(fcinfo, false, true, false);
}

/*
 * lag_with_offset_and_default
 * same as lag_with_offset but accepts default value
 * as its third argument.
 */
Datum
window_lag_with_offset_and_default(PG_FUNCTION_ARGS)
{
    return leadlag_common(fcinfo, false, true, true);
}

/*
 * lead
 * returns the value of VE evaluated on a row that is 1
 * row after the current row within a partition,
 * per spec.
 */
Datum
window_lead(PG_FUNCTION_ARGS)
{
    return leadlag_common(fcinfo, true, false, false);
}

/*
 * lead_with_offset
 * returns the value of VE evaluated on a row that is OFFSET
 * number of rows after the current row within a partition,
 * per spec.
 */
Datum
window_lead_with_offset(PG_FUNCTION_ARGS)
{
    return leadlag_common(fcinfo, true, true, false);
}

/*
 * lead_with_offset_and_default
 * same as lead_with_offset but accepts default value
 * as its third argument.
 */
Datum
window_lead_with_offset_and_default(PG_FUNCTION_ARGS)
{
    return leadlag_common(fcinfo, true, true, true);
}

/*
 * first_value
 * return the value of VE evaluated on the first row of the
 * window frame, per spec.
 */
Datum
window_first_value(PG_FUNCTION_ARGS)
{
    WindowObject winobj = PG_WINDOW_OBJECT();
    Datum       result;
    bool        isnull;

    result = WinGetFuncArgInFrame(winobj, 0,
                                  0, WINDOW_SEEK_HEAD, true,
                                  &isnull, NULL);
    if (isnull)
        PG_RETURN_NULL();

    PG_RETURN_DATUM(result);
}

/*
 * last_value
 * return the value of VE evaluated on the last row of the
 * window frame, per spec.
 */
Datum
window_last_value(PG_FUNCTION_ARGS)
{
    WindowObject winobj = PG_WINDOW_OBJECT();
    Datum       result;
    bool        isnull;

    result = WinGetFuncArgInFrame(winobj, 0,
                                  0, WINDOW_SEEK_TAIL, true,
                                  &isnull, NULL);
    if (isnull)
        PG_RETURN_NULL();

    PG_RETURN_DATUM(result);
}

/*
 * nth_value
 * return the value of VE evaluated on the n-th row from the first
 * row of the window frame, per spec.
 */
Datum
window_nth_value(PG_FUNCTION_ARGS)
{
    WindowObject winobj = PG_WINDOW_OBJECT();
    bool        const_offset;
    Datum       result;
    bool        isnull;
    int32       nth;

    nth = DatumGetInt32(WinGetFuncArgCurrent(winobj, 1, &isnull));
    if (isnull)
        PG_RETURN_NULL();
    const_offset = get_fn_expr_arg_stable(fcinfo->flinfo, 1);

    if (nth <= 0)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_ARGUMENT_FOR_NTH_VALUE),
                 errmsg("argument of nth_value must be greater than zero")));

    result = WinGetFuncArgInFrame(winobj, 0,
                                  nth - 1, WINDOW_SEEK_HEAD, const_offset,
                                  &isnull, NULL);
    if (isnull)
        PG_RETURN_NULL();

    PG_RETURN_DATUM(result);
}