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exosql

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Universal SQL engine for Elixir. This library implements the SQL logic to perform queries on user provided databases using a simple interface based on Foreign Data Wrappers from PostgreSQL.

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exosql lib builtins.ex
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lib/builtins.ex 

require Logger



defmodule ExoSQL.Builtins do

  @moduledoc """

  Builtin functions.



  There are two categories, normal functions and aggregate functions. Aggregate

  functions receive as first parameter a ExoSQL.Result with a full table,

  and the rest of parameters are the function calling parameters, unsolved.



  These expressions must be first simplified with

  `ExoSQL.executor.simplify_expr_columns` and then executed on the rows with

  `ExoSQL.Expr.run_expr`.

  """

  import ExoSQL.Utils, only: [to_number: 1, to_float: 1]



  def round(n, r) do

    {:ok, n} = to_float(n)

    {:ok, r} = to_number(r)



    Float.round(n, r)

  end



  def concat(a, b) do

    a = to_string(a)

    b = to_string(b)



    a <> b

  end



  def not_(a) do

    not bool(a)

  end



  def bool(nil), do: false

  def bool(0), do: false

  def bool(""), do: false

  def bool(false), do: false

  def bool(_), do: true



  def lower(s), do: String.downcase(s)

  def upper(s), do: String.upcase(s)

  def to_string_(s), do: to_string(s)



  ### Aggregate functions

  def is_aggregate("count"), do: true

  def is_aggregate("avg"), do: true

  def is_aggregate("sum"), do: true

  def is_aggregate(_other), do: false



  def count(data, _) do

  # Logger.debug("Count #{inspect data}")

    Enum.count(data.rows)

  end



  def avg(data, expr) do

  # Logger.debug("Avg of #{inspect data} by #{inspect expr}")

    sum(data, expr) / count(data, nil)

  end



  def sum(data, expr) do

  # Logger.debug("Sum of #{inspect data} by #{inspect expr}")

    expr = ExoSQL.Executor.simplify_expr_columns(expr, data.columns)

    # Logger.debug("Simplified expression #{inspect expr}")

    Enum.reduce(data.rows, 0, fn row, acc ->

      n = ExoSQL.Expr.run_expr(expr, row)

      {:ok, n} = ExoSQL.Utils.to_number(n)

      acc + n

    end)

  end

end