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Implement explain query plan #77

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Jun 20, 2022
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Implement explain query plan #77

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41 changes: 35 additions & 6 deletions lib/ecto/adapters/sqlite3/connection.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -319,15 +319,48 @@ defmodule Ecto.Adapters.SQLite3.Connection do

@impl true
def explain_query(conn, query, params, opts) do
case query(conn, build_explain_query(query), params, opts) do
type = Keyword.get(opts, :type, :query_plan)

case query(conn, build_explain_query(query, type), params, opts) do
{:ok, %Exqlite.Result{} = result} ->
{:ok, SQL.format_table(result)}
case type do
:query_plan -> {:ok, format_query_plan_explain(result)}
:instructions -> {:ok, SQL.format_table(result)}
end

error ->
error
end
end

defp build_explain_query(query, :query_plan) do
IO.iodata_to_binary(["EXPLAIN QUERY PLAN", query])
end

defp build_explain_query(query, :instructions) do
IO.iodata_to_binary(["EXPLAIN ", query])
end

# Mimics the ASCII format of the sqlite CLI
defp format_query_plan_explain(%{rows: rows}) do
{lines, _} =
rows
|> Enum.chunk_every(2, 1, [nil])
|> Enum.map_reduce(0, fn [[id, parent, _, text], next], depth ->
{branch, next_depth} =
case {id, parent, next} do
{id, _, [_, id, _, _]} -> {"|--", depth + 1}
{_, p, [_, p, _, _]} -> {"|--", depth}
_ -> {"`--", depth - 1}
end

formatted_line = String.duplicate("| ", depth) <> branch <> text
{formatted_line, next_depth}
end)

Enum.join(["QUERY PLAN" | lines], "\n")
end

##
## DDL
##
Expand Down Expand Up @@ -654,10 +687,6 @@ defmodule Ecto.Adapters.SQLite3.Connection do
{"SELECT name FROM sqlite_master WHERE type='table' AND name=? LIMIT 1", [table]}
end

def build_explain_query(query) do
IO.iodata_to_binary(["EXPLAIN ", query])
end

##
## Query generation
##
Expand Down