Use raw queries for table_exists? check

lib/ecto/adapters/mysql/connection.ex

@@ -716,15 +716,7 @@ if Code.ensure_loaded?(Mariaex) do
 
     @impl true
     def table_exists_query(table) do
-      require Ecto.Query
-
-      Ecto.Query.from(
-        t in "tables",
-        prefix: "information_schema",
-        where: t.table_name == ^table and t.table_schema == fragment("DATABASE()"),
-        select: t.table_name,
-        limit: 1
-      )
+      {"SELECT true FROM information_schema.tables WHERE table_name = ? AND table_schema = DATABASE() LIMIT 1", [table]}
     end
 
     defp pk_definitions(columns, prefix) do

lib/ecto/adapters/myxql/connection.ex

@@ -703,15 +703,7 @@ if Code.ensure_loaded?(MyXQL) do
 
     @impl true
     def table_exists_query(table) do
-      require Ecto.Query
-
-      Ecto.Query.from(
-        t in "tables",
-        prefix: "information_schema",
-        where: t.table_name == ^table and t.table_schema == fragment("DATABASE()"),
-        select: t.table_name,
-        limit: 1
-      )
+      {"SELECT true FROM information_schema.tables WHERE table_name = ? AND table_schema = DATABASE() LIMIT 1", [table]}
     end
 
     defp pk_definitions(columns, prefix) do

lib/ecto/adapters/postgres/connection.ex

@@ -801,15 +801,7 @@ if Code.ensure_loaded?(Postgrex) do
 
     @impl true
     def table_exists_query(table) do
-      require Ecto.Query
-
-      Ecto.Query.from(
-        t in "tables",
-        prefix: "information_schema",
-        where: t.table_name == ^table and t.table_schema == fragment("current_schema()"),
-        select: t.table_name,
-        limit: 1
-      )
+      {"SELECT true FROM information_schema.tables WHERE table_name = $1 AND table_schema = current_schema() LIMIT 1", [table]}
     end
 
     # From https://www.postgresql.org/docs/9.3/static/protocol-error-fields.html.

lib/ecto/adapters/sql.ex

@@ -359,15 +359,13 @@ defmodule Ecto.Adapters.SQL do
   Check if the given `table` exists.
 
   Returns `true` if the `table` exists in the `repo`, otherwise `false`.
+  The table is checked against the current database/schema in the connection.
   """
   @spec table_exists?(Ecto.Repo.t, table :: String.t) :: boolean
   def table_exists?(repo, table) when is_atom(repo) do
-    table_exists?(repo, Ecto.Adapter.lookup_meta(repo), table)
-  end
-
-  defp table_exists?(repo, %{sql: sql}, table) do
-    sql_query = sql.table_exists_query(table)
-    repo.one(sql_query) != nil
+    %{sql: sql} = adapter_meta = Ecto.Adapter.lookup_meta(repo)
+    {query, params} = sql.table_exists_query(table)
+    query!(adapter_meta, query, params, []).num_rows != 0
   end
 
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