When using a foreign table (e.g. a mysql table) clickhouse doesn't seem to properly send the result of functions if they are called inside `WHERE` statements.

Executing `SELECT foo FROM foreign_table WHERE a=10 AND b='2019-10-05'` will send a statement like:

```
SELECT `foo`, `a`, `b` FROM `db`.`foreign_table`  WHERE (`a` = 10) AND (`b` = '2019-10-05')
```

But executing `SELECT foo FROM foreign_table WHERE a=10 AND b=toDate('2019-10-05')` will send:

```
SELECT `foo`, `a`, `b` FROM `db`.`foreign_table`  WHERE (`a` = 10)
```

I assume that the function is executed afterwards and `b` is parsed clickhouse-side.

I'm not sure if there is an easy fix for this, but I assume this would help with the efficiency of mysql foreign tables and might be critical in some high-load scenarios where one wants to filter on indexed columns.

My specific issue here is different and relates to the clickhouse mindsdb integration, but I think this "bug" (if you'd call it such) is more generic.
{
    const State & state = State::instance();
    check(state, 1,
          "SELECT column FROM test.table WHERE (1,1) IN ((1,1))",
          R"(SELECT "column" FROM "test"."table" WHERE 1 = 1)");
    check(state, 1,
          "SELECT field, value FROM test.table WHERE (field, value) IN (('foo', 'bar'))",
          R"(SELECT "field", "value" FROM "test"."table" WHERE ("field", "value") IN (('foo', 'bar')))");
}
TEST(TransformQueryForExternalDatabase, InWithTable)
{
    const State & state = State::instance();
    check(state, 1,
          "SELECT column FROM test.table WHERE 1 IN external_table",
          R"(SELECT "column" FROM "test"."table")");
    check(state, 1,
          "SELECT column FROM test.table WHERE 1 IN (x)",
          R"(SELECT "column" FROM "test"."table")");
    check(state, 1,
          "SELECT column, field, value FROM test.table WHERE column IN (field, value)",
          R"(SELECT "column", "field", "value" FROM "test"."table" WHERE "column" IN ("field", "value"))");
    check(state, 1,
          "SELECT column FROM test.table WHERE column NOT IN hello AND column = 123",
          R"(SELECT "column" FROM "test"."table" WHERE "column" = 123)");
}
TEST(TransformQueryForExternalDatabase, Like)