## sql.to_sql()


SQL for a Substrait JSON plan, with the semantics `Rel.eval` gives it.


Usage

``` python
sql.to_sql(
    plan,
    dialect,
    *,
    deterministic=False,
    guards=True,
    unchecked=None,
    finite=True,
    tie_free=None
)
```


The result has the plan's output names (`RelRoot.names`, else `c0`, …), and is ordered as Lean orders it when the plan has a FETCH or a window. Raises [Unsupported](sql.Unsupported.md#sverify.sql.Unsupported) for plans outside the Lean model. This is [sverify.engines.to_sql](engines.to_sql.md#sverify.engines.to_sql).

`deterministic=True` promises that no two rows tie on any window's PARTITION BY and ORDER BY columns (what a contract report's `deterministic` says, and what `Report.run(deterministic=True)` requires). Then windows need no ordinal tiebreak, so engines without a stable scan order can run them; FETCH still needs one.

`guards=False` leaves out the run-time checks ([Dialect.guards](sql.Dialect.md#sverify.sql.Dialect.guards)). Only pass it for a plan whose contract report is `guard_free`, and run the SQL on data that meets the contract's preconditions.

`unchecked` leaves them out of some expressions only: pass a contract report's `unchecked` for the same plan, and run the SQL on data that meets its preconditions (`Rel.evalG_marks`). The other expressions, and every aggregate, keep their checks.


## Parameters


`plan: dict | str`  
A Substrait JSON plan, as a string or parsed (`json.loads`), such as a node's [internal_plan](Node.internal_plan.md#sverify.Node.internal_plan) or [sverify.engines.written_plan](engines.written_plan.md#sverify.engines.written_plan)'s output.

`dialect: Dialect`  
The engine to write SQL for: [sverify.engines.DUCKDB](engines.DUCKDB.md#sverify.engines.DUCKDB), [sverify.engines.SNOWFLAKE](engines.SNOWFLAKE.md#sverify.engines.SNOWFLAKE) or [sverify.engines.SPARK](engines.SPARK.md#sverify.engines.SPARK).

`deterministic: bool = ``False`  
Promise that windows have no ties on their PARTITION BY and ORDER BY columns (`Report.deterministic`). Default: False.

`guards: bool = ``True`  
Write the run-time checks. Default: True.

`unchecked: dict | None = None`  
The expressions to write without checks, as a contract report's `unchecked` (`sverify.Report.unchecked`) for this plan. Default: None (all of them keep their checks).

`finite: bool = ``True`  
Write the check that finite doubles do not overflow to `±∞` ([Dialect.finite](sql.Dialect.md#sverify.sql.Dialect.finite)), the reference's precondition (#575). Default: True; False for a plan verified with `semantics="duckdb"`.

`tie_free: bool | None = None`  
Deprecated alias of `deterministic`.


## Returns


`str`  
One SQL query in the dialect. It reads the plan's tables by their

names, quoted.


## Raises


`Unsupported`  
The plan is outside the Lean model, its root names do not match its columns, the dialect cannot express it, or `unchecked` is for another plan.


## Examples

The plan of a transform, as Snowflake SQL:

``` python
import json

import pyarrow as pa
import sverify as sv
from sverify.engines import SNOWFLAKE, to_sql
from sverify.io import StaticSource

orders = StaticSource(pa.table({"id": [1, 2], "amount": [30, 5]}), name="orders")


@sv.transform()
def big_orders(orders):
    return orders.filter(orders.amount > 10)


print(to_sql(big_orders(orders).internal_plan, SNOWFLAKE))
# SELECT s1."c0" AS "id", s1."c1" AS "amount" FROM (SELECT s2."c0" AS "c0", ...
```