Null support for civil.*

[El-76]

Is your feature request related to a problem? Please describe.
civil.* types support lacks nullable types, so its impossible to pass NULL value of say, civil.DateTime type, as OUT parameter.

Describe the solution you'd like
Add Nullable counterparts for civil.* types to the driver.

Describe alternatives you've considered
Passing sql.NullTime and converting to civil.*

Additional context
I could add the support myself if provided with some guidelines on how to do.

[shueybubbles]

let's see if the robot can do it.

[shueybubbles]

@El-76 is #290 what you are looking for? are there any other tests to add in that PR to cover your specific use cases?

[El-76]

WoW! I feel old and useless...

At the first glance TVP support is broken.

This code:

package main

import (
	"fmt"
	"database/sql"
	"os"

	"github.com/golang-sql/civil"
	mssql "github.com/microsoft/go-mssqldb"
)

type tvpDataRow struct {
	T mssql.NullDateTime
}

func main() {
	tvpData := []tvpDataRow{
		{
			T: mssql.NullDateTime{},
		},
	}

	tvpType := mssql.TVP{
		TypeName: "dbo.TableValueParameterType",
		Value: tvpData,
	}

	dsn := "sqlserver://sa:<pass>@127.0.0.1:1435?database=test"

	db, err := sql.Open("sqlserver", dsn)

	if err != nil {
		fmt.Printf("Error opening databaase connection: %s\n", err.Error())

		os.Exit(1)
	}

	defer db.Close()

	rows, err := db.Query("exec dbo.test_tvp @Rows", sql.Named("Rows", tvpType))

	if err != nil {
		fmt.Printf("Error querying stored procedure: %s\n", err.Error())

		os.Exit(1)
	}

	t := civil.DateTime{}

	rows.Next()

	rows.Scan(&t)
}

fails with

Error querying stored procedure: mssql: The incoming tabular data stream (TDS) remote procedure call (RPC) protocol stream is incorrect. Table-valued parameter 0 (""), row 0, column 0: Data type 0x1F is unknown.

And this one:

package main

import (
	"fmt"
	"database/sql"
	"os"

	"github.com/golang-sql/civil"
	mssql "github.com/microsoft/go-mssqldb"
)

type tvpDataRow struct {
	T mssql.NullDateTime
}

func main() {
	t1, _ := civil.ParseDateTime("2025-10-02t16:10:55")

	tvpData := []tvpDataRow{
		{
			T: mssql.NullDateTime{DateTime: t1, Valid: true},
		},
	}

	tvpType := mssql.TVP{
		TypeName: "dbo.TableValueParameterType",
		Value: tvpData,
	}

	dsn := "sqlserver://sa:<pass>@127.0.0.1:1435?database=test"

	db, err := sql.Open("sqlserver", dsn)

	if err != nil {
		fmt.Printf("Error opening databaase connection: %s\n", err.Error())

		os.Exit(1)
	}

	defer db.Close()

	rows, err := db.Query("exec dbo.test_tvp @Rows", sql.Named("Rows", tvpType))

	if err != nil {
		fmt.Printf("Error querying stored procedure: %s\n", err.Error())

		os.Exit(1)
	}

	t := civil.DateTime{}

	rows.Next()

	rows.Scan(&t)
}

with

Error querying stored procedure: failed to make tvp parameter row col: non-Value type civil.DateTime returned from Value

Table / type / procedure definitions are:

CREATE TABLE res (
    T DATETIME NULL
)
GO

CREATE TYPE TableValueParameterType AS TABLE (
    T DATETIME NULL
)
GO

CREATE OR ALTER PROCEDURE test_tvp
    @Rows dbo.TableValueParameterType READONLY
AS
BEGIN
    SELECT T FROM @Rows

    INSERT INTO res SELECT T FROM @Rows
END
GO

I could fix both (and review the other stuff) based on the solution the robot provided if you don't object.

[shueybubbles]

@El-76 you could either take Copilot's code as a starter for your own PR or I can literally paste the code you gave in this comment as a comment in the existing PR and tell copilot to fix the TVP issues and see how it does.
Just let me know.

[El-76]

Hm, lets give the robot its chance :) - really interesting to see the outcome.

[shueybubbles]

@El-76 Sadly, the robot has run into a wall.
it might be worthwhile to look at what it did and fix the issues in a separate PR.

[El-76]

@shueybubbles oh, I'll take the initial branch as a base then file a PR. However, could you please take a look at #287 first - I expect conflicts with this one if merged.