Make constant a string generated from a function in F# - f#

Question

I am new to F# and I have been pulling my hair out from this question:
The SqlCommandProvider requires a constant string which I am unable to provide by the below function.
Running it in F# interactive returns "This is not a valid constant expression or custom attribute value. "
let textgen (RIC: string, price: float, volume: int, inst: int, time:string) =
let mutable mystring = "INSERT INTO hsbc(RIC, price, volume, type, time) VALUES (st1, st2, st3, st4, st5)"
mystring <- mystring.Replace ("st1", RIC)
mystring <- mystring.Replace ("st2", price.ToString())
mystring <- mystring.Replace ("st3", volume.ToString())
mystring <- mystring.Replace ("st4", inst.ToString())
mystring <- mystring.Replace ("st5", time)
mystring
let sqlcommand1 = textgen("0005.hk",71.2,5000,1,"2019-07-18 10:34:09.193")
type writedata4=SqlCommandProvider<sqlcommand1,connStr>
do
let cmd6 = new writedata4(connStr)
cmd6.Execute()
0
I have done some research and know that this is a problem with sqlcommand1 not being a constant during compile time. So I tried this:
[<Literal>]
let sqlcommand1 = textgen("0005.hk",71.2,5000,1,"2019-07-18 10:34:09.193")
which again returns: "This is not a valid constant expression or custom attribute value"
Any help would be appreciated, many thanks!
Update:
thanks! I adapted the code from #Mark Pattison and this works:
let mywrite(RIC: string, price: float, volume: int, inst: int, time:string) =
use cmd99 = new SqlCommandProvider<"INSERT INTO hsbc(RIC, price, volume, type, time) VALUES (#st1, #st2, #st3, #st4, #st5)", connStr>(connStr)
cmd99.Execute(st1=RIC,st2=price,st3=volume,st4=inst,st5=System.DateTime.Parse time)
|> ignore
however, the official docs does mention:
let cmd = new SqlCommandProvider<const(SqlFile<"GetDate.sql">.Text), connStr>(connStr)
cmd.Execute() |> ignore
Since the command is loaded from an external text, there should be even less compile time certainty and shouldn't work (but it appears to work).
Can you please tell me why? Thanks

Answer 1

The idea is that the command text is a compile-time constant. Clearly your sqlcommand1 can't be, as it's created at runtime by calling textgen.
Here's an example of how to create a parametrised command using #, from the docs:
open FSharp.Data
[<Literal>]
let connectionString =
#"Data Source=.;Initial Catalog=AdventureWorks2012;Integrated Security=True"
do
use cmd = new SqlCommandProvider<"
SELECT TOP(#topN) FirstName, LastName, SalesYTD
FROM Sales.vSalesPerson
WHERE CountryRegionName = #regionName AND SalesYTD > #salesMoreThan
ORDER BY SalesYTD
" , connectionString>(connectionString)
cmd.Execute(topN = 3L, regionName = "United States", salesMoreThan = 1000000M) |> printfn "%A"
//output
//seq
// [("Pamela", "Ansman-Wolfe", 1352577.1325M);
// ("David", "Campbell", 1573012.9383M);
// ("Tete", "Mensa-Annan", 1576562.1966M)]
You can see that the command string itself (starting SELECT...) is a constant string.