Add a Render() function which returns a valid query

[chrismwendt]

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Check this out:

q := sqlf.Sprintf("SELECT * FROM repos WHERE name = $1", "github.com/keegancsmith/sqlf")
fmt.Println(q.Render(sqlf.PostgresBindVar))

That prints this:

SELECT * FROM repos WHERE name = 'github.com/keegancsmith/sqlf'

Ready to copy-n-paste into psql, or EXPLAIN ANALYZE .... and print the timing info for local dev.

This was the bare minimum necessary to work for my pursposes, but there's a lot left to do in order to work in general for all BindVars, drivers, and argument types.

[chrismwendt]

I've been using this locally behind a debug flag while working on Rockskip. I'm not 100% sure the escape function is safe (so I removed the code that ran the query automatically).

I didn't expect this to get merged without a lot more work, and it should've been a draft to begin with.