CODEWITHSUNDEEP
postgresqlselectgorows
joshlf
joshlf

Reputation: 23547

Postgres SELECT in Go returns all columns as string (using pq and database/sql)

I'm doing a select in Go using the database/sql package and the pq Postgres driver:

rows, err := db.Query("SELECT (name, age) FROM people WHERE id = 1")

I tried retrieving the values in the normal way:

rows.Next()
name := ""
age := 0
err = rows.Scan(&name, &age)

but I got the error:

sql: expected 1 destination arguments in Scan, not 2

The documentation for sql.(*Rows).Scan says that you can pass a byte slice pointer and it will be filled with the raw results. So I did this:

b := make([]byte, 1024*1024)
rows.Scan(&b)
fmt.Println(string(b))

which succeeded, printing:

(John,18)

So I looked at the source code for sql.(*Rows).Scan, and it turns out that the error is returned if the number of arguments doesn't match the number of results returned by the database driver (which makes sense). So, for some reason, the pq driver seems to be returning the result set as a single value. Why would this be?

Upvotes: 7

Views: 4795

Answers (2)

jabclab
jabclab

Reputation: 15042

When using a function with out parameters which only ever returns one row I was running into the same issue. The following resolved it for me:

var foo, bar string
err := db.QueryRow("select * from my_function()").Scan(&foo, &bar)

The function was of this form:

create or replace function my_function(
  out first_out varchar,
  out second_out json
) as $$
  -- etc.
$$ language plpgsql;

Upvotes: 2

joshlf
joshlf

Reputation: 23547

Thanks to a_horse_with_no_name for the right answer! I'm posting it here for ... posterity?

In Postgres, doing SELECT (a, b) with parentheses returns a single record, which is an anonymous composite type. Removing the parentheses will return the columns individually: Select a, b.

Upvotes: 6

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