Bulk INSERT in Postgres in GO using pgx


I am trying to bulk insert keys in db in go here is the code
Key Struct

type tempKey struct {
keyVal  string
lastKey int


Test Keys

data := []tempKey{
    {keyVal: "abc", lastKey: 10},
    {keyVal: "dns", lastKey: 11},
    {keyVal: "qwe", lastKey: 12},
    {keyVal: "dss", lastKey: 13},
    {keyVal: "xcmk", lastKey: 14},

Insertion part

dbUrl := "db url...."
conn, err := pgx.Connect(context.Background(), dbUrl)
if err != nil {
defer conn.Close(context.Background())
sqlStr := "INSERT INTO keys (keyval,lastval) VALUES "
dollars := ""
vals := []interface{}{}
count := 1
for _, row := range data {
    dollars = fmt.Sprintf("%s($%d, $%d),", dollars, count, count+1)
    vals = append(vals, row.keyVal, row.lastKey)
    count += 2
sqlStr += dollars
sqlStr = sqlStr[0 : len(sqlStr)-1]
fmt.Printf("%s \n", sqlStr)

_, erro := conn.Exec(context.Background(), sqlStr, vals)
if erro != nil {
    fmt.Fprint(os.Stderr, "Error : \n", erro)

on running it throws error: expected 10 arguments, got 1

What is the correct way of bulk inserting.


You are crafting the SQL statement by hand, which is fine, but you are not leveraging pgx which can help with this (see below).

Appending to the SQL string like so can be inefficient for large inputs

dollars = fmt.Sprintf("%s($%d, $%d),", dollars, count, count+1)

but also the final value has a trailing , where instead you need a termination character ; to indicate the end of the statement.

BTW this string truncation line is redundant:

sqlStr = sqlStr[0 : len(sqlStr)-1] // this is a NOOP

Anyway, better to use something more performant like strings.Builder when crafting long strings.

From the pgx docs, use pgx.Conn.CopyFrom:

func (c *Conn) CopyFrom(tableName Identifier, columnNames []string, rowSrc CopyFromSource) (int, error)

CopyFrom uses the PostgreSQL copy protocol to perform bulk data
insertion. It returns the number of rows copied and an error.

example usage of Copy:

rows := [][]interface{}{
    {"John", "Smith", int32(36)},
    {"Jane", "Doe", int32(29)},

copyCount, err := conn.CopyFrom(
    []string{"first_name", "last_name", "age"},

Answered By – colm.anseo

Answer Checked By – Clifford M. (GoLangFix Volunteer)

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