How do I batch sql statements with package database/sql

Question

How do I batch sql statements with Go\'s database/sql package?

In Java I would do it like this :

// Create a prepared statement
String sql = \"INSERT         


        

Answer 1

In case anyone is using pgx (the supposed best Postgres driver in Golang), see this solution: https://github.com/jackc/pgx/issues/764#issuecomment-685249471

Answer 2

Batching is not possible via the interfaces available in database/sql. A particular database driver may support it separately, however. For instance https://github.com/ziutek/mymysql appears to support batching with MySQL.

Answer 3

Since the db.Exec function is variadic, one option (that actually does only make a single network roundtrip) is to construct the statement yourself and explode the arguments and pass them in.

Sample code:

func BulkInsert(unsavedRows []*ExampleRowStruct) error {
    valueStrings := make([]string, 0, len(unsavedRows))
    valueArgs := make([]interface{}, 0, len(unsavedRows) * 3)
    for _, post := range unsavedRows {
        valueStrings = append(valueStrings, "(?, ?, ?)")
        valueArgs = append(valueArgs, post.Column1)
        valueArgs = append(valueArgs, post.Column2)
        valueArgs = append(valueArgs, post.Column3)
    }
    stmt := fmt.Sprintf("INSERT INTO my_sample_table (column1, column2, column3) VALUES %s", 
                        strings.Join(valueStrings, ","))
    _, err := db.Exec(stmt, valueArgs...)
    return err
}

In a simple test I ran, this solution is about 4 times faster at inserting 10,000 rows than the Begin, Prepare, Commit presented in the other answer - though the actual improvement will depend a lot on your individual setup, network latencies, etc.

Answer 4

If you’re using PostgreSQL then pq supports bulk imports.

Answer 5

Adapting Andrew's solution for PostgreSQL, which doesn't support the ? placeholder, the following works:

func BulkInsert(unsavedRows []*ExampleRowStruct) error {
    valueStrings := make([]string, 0, len(unsavedRows))
    valueArgs := make([]interface{}, 0, len(unsavedRows) * 3)
    i := 0
    for _, post := range unsavedRows {
        valueStrings = append(valueStrings, fmt.Sprintf("($%d, $%d, $%d)", i*3+1, i*3+2, i*3+3))
        valueArgs = append(valueArgs, post.Column1)
        valueArgs = append(valueArgs, post.Column2)
        valueArgs = append(valueArgs, post.Column3)
        i++
    }
    stmt := fmt.Sprintf("INSERT INTO my_sample_table (column1, column2, column3) VALUES %s", strings.Join(valueStrings, ","))
    _, err := db.Exec(stmt, valueArgs...)
    return err
}

Answer 6

Here's a more generic version to generate the query & value args based on answers from @andrew-c and @mastercarl:

// bulk/insert.go

import (
    "strconv"
    "strings"
)

type ValueExtractor = func(int) []interface{}

func Generate(tableName string, columns []string, numRows int, postgres bool, valueExtractor ValueExtractor) (string, []interface{}) {
    numCols := len(columns)
    var queryBuilder strings.Builder
    queryBuilder.WriteString("INSERT INTO ")
    queryBuilder.WriteString(tableName)
    queryBuilder.WriteString("(")
    for i, column := range columns {
        queryBuilder.WriteString("\"")
        queryBuilder.WriteString(column)
        queryBuilder.WriteString("\"")
        if i < numCols-1 {
            queryBuilder.WriteString(",")
        }
    }
    queryBuilder.WriteString(") VALUES ")
    var valueArgs []interface{}
    valueArgs = make([]interface{}, 0, numRows*numCols)
    for rowIndex := 0; rowIndex < numRows; rowIndex++ {
        queryBuilder.WriteString("(")
        for colIndex := 0; colIndex < numCols; colIndex++ {
            if postgres {
                queryBuilder.WriteString("$")
                queryBuilder.WriteString(strconv.Itoa(rowIndex*numCols + colIndex + 1))
            } else {
                queryBuilder.WriteString("?")
            }
            if colIndex < numCols-1 {
                queryBuilder.WriteString(",")
            }
        }
        queryBuilder.WriteString(")")
        if rowIndex < numRows-1 {
            queryBuilder.WriteString(",")
        }
        valueArgs = append(valueArgs, valueExtractor(rowIndex)...)
    }
    return queryBuilder.String(), valueArgs
}

// bulk/insert_test.go

import (
    "fmt"
    "strconv"
)

func valueExtractor(index int) []interface{} {
    return []interface{}{
        "trx-" + strconv.Itoa(index),
        "name-" + strconv.Itoa(index),
        index,
    }
}

func ExampleGeneratePostgres() {
    query, valueArgs := Generate("tbl_persons", []string{"transaction_id", "name", "age"}, 3, true, valueExtractor)
    fmt.Println(query)
    fmt.Println(valueArgs)
    // Output:
    // INSERT INTO tbl_persons("transaction_id","name","age") VALUES ($1,$2,$3),($4,$5,$6),($7,$8,$9)
    // [[trx-0 name-0 0] [trx-1 name-1 1] [trx-2 name-2 2]]
}

func ExampleGenerateOthers() {
    query, valueArgs := Generate("tbl_persons", []string{"transaction_id", "name", "age"}, 3, false, valueExtractor)
    fmt.Println(query)
    fmt.Println(valueArgs)
    // Output:
    // INSERT INTO tbl_persons("transaction_id","name","age") VALUES (?,?,?),(?,?,?),(?,?,?)
    // [[trx-0 name-0 0] [trx-1 name-1 1] [trx-2 name-2 2]]
}