使用带有 copy 和 pg-query-stream 的占位符

Question

我正在尝试将查询提取为 csv 文件。我尝试使用copy 和pg-query-stream 来执行查询，但我遇到了这个错误：

error: bind message supplies 1 parameters, but prepared statement "" requires 0

当从查询中删除 copy 时，如果我提供带有 copy 的查询并且没有占位符，它也可以与占位符一起正常工作。

const pgp = require('pg-promise')
const QueryStream = require('pg-query-stream')
query1 = "copy (select * from real_state WHERE town_code= $1 ) TO  '/tmp/file.csv'"
const qs = new QueryStream(query1, [22])
await db.stream(qs, s => {
            // initiate streaming into the console:
            s.pipe(JSONStream.stringify()).pipe(process.stdout)
        }).then(data => {
        }).catch(error => {
            console.log('ERROR:', error)
        })

---

query1 = "copy (select * from real_state WHERE town_code= $1 ) TO  '/tmp/file.csv'" ==> error
query2 = "copy (select * from real_state) TO  '/tmp/file.csv'" ==> It works
query3 = "select * from real_state WHERE town_code= $1" ==>  It works

Answer 1

COPY 上下文中有一个限制，禁止您使用任何参数。

但您可以使用pg-promise 查询格式来解决该限制：

const query = pgp.as.format('COPY(SELECT * FROM real_state WHERE town_code = $1) TO $2',
                            [22, '/tmp/file.csv']);

Answer 2

我认为您将两个功能混合在一起。

pg-query-stream 将行作为流返回，不需要在 select 中使用 copy。只需使用简单的选择，然后将结果通过管道传输到文件流。

const fs = require('fs')
const { Pool } = require('pg')
const QueryStream = require('pg-query-stream')

const query = new QueryStream("select * from real_state WHERE town_code= $1", [22]
const stream = pool.query(query)
const fileStream = fs.createReadStream('/tmp/file.csv')
fileStream.pipe(stream)

如果您想使用复制，请使用 pg-copy-streams：https://github.com/brianc/node-pg-copy-streams

const fs = require('fs')
const { Pool } = require('pg')
const copyFrom = require('pg-copy-streams').from
const stream = db.query(copyFrom('COPY real_state FROM stdin WHERE town_code= $1', [22])
const fileStream = fs.createReadStream('/tmp/file.csv')

fileStream.pipe(stream)