将占位符与copy和pg-query-stream一起使用

问题描述

我正在尝试将查询提取为csv文件。我试图将copy与pg-query-stream一起使用来执行查询，但是我遇到了这个错误：

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

从查询中删除copy时，如果我提供的查询带有copy且没有占位符，则该占位符也可以正常工作。

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

解决方法

COPY上下文中有一个限制，它禁止您使用任何参数。

但是您可以使用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']);

我认为您正在将两个功能混在一起。

pg-query-stream将这些行作为流返回，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即可。

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)

如果要使用copy，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)

javascript pg-promise postgresql