Javascript 仅当名称和位置不'；不匹配

我只尝试在psql表中添加一条记录，如果它具有唯一的名称和位置。如果条目在表（名称或位置）中不存在，则可以插入记录，但如果名称已经存在，则我的服务器会在响应查询时抛出错误。这是我目前的代码：

app.post("/addCampground", async (req, res) => {
    const name = req.body.name;

    const location = req.body.location;
    const leng = req.body.maxlength;
    const elev = req.body.elevation;
    const site = req.body.sites;
    const pad = req.body.pad;

try{
    
const template = "INSERT INTO campgrounds (name, location, maxlength, elevation,
 sites, padtype) VALUES ($1, $2, $3, $4, $5, $6) SELECT name, location WHERE NOT 
EXISTS(SELECT name, location from campgrounds where name =$1 AND location =$2) ";
console.log(template);
const response = await pool.query(template, [name, location, leng, elev, site,
 pad], [name, location]);

res.json({status: "added", results:{name:name, location:location} });
}catch (err){
    res.json({status: "campground already in database"});
}

})

问题是：

const template = "INSERT INTO campgrounds (name, location, maxlength, elevation, sites, padtype) VALUES
 ($1, $2, $3, $4, $5, $6) SELECT name, location WHERE NOT EXISTS(SELECT name, location from campgrounds
 where name =$1 AND location =$2) ";

const response = await pool.query(template, [name, location, leng, elev, site, pad], [name, location]);

尝试添加具有匹配名称但位置不同的记录时出错：

TypeError: cb is not a function
    at Query.callback (/home/sbeg/db-class-350/practice/task4/node_modules/pg-pool/index.js:376:18)
    at Query.handleError (/home/sbeg/db-class-350/practice/task4/node_modules/pg/lib/query.js:128:19)
    at Client._handleErrorMessage (/home/sbeg/db-class-350/practice/task4/node_modules/pg/lib/client.js:335:17)
    at Connection.emit (events.js:315:20)
    at /home/sbeg/db-class-350/practice/task4/node_modules/pg/lib/connection.js:115:12
    at Parser.parse (/home/sbeg/db-class-350/practice/task4/node_modules/pg-protocol/dist/parser.js:40:17)
    at Socket.<anonymous> (/home/sbeg/db-class-350/practice/task4/node_modules/pg-protocol/dist/index.js:10:42)
    at Socket.emit (events.js:315:20)
    at addChunk (_stream_readable.js:295:12)
    at readableAddChunk (_stream_readable.js:271:9)

TypeError:cb不是函数
在Query.callback（/home/sbeg/db-class-350/practice/task4/node_modules/pg pool/index.js:376:18）
在Query.handleError（/home/sbeg/db-class-350/practice/task4/node_modules/pg/lib/Query.js:128:19）
在客户端处理错误消息（/home/sbeg/db-class-350/practice/task4/node_modules/pg/lib/Client.js:335:17）
在Connection.emit（events.js:315:20）
at/home/sbeg/db-class-350/practice/task4/node_modules/pg/lib/connection.js:115:12
在Parser.parse（/home/sbeg/db-class-350/practice/task4/node_modules/pg protocol/dist/Parser.js:40:17）
在插座上。（/home/sbeg/db-class-350/practice/task4/node_modules/pg protocol/dist/index.js:10:42）
在Socket.emit（events.js:315:20）
在addChunk（_stream_readable.js:295:12）
在readableAddChunk（_stream_readable.js:271:9）

sql的正确语法：

INSERT INTO campgrounds (name, location, maxlength, elevation, sites, padtype) 
SELECT ($1, $2, $3, $4, $5, $6)
WHERE NOT EXISTS(SELECT 1 from campgrounds where name =$1 AND location =$2)

或者，如果名称、位置列上有唯一索引，则可以在Conflict上使用

：

INSERT INTO campgrounds (name, location, maxlength, elevation, sites, padtype) 
VALUES ($1, $2, $3, $4, $5, $6) ON CONFLICT unique_index DO NOTHING

在insert语句中不能同时使用值和SELECT。看起来你应该使用插入。。。冲突。是否类似于“在冲突中插入营地（名称、位置、最大长度、标高、场地、焊盘类型）值（$1、$2、$3、$4、$5、$6）不执行任何操作”？如果我将其更改为此，则不会插入任何内容