仅当名称和位置不匹配时才插入答案

【问题标题】：INSERT INTO only if Name and Location DON'T match仅当名称和位置不匹配时才插入
【发布时间】：2021-04-14 15:51:37
【问题描述】：

我试图只在我的 psql 表中添加一条记录，如果它具有唯一的名称和位置。如果表中不存在条目（名称或位置），它可以插入记录，但如果名称已经存在，我的服务器会抛出错误以响应查询。到目前为止，这是我的代码：

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"});
}

})

有问题的查询是：

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]);

尝试添加名称匹配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)

【问题讨论】：

您不能在插入语句中同时使用 VALUES 和 SELECT。看来您应该使用 INSERT... ON CONFLICT。
会不会像“在冲突中唯一不做任何事情的情况下插入露营地（名称、位置、最大长度、海拔、地点、垫型）值（1 美元、2 美元、3 美元、4 美元、5 美元、6 美元）” ?如果我将其更改为此，则不会插入任何内容

标签： javascript sql postgresql postman psql

【解决方案1】：

正确的 sql 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，如果您对名称、位置列有唯一索引，则可以使用on confflict：

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

【讨论】：