如何检查表是否存在？[副本]

Question

const { Pool } = require('pg'); //node-postgres
const pool = new Pool;

module.exports = {
    query: (text, params, callback) => {
        return pool.query(text,params,callback);
    }
};

const db = require('./db/index');

    db.query('SELECT count(*) from pg_class where relname ="session" and relkind="r"', (err, res) => {
        if (err) {
          //TODO: What to do if there is an error?
        }
        console.log(res);
    });

如何检查名称为“session”的表是否存在？我如何知道我的查询是否有效？

编辑：这不是上述问题的重复，因为我的问题与Node.js javascript代码有关。不是SQL！我只想知道在res对象中查找什么，因为它似乎是未定义的...

Answer 1

你可以检查下面的代码；

SELECT EXISTS (
   SELECT 1
   FROM   information_schema.tables 
   WHERE  table_schema = 'schema_name'
   AND    table_name = 'table_name'
   );

或

SELECT EXISTS (
   SELECT 1 
   FROM   pg_catalog.pg_class c
   JOIN   pg_catalog.pg_namespace n ON n.oid = c.relnamespace
   WHERE  n.nspname = 'schema_name'
   AND    c.relname = 'table_name'
   );

或

SELECT 'schema_name.table_name'::regclass

SELECT to_regclass('schema_name.table_name');