Primary and foreign keys and select statements

 create database classss;

use classss;


Create table temp (id int not null,name varchar(50),primary key(id));

create table temp2 (custid int ,name varchar(30),foreign key(custid) references temp(id));

insert into temp (id,name) values

(1,"abhi"),(2,"bhu");

insert into temp2 (custid,name) values (1,"soap"),(2,"brush");

select * from temp;

select * from temp2;

select id from temp;

select distinct name from temp2;



Comments

Post a Comment

Popular posts from this blog

DATABASE RELATIONSHIPS

Image
 RELATIONSHIPS INCLUDE  ONE - TO -ONE (1x 1)   ONE ENTITY OF A TABLE IS IN RELATION WITH ONLY ONE ENTITY OF ANOTHER. ONE - TO -MANY (1x N)   ONE ENTITY IS IN RELATION WITH MANY MANY - TO - MANY(NxN)   MANY ENTITIES ARE IN RELATION WITH MANY OTHER. ONE- TO-MANY IS MORE HARDER TO BE REPRESENTED THAN ONE - TO - ONE AND MANY - TO - MANY ONE- TO -MANY IT IS CATEGORIZED INTO 3 BASED ON MANY MANY CAN BE IN 3 TYPES 1. ONE -TO-FEW:  SMALL NUMBER (2,5 ,100,500) STORE THE CHILD DOCUMENT INSIDE PARENT TAKE ZOMATO OR AMAZON FOR EXAMPLE, A SINGLE USER CAN HAVE MULTIPLE ADDRESSES. HERE WE DONOT CREATE TWO MODELS FOR USER AND ADDRESS, AS ADDRESS IS ASSOCIATED WITH USER DIRECTILY, WE STORE THE CHILD DOCUMENT INSIDE PARENT. const mongoose = require ( "mongoose" ); const { Schema } = mongoose ; main ()   . then (() => {     console . log ( "connection successful" );   })   . catch (( err ) => {     console . log ( err );...
Read more

ROUTING (GET /) home route

Image
  app . get ( "/" , ( req , res ) => {   let q = 'SELECT COUNT(*) FROM user' ;   try {   connection . query ( q , ( err , result ) => {     if ( err ) throw err ;     let count = result [ 0 ][ 'COUNT(*)' ];     console . log ( count );     res . render ( "home.ejs" ,{ count });   }); } catch ( err ) {   console . log ( err );   res . send ( "error occured" ); } }); app . listen ( port , () => {   console . log ( `listening to port ${ port } ` ); }); HOME.EJS <! DOCTYPE html > < html lang = "en" > < head >     < meta charset = "UTF-8" >     < meta name = "viewport" content = "width=device-width, initial-scale=1.0" >     < title > home </ title > </ head > < body >     < h2 > Total count of users: <%= count %> </ h2 > </ body > </ html >
Read more

Query Strings

Image
 req.query() - used to get the query string(searched) app . get ( "/search" ,( req , res ) => {   let { q } = req . query ;   // console.log(q);   if ( ! q ){     res . send ( "<h1>nothing searched</h1>" );   }   res . send ( `<h1>search results for ${ q } </h1>` ); });
Read more