December 27 notes

Connections are divided into internal connections, external connections, and full connections.

External connections include left outer connections and right connections.

Internal connections are also called natural connections.

Select * cannot be written in the brackets of createquery *.

MySQL does not support full join.

 

Inner join: returns only rows with the same link fields in two tables.

Left join: returns records that include all records in the left table and the link fields in the right table.

Table A left join table B left join is based on table A, all data in Table A, some combinations in Table B, and none are null.

Right join: returns all records in the right table that are equal to the link fields in the left table.

Table A right join table B right join is based on table B, all data in Table B, some combinations in Table A, and none are null.

 

 

Select C. *, O. * from customers C, orders owhere C. ID = O. CID full join

 

Select C. *, O. * from customers C inner joinorders o on C. ID = O. CID equivalent inner join

 

Select C. *, O. * from customers C left joinorders o on C. ID = O. CID left Outer Join

 

// Connection Query

// Internal connection

@ Test

Public voidJoin2 (){

Session session = hibernateutil.Getsession();

// Select C. ID, C. realname, O. ID, O. Number fromcustomers as C left join C. Orders as O where c. ID = 1

List <object []> customer =Session. createquery ("select C. ID, C. realname, O. ID, O. number from customersas C left join C. orders as O where c. id = 1 "). list ();

For(Object [] C: customer ){

System.Out. Println (C [0] + "----" + C [1]);

}

}

Result After running:

Hibernate: selectcustomers0 _. ID as col_0_0 _, customers0 _. realname as col_1_0 _, orders1 _. id ascol_2_0 _, orders1 _. number as col_3_0 _ from pros. customers customers0 _ leftouter join pros. orders orders1 _ on customers0 _. id = orders1 _. CID wherecustomers0 _. id = 1

1----435

 

// Criteria method Query

@ Test

Public voidJoin3 (){

Session session = hibernateutil.Getsession();

/* Criteria = session. createcriteria (customers. Class). Add (restrictions. Like ("realname", "% A %"); // The returned criteria object

List <customers> customers = criteria. List ();*/

List <customers> customers =Session. createcriteria (MERS MERs.Class)

. Add (restrictions.Like("Realname", "% A % "))

. Createcriteria ("orders ")

. Add (restrictions.Like("Number", "% 223% "))

. List (); // Chain Query

For(Customers C: customers ){

System.Out. Println (C. getemail ());

}

}

// Scalar Query

@ Test

Public voidJoin4 (){

Session session = hibernateutil.Getsession();

// Session. createsqlquery ("select * from MERs"). List (); array is returned by default.

List <customers> customers =Session. createsqlquery ("select * from MERs"). addentity (customers.Class). List (); // With. addentity (customers. Class) added, the returned object is not an array but an object.

For(Customers C: customers ){

System.Out. Println (C. getemail ());

}

}