If id1 is primary key in table t1. And I want to create new table t2 and use id1 in t1 as foreign key in t2. What should be my query?

Question

If id1 is primary key in table t1 . And I want to create new table t2 and use id1 in t1 as foreign key in t2 . What should be my query? Is this one right?

create table t2(id2 int primary key, id1 int references t1(id1));

Answer 1

1. In the first step create a second table:

   create table t2(id2 int primary key)

2. In next step we add constraint between t1 and t2. Constraint section is only name - you can use your own definition; foreign key is column name to connect with table; references section is indicate table and column to connect by foreign key.

   ALTER TABLE t2 ADD CONSTRAINT fk_id FOREIGN KEY (id2) REFERENCES t1(id1);

Answer 2

please read this documentation for learning more about foreign key constraint https://dev.mysql.com/doc/refman/8.0/en/create-table-foreign-keys.html

for your case is below

create table t1(id1 int primary key);

create table t2(id2 int , CONSTRAINT FK_t1 FOREIGN KEY (id2)
    REFERENCES t1(id1));

https://dev.mysql.com/doc/refman/5.6/en/create-table-foreign-keys.html https://www.w3schools.com/sql/sql_foreignkey.asp

http://sqlfiddle.com/#!9/9c6c03