Can a foreign key have duplicate values?
Unlike primary keys, foreign keys can contain duplicate values. Also, it is OK for them to contain NULL values. Though not automatically created for foreign keys, it is a good idea to define them. You can define several foreign key within a table.
What do you understand by foreign keys in a table give a suitable example of foreign keys from a table containing some meaningful data?
Definition: Foreign keys are the columns of a table that points to the primary key of another table. They act as a cross-reference between tables. For example: In the below example the Stu_Id column in Course_enrollment table is a foreign key as it points to the primary key of the Student table.
How to retrieve data from both tables associated with foreign key?
To retrieve data from both table associated with foreign key i.e (common column) you have to join both the tables. if you matching data from both table then use INNER JOIN. > SELECT A.List_Of_columns,B.List_Of_columns FROM Table1 AS A INNER > JOIN Table2 as B ON A.ID=B.ID (Here Id is Common in both table).
Do you need to join two tables with foreign key?
Finally, if you need everything from both tables, matching or not, you can use FULL JOIN. For getting the result from the two table associated with the foreign key, you need to join the tables. You need to join these tables to get the result that you want.
How to get all data from 2 tables?
Using explicit join syntax could help you. Rewrite your query to: SELECT users.email, users.password, data.data_1, data.data_2 FROM users INNER JOIN data ON users.user_id=data.user_id WHERE users.email=’$user_email’ It separates the concerns: conditions that join tables from conditions that restricts the result set. have you tried this? or this?
How to select data from another table in MySQL?
> SELECT A.List_Of_columns,B.List_Of_columns FROM Table1 AS A INNER > JOIN Table2 as B ON A.ID=B.ID (Here Id is Common in both table). If you want matching data from both table along with all records from table1 then use left join instead of Inner Join. if you want all records from table2 use right join.