The Sql Join Clause

• Sql Join Clause is used to combine two or more tables.
• To Combine tables we use common columns of tables.
• The Join Clause makes a artificial relation on tables(not realy, effective only at the query)
• We can use where clause instead of join (not for left join, right join,or full join)
• We can use Inner Join instead of join. They are same.

The Join has different types: Left Join, Right Join, Full Join

Syntax for Join Clause

Select columnNames from Table1 join Table2 on Table1.relationColumn= Table2.relationColumn

or with where clause

Select columnNames from Table1, Table2 where Table1.relationColumn= Table2.relationColumn

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The Sql Join Clause Example on Library Database

Sample 1: List all student’s name,surname and the borrow’s taken date.(two tables)

or

Sample 2: List all student’s name,surname,book’s name and the borrow’s taken date.(three table)

or

Note: If we have same column names at different tables,  then we must write the column’s names with their table’s name.

Sample 3: List all student’s name,surname,book’s name,autor name  and the borrow’s taken date.

Select students.name as studentName,students.surname,books.name as BookName,takenDate, authors.name as AuthorName,authors.surname as AuthorSurname from students join borrows on students.studentId = borrows.studentId join books on books.bookId = borrows.bookId join authors on authors.authorId = books.authorId

Sample 4: List all student’s name,surname and the borrow’s taken date, where student name Jefferson.

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