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Mysql joins
This document discusses different types of joins in MySQL, including inner joins, cross joins, left joins, right joins, and self joins. Inner joins return rows when there is a match between both tables based on the join condition. Cross joins return the Cartesian product of the two tables without a join condition. Left joins return all rows from the left table matched or not and return null values for rows that do not match in the right table. Right joins are similar but return all rows from the right table. Self joins allow a table to be joined with itself.
In this document
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Introduction to MySQL joins, their purpose, and types: Inner, Cross, Left, Right, and Self joins.
Explanation of Inner Join, its criteria, and example query demonstrating its use.
Description of Cross Join as a Cartesian join with no conditions, includes example.
Overview of Left Join, which returns all records from the left table and matching ones from the right.
Explanation of Right Join, which retrieves all records from the right table and matching from the left.
Details on Self Join where a table is joined with itself, including a SQL example.
Thank you note, presentation contact information, and invitation for feedback and contact details.
Mysql joins
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- 3. INTRODUCTION Join helpus to retrieve data from multiple tables in a single query. We can use joins in select, update and delete statements. Types of join: 1) Inner join 2) Cross join 3) Left join 4)Right join 5)Self join
- 4. INNER JOIN Thisjoin returns rows when there is at least one match in both the tables. Criteria's before using inner join: 1) first specify the main table it appears in the from clause. 2) Specify the table that want to join with the main table. This is in the inner join clause. 3) Need to specify the join condition or join predicate. The join condition appears after the keyword ON of the INNER JOIN clause. The join condition is the rule for matching rows between the main table and the other tables. Eg: SELECT xx, xxtable.id, yytable.id, yy FROM xxtable INNER JOIN yytable ON xxtable.id=yytable.id;
- 6. SELECT * FROMtable1 t1 INNER JOIN table 2 t2 ON t1.col1=t2.col1
- 7. CROSS JOIN This joinis a Cartesian join that does not necessitate any condition to join. Result set contains record that are multiplication of record number from both the tables. Also known as Cartesian product join Eg: select * from table 1 cross join table 2 ;
- 9. LEFT JOIN LEFTJOIN produces a set of records which matches every entry in the left table regardless of any matching entry in the right table If there is a row in A that matches the WHERE clause, but there is no row in B that matches the ON condition, an extra B row is generated with all columns set to NULL.
- 11. RIGHT JOIN Thisjoin returns all the rows from the right table in conjunction with the matching rows from the left table. If there are no columns matching in the left table, it returns NULL values.
- 12. Example: SELECT * FROMemployee RIGHT OUTER JOIN employee_details ON employee_details.employee_id = employee.employee_id
- 14. SELF JOIN A selfjoin is a join in which a table is joined with itself In this each row of the table is combined with itself and with every other row of the table.
- 15. Example: SELECT e1.name, e2.name,e1.email FROMemployees AS e1, employees AS e2 WHERE e1.email = e2.email
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Editor's Notes
- #11 Table read order forced by left join