MySQL FAQs
FAQs Categories
Client Server Commands
Database Structure
Table Types or Storage Engines
Indexes
SQL Statements
Table Joins
Funtions and Operators
Tricky Select Queries
Speed Up Queries
Data Back Up
General Questions
Errors
1PLs Company - #1Payday.Loans Agency - Loans online and near me $100-$2500 (Same Day)
Powered by MySQL
 
Home / Tricky Select Queries / Question No: 63

How to retrieve one child row against each parent id?

How to retrieve only one child row against each parent id even when the child table has multiple matching rows. Multiple rows are like below:
department_id    employee_id
1 1
1 2
2 3
2 4
3 5
3 6
4 7
4 8
4 9
4 10

Answer No: 63

For this MySQL provides GROUP BY which also works even when the SELECT does not specify aggregate function. So the GROUP BY can also be used as follow:
SELECT d.dept_id department_id, e.emp_id AS employee_id  
FROM departments d INNER JOIN employees e
ON e.emp_dept_id = d.dept_id GROUP BY d.dept_id

Related MySQL FAQs to the Above FAQ

How-to-do-numeric-sorting-within-a-string-field-in-MySQL How to do numeric sorting within a string field in MySQL?

How-to-take-data-back-up-of-single-table How to take data back up of single table?

How-to-find-duplicate-records-from-a-table-in-MySQL How to find duplicate records from a table in MySQL?

How-to-get-last-top-records-in-asceding-order How to get last top records in asceding order?

How-to-move-table-from-one-to-another-MySQL-database How to move table from one to another MySQL database?

How-to-get-parent-table-child-table-and-grandchild-table-aggregates-in-MySQL How to get parent table child table and grandchild table aggregates in MySQL?

How-to-skip-repeating-values-from-the-query-results How to skip repeating values from the query results?

An-important-trick-to-speed-up-select-query An important trick to speed up select query.

How-to-find-the-books-which-have-authors-with-more-than-one-book-in-the-table How to find the books which have authors with more than one book in the table?

How-to-count-the-number-of-rows-containing-APOSTROPHE-in-MySQL How to count the number of rows containing APOSTROPHE in MySQL?

How-to-compare-data-of-two-tables-of-two-different-databases-in-MySQL How to compare data of two tables of two different databases in MySQL?

How-to-retreive-multiple-records-without-a-reference-table How to retreive multiple records without a reference table?

About FAQs: Recently Added FAQs

About MySQL FAQs: Site Map | Bookmark Us | Recommend this Site to Your Friend | Contact Us

Useful Links: Wikipedia.org | Oracle.com | w3schools.com | www.php.net | Github.com

© 2024  www.mysqlfaqs.net
All rights reserved.