Editing Find and remove duplicates (section)

==== Select deduplicated/duplicated records ====
* [http://www.mysqltutorial.org/mysql-distinct.aspx MySQL DISTINCT - Eliminate Duplicate Rows in a Result Set]. Using {{kbd | key =GROUP_CONCAT}} to handle the multiple columns<ref>[http://stackoverflow.com/questions/12188027/mysql-select-distinct-multiple-columns sql - MySQL SELECT DISTINCT multiple columns - Stack Overflow]</ref>
* [http://www.w3schools.com/sql/sql_unique.asp SQL UNIQUE Constraint] "Note that you can have many UNIQUE constraints per table, but only one PRIMARY KEY constraint per table." Quoted from w3schools webpage.
* "{{kbd | key = UNION}} removes duplicates, whereas {{kbd | key = UNION ALL}} does not." source: [http://stackoverflow.com/questions/49925/what-is-the-difference-between-union-and-union-all sql - What is the difference between UNION and UNION ALL? - Stack Overflow]


For counting purpose: find the count of repeated id (type: int) between table_a and table_b
<pre>
SELECT count(DISTINCT(id)) FROM table_a WHERE id IN
(
   SELECT DISTINCT(id) FROM table_b
)
</pre>

Counting number of duplicate occurrence
MySQL: find the number of duplicate occurrence between list_a & list_b which using the same primary key: column name {{kbd | key = id}}
* {{kbd | key = SELECT count(DISTINCT(`id`)) FROM `list_a` WHERE `id` IN (SELECT DISTINCT(`id`) FROM `list_b`) ; }}