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Displaying posts with tag: with_recursive (reset)
WITH RECURSIVE and MySQL

If you have been using certain DBMSs, or reading recent versions of the SQL standard, you are probably aware of the so-called “WITH clause” of SQL.
Some call it Subquery Factoring. Others call it Common Table Expression. A form of the WITH CLAUSE, WITH RECURSIVE”, allows to design a recursive query: a query which repeats itself again and again, each time using the results of the previous iteration. This can be quite useful to produce reports based on hierarchical data. And thus is an alternative to Oracle’s CONNECT BY. MySQL does not natively support WITH RECURSIVE, but it is easy to emulate it with a generic, reusable stored procedure. Read the full article …

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WITH RECURSIVE and MySQL

If you have been using certain DBMSs, or reading recent versions of the SQL standard, you are probably aware of the so-called "WITH clause" of SQL.
Some call it Subquery Factoring. Others call it Common Table Expression.
In its simplest form, this feature is a kind of "boosted derived table".

Assume that a table T1 has three columns:


CREATE TABLE T1(
YEAR INT, # 2000, 2001, 2002 ...
MONTH INT, # January, February, ...
SALES INT # how much we sold on that month of that year
);

Now I want to know the sales trend (increase/decrease), year after year:


SELECT D1.YEAR, (CASE WHEN D1.S>D2.S THEN 'INCREASE' ELSE 'DECREASE' END) AS …
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