I have a self-referencing table, and I am wanting add both the parent and child examples in a single query. Is there a better way to do it then to break it down in a fashion similar to what I have below?
+---------------------+
| example |
+---------+-----------+
| id | parent_id |
+---------+-----------+
| 1 | |
| 2 | 1 |
| 3 | 1 |
| 4 | 1 |
| 5 | |
| 6 | 5 |
| 7 | 5 |
+---------+-----------+
DECLARE example_id INT;
INSERT INTO `example` (parent_id) VALUE("");
SET example_id = LAST_INSERT_ID();
INSERT INTO `example` (parent_id) VALUE (example_id);
If you are referring to tree structure with your question you should better check this article. If you would only have 1 level of children for parent then your way is possibly the simplest way around.
Your way of doing things looks OK.
In a real-world example you'll probably do an insert - select based on some criteria.
INSERT INTO example SELECT
null as id
,e.id as parent_id
,10 as field1
,....
FROM example e WHERE e.somefield = 10 ORDER BY e.id DESC LIMIT 1;
Related
I have a table that looks something like the following:
| id | sub_id | fk_id |
|----|--------|-------|
| 1 | 1 | 1 |
| 2 | 2 | 1 |
| 3 | 3 | 1 |
| 4 | 4 | 1 |
| 5 | 5 | 1 |
| 6 | 1 | 2 |
| 7 | 2 | 2 |
| 8 | 3 | 2 |
| 9 | 4 | 2 |
| 10 | 5 | 2 |
Within this table id is the primary key, and sub_id and fk_id make up a compound unique key, where fk_id is the primary key in another table.
I've found myself in the situation where I need to be able to remove rows within the table, but then renumber sub_id so that there aren't any gaps, e.g. remove (1, 1, 1) and all rows where fk_id=1 have their respective sub_id renumbered as 1, 2, 3, 4, etc.
I also need to be able to remove one or more rows at a time, then trigger the re-numbering (as I assume it's inefficient to try and renumber them multiple times when once will suffice). However, there's a maximum of 60 rows for each value of fk_id but there can be thousands of different values of fk_id.
How should I go about the re-numbering? I'm think some sort of INSERT ... SELECT query, but I can't get my head around how it should work.
You can renumber the rows for a given fk_id using this query:
select t_renum.*, count(t_lower.id) as new_sub_id
from mytable t_renum
join mytable t_lower
on t_lower.fk_id = t_renum.fk_id
and t_lower.id <= t_renum.id
where t_renum.fk_id = #renumber_fk_id
group by t_renum.id
The result can be joined with the original table for update like this:
update mytable t
join (
select t_renum.*, count(t_lower.id) as new_sub_id
from mytable t_renum
join mytable t_lower
on t_lower.fk_id = t_renum.fk_id
and t_lower.id <= t_renum.id
where t_renum.fk_id = #renumber_fk_id
group by t_renum.id
) t_renum using (id)
set t.sub_id = t_renum.new_sub_id
sqlfiddle
After digging around more, I discovered another answer that was remarkably simple and avoided the need for a new table which is recommended in many similar questions. I converted it to a stored procedure which suits my needs better:
DELIMITER //
CREATE PROCEDURE reindex (IN fk_key INT UNSIGNED)
BEGIN
SET #num := 0;
UPDATE example
SET sub_id = (#num := #num + 1)
WHERE fk_id = fk_key
ORDER BY id;
END //
DELIMITER ;
we have a very old custom db (oracle, mysql, derby) with the restrictions: no new table fileds, no views, no functions, no procedures.
My table MYTABLE:
| id | ... | parent_id |
------------------------
| 1 | ... | |
| 2 | ... | 1 |
| 3 | ... | 1 |
| 4 | ... | 2 |
| 5 | ... | 1 |
and I my first statement:
select * from MYTABLE where id in ('1','2','3','4','5');
give my 5 records.
Then I need the information about the first (no deeper) child ids.
My current solution:
for (record in records) {
// get child ids as comma separated string list
// e.g. "2,3,5" for id 1
String childIds = getChildIds(record.id);
}
with the second statement in getChildIds(record.Id):
select id from MYTABLE where parent_id='record.Id';
So I have 1 + 5 = 6 statements for the required information.
I'm looking for a solution to select the records from the following "imaginary" table with the "imaginary" field "child_ids":
| id | ... | parent_id | child_ids |
------------------------------------
| 1 | ... | | 2,3,5 |
| 2 | ... | 1 | 4 |
| 3 | ... | 1 | |
| 4 | ... | 2 | |
| 5 | ... | 1 | |
Does anyone have an idea how I can get this information with only one statement (or with 2 statements)?
Thanks for your help, Thomas
FOR MYSQL:
How about using the GROUP_CONCAT() function like the following:
SELECT id, parent_id,
GROUP_CONCAT(child_id ORDER BY child_id SEPARATOR ',') AS child_ids
FROM MYTABLE
WHERE id IN ('1','2','3','4','5')
FOR ORACLE:
If you have a later version of Oracle you could use the LISTAGG() function:
SELECT parent_id,
LISTAGG(child_id, ', ') WITHIN GROUP (ORDER BY child_id) "child_ids"
FROM MYTABLE
WHERE id IN ('1','2','3','4','5')
GROUP BY parent_id
FOR DERBY:
I don't know anything about derby, but doing a little research it uses IBM DB2 SQL syntax. So, maybe using a combination of XMLSERIALIZE(), XMLAGG(), and XMLTEXT() will work for you:
SELECT parent_id,
XMLSERIALIZE(XMLAGG(XMLTEXT(child_id) ORDER BY child_id) AS CLOB(30K))
FROM table GROUP BY parent_id
I've come across this problem numerous times but haven't found a "MySQL way" to solve the issue as such - I have a database that contains users and reports. Each report has an id which I display as a report number to my users.
The main complaint is that users are confused as to why reports have gone missing from their system. This is not actually the case. It is actually that they are recognizing a gap between their IDs and assume that these are missing reports, when in actual fact, it is simply becasue another user has filled in this auto-incrementing gap.
I need to know if there is a way to do this in MySQL:
Is it possible that I can have a second auto-increment field called report_number which is based on a user_id field which has a different set of auto-increments per user?
e.g.
|------|---------|---------------|
| id | user_id | report_number |
|------|---------|---------------|
| 1 | 1 | 1 |
| 2 | 1 | 2 |
| 3 | 1 | 3 |
| 4 | 2 | 1 |
| 5 | 1 | 4 |
| 6 | 1 | 5 |
| 7 | 2 | 2 |
| 8 | 3 | 1 |
| 9 | 3 | 2 |
|------|---------|---------------|
I am using InnoDB for this as it is quite heavily weighted with foreign-keys. It appears to complain when I add a second auto increment field, but I wasn't sure if there was a different way to do this?
MyISAM supports the second column with auto increment, but InnoDB doesn't.
For InnoDB you might create a trigger BEFORE INSERT to get the max value of the reportid and add one to the value.
DELIMITER $$
CREATE TRIGGER report_trigger
BEFORE INSERT ON reports
FOR EACH ROW BEGIN
SET NEW.`report_id` = (SELECT MAX(report_id) + 1 FROM reports WHERE user_id = NEW.user_id);
END $$
DELIMITER ;
If you can use MyISAM instead, in the documentation of MySQL page there is an example:
http://dev.mysql.com/doc/refman/5.0/en/example-auto-increment.html
CREATE TABLE animals (
grp ENUM('fish','mammal','bird') NOT NULL,
id MEDIUMINT NOT NULL AUTO_INCREMENT,
name CHAR(30) NOT NULL,
PRIMARY KEY (grp,id)
) ENGINE=MyISAM;
INSERT INTO animals (grp,name) VALUES
('mammal','dog'),('mammal','cat'),
('bird','penguin'),('fish','lax'),('mammal','whale'),
('bird','ostrich');
SELECT * FROM animals ORDER BY grp,id;
Which returns:
+--------+----+---------+
| grp | id | name |
+--------+----+---------+
| fish | 1 | lax |
| mammal | 1 | dog |
| mammal | 2 | cat |
| mammal | 3 | whale |
| bird | 1 | penguin |
| bird | 2 | ostrich |
+--------+----+---------+
Right one with IFNULL:
DELIMITER $$
CREATE TRIGGER salons_trigger
BEFORE INSERT ON salon
FOR EACH ROW BEGIN
SET NEW.salon_id = IFNULL((SELECT MAX(salon_id) + 1 FROM salon WHERE owner = NEW.owner), 1);
END $$
DELIMITER ;
I think mysql doesnt support two auto_increment columns. you can create report number using information schema.
select NULL from information_schema.columns
MySQl does not support two auto incremented fields, if you need then create another table, set the other field which you want to be as auto incremented and you must set up a relationship with these two tables.
I have table:
+----+--------+----------+
| id | doc_id | next_req |
+----+--------+----------+
| 1 | 1 | 4 |
| 2 | 1 | 3 |
| 3 | 1 | 0 |
| 4 | 1 | 2 |
+----+--------+----------+
id - auto incerement primary key.
nex_req - represent an order of records. (next_req = id of record)
How can I build a SQL query get records in this order:
+----+--------+----------+
| id | doc_id | next_req |
+----+--------+----------+
| 1 | 1 | 4 |
| 4 | 1 | 2 |
| 2 | 1 | 3 |
| 3 | 1 | 0 |
+----+--------+----------+
Explains:
record1 with id=1 and next_req=4 means: next must be record4 with id=4 and next_req=2
record4 with id=5 and next_req=2 means: next must be record2 with id=2 and next_req=3
record2 with id=2 and next_req=3 means: next must be record3 with id=1 and next_req=0
record3 with id=3 and next_req=0: means that this is a last record
I need to store an order of records in table. It's important fo me.
If you can, change your table format. Rather than naming the next record, mark the records in order so you can use a natural SQL sort:
+----+--------+------+
| id | doc_id | sort |
+----+--------+------+
| 1 | 1 | 1 |
| 4 | 1 | 2 |
| 2 | 1 | 3 |
| 3 | 1 | 4 |
+----+--------+------+
Then you can even cluster-index on doc_id,sort for if you need to for performance issues. And honestly, if you need to re-order rows, it is not any more work than a linked-list like you were working with.
Am able to give you a solution in Oracle,
select id,doc_id,next_req from table2
start with id =
(select id from table2 where rowid=(select min(rowid) from table2))
connect by prior next_req=id
fiddle_demo
I'd suggest to modify your table and add another column OrderNumber, so eventually it would be easy to order by this column.
Though there may be problems with this approach:
1) You have existing table and need to set OrderNumber column values. I guess this part is easy. You can simply set initial zero values and add a CURSOR for example moving through your records and incrementing your order number value.
2) When new row appears in your table, you have to modify your OrderNumber, but here it depends on your particular situation. If you only need to add items to the end of the list then you can set your new value as MAX + 1. In another situation you may try writing TRIGGER on inserting new items and calling similar steps to point 1). This may cause very bad hit on performance, so you have to carefully investigate your architecture and maybe modify this unusual construction.
Previous Related Posts:
MySQL: how to convert to EAV?
MySQL: how to convert to EAV - Part 2?
Given a table:
TABLE: foo
===============================
| id | first_name | last_name |
===============================
| 1 | John | Doe |
| 2 | Jane | Smith |
| 3 | Ronald | McDonald |
-------------------------------
How do I take this table and convert it to these tables (an EAV implementation)?:
TABLE: attribute
===========================
| id | fk_id | attribute |
===========================
| 1 | 100 | first_name |
| 2 | 100 | last_name |
---------------------------
TABLE: value
=========================================
| id | attribute_id | row_id | value |
=========================================
| 1 | 1 | 1 | John |
| 2 | 2 | 1 | Doe |
| 3 | 1 | 2 | Jane |
| 4 | 2 | 2 | Smith |
| 5 | 1 | 3 | Ronald |
| 6 | 2 | 3 | McDonald |
-----------------------------------------
NOTES:
attribute.fk_id will be provided.
value.row_id is used to identify how the values are grouped as records in the original table.
UPDATE: Also, how do I query the EAV tables so that I can make it look like table foo again.
I give +1 to #Phil's solution for populating the EAV table. Insert one attribute at a time.
Here's another solution to reverse an EAV transformation:
SELECT v.row_id AS id,
MAX(IF(a.attribute='first_name',v.value,NULL)) AS first_name,
MAX(IF(a.attribute='last_name',v.value,NULL)) AS last_name
FROM value v INNER JOIN attribute a
ON v.attribute_id = a.id
GROUP BY v.row_id
Except that by using EAV, you've put all your values into a column of VARCHAR(255) or whatever, so you have lost information about the respective data types of the original columns.
There's really no way to do it "dynamically" without hard-coding the attribute names, either as joins as #Phil shows, or as columns as I show. It's essentially the same problem as trying to write dynamic pivot queries.
I have written more about EAV in my presentation Practical Object-Oriented Models in SQL and in my book, SQL Antipatterns Volume 1: Avoiding the Pitfalls of Database Programming.
I think your only hope is if you use the foo table. bar is essentially useless without the ID.
Try something like this (assuming attribute.id is an auto-increment primary key)
INSERT INTO `attribute` (`fk_id`, `attribute`)
VALUES (100, 'first_name');
INSERT INTO `value` (`attribute_id`, `row_id`, `value`)
SELECT LAST_INSERT_ID(), `id`, `first_name`
FROM `foo`;
INSERT INTO `attribute` (`fk_id`, `attribute`)
VALUES (100, 'last_name');
INSERT INTO `value` (`attribute_id`, `row_id`, `value`)
SELECT LAST_INSERT_ID(), `id`, `last_name`
FROM `foo`;
To reconstruct the foo table, try this
SELECT
`fn`.`row_id` AS `id`,
`fn`.`value` AS `first_name`,
`ln`.`value` AS `last_name`
FROM `value` `fn`
INNER JOIN `attribute` `fn_a`
ON `fn`.`attribute_id` = `fn_a`.`id`
AND `fn_a`.`attribute` = 'first_name'
INNER JOIN `value` `ln`
ON `fn`.`row_id` = `ln`.`row_id`
INNER JOIN `attribute` `ln_a`
ON `ln`.`attribute_id` = `ln_a`.`id`
AND `ln_a`.`attribute` = 'last_name'
Ergh, thanks for reminding me why I hate this pattern