Say we retrieve table data from a php code.
1- Without delete and restore particular rows from the table and,
2- Without having a column "hidden" (values are 0 or 1) and using the query SELECT ..... WHERE....AND hidden=0
Is it possible to temporary "hide" some of the rows ?
Or else what is the best way to do it ?
An alternative would be to create a VIEW which does not include the unwanted rows; that might be better if the requirement is of a (semi-)permanent nature. See here for more.
How do you know which rows you want to remove? For example, if you know the id for each of the rows you could append an exclusion to your queries
AND id NOT IN (4,9,28)
You can use WHERE id NOT IN
SELECT * FROM talName WHERE id NOT IN (1, 3)
+----+---------+-----+
| id | name | age |
+----+---------+-----+
| 2 | John | 23 |
| 4 | Mary | 21 |
| 5 | Michael | 26 |
+----+---------+-----+
There is no way to hide without deleting, since the mark for hidden is already done (hidden = 1).
Although the correct way is to alter the first query, since you won't retrieve unwanted data, you can:
Query on the query, adding the 'where hidden=0' part
Filter the data inside the script that handles the table
Add a view on the database that is pre-filtering (where hidden=0)
Filter the data on the client (start as hidden everything and using jquery show what you want (not recommended as a solution though)
Related
I have a list of ids in text format as a comma separated value like so
("12345", "12346", "12347", etc, etc)
I would like to find their existence or non existence from a table say devices table which has a column called device ids (not primary key)
Ideally i would like to get a list which says if each item exists or not.
So far I have tried to get the query of those that exist and I have to manually find the non existing ones.
Is there a for loop I have to run on stored procedures or something like that. Please help.
Table structure
<pre>
| id | device_id | device_name |
+------+-----------------+---------------+
| 71 | 352701060409650 | 57X |
| 13 | 352701060409700 | 582 |
</pre>
You need to create a query with left join to the same table with 'IFNULL' condition. There already has been a post for this topic. Please check this out here.
I have put a lot of effort into my database design, but I think I am
now realizing I made a major mistake.
Background: (Skip to 'Problem' if you don't need background.)
The DB supports a custom CMS layer for a website template. Users of the
template are limited to turning pages on and off, but not creating
their own 'new' pages. Further, many elements are non editable.
Therefore, if a page has a piece of text I want them to be able to edit,
I would have 'manually' assigned a static ID to it:
<h2><%= CMS.getDataItemByID(123456) %></h2>
Note: The scripting language is not relevant to this question, but the design forces
each table to have unique column names. Hence the convention of 'TableNameSingular_id'
for the primary key etc.
The scripting language would do a lookup on these tables to find the string.
mysql> SELECT * FROM CMSData WHERE CMSData_data_id = 123456;
+------------+-----------------+-----------------------------+
| CMSData_id | CMSData_data_id | CMSData_CMSDataType_type_id |
+------------+-----------------+-----------------------------+
| 1 | 123456 | 1 |
+------------+-----------------+-----------------------------+
mysql> SELECT * FROM CMSDataTypes WHERE CMSDataType_type_id = 1;
+----------------+---------------------+-----------------------+------------------------+
| CMSDataType_id | CMSDataType_type_id | CMSDataType_type_name | CMSDataType_table_name |
+----------------+---------------------+-----------------------+------------------------+
| 1 | 1 | String | CMSStrings |
+----------------+---------------------+-----------------------+------------------------+
mysql> SELECT * FROM CMSStrings WHERE CMSString_CMSData_data_id=123456;
+--------------+---------------------------+----------------------------------+
| CMSString_id | CMSString_CMSData_data_id | CMSString_string |
+--------------+--------------------------------------------------------------+
| 1 | 123456 | The answer to the universe is 42.|
+--------------+---------------------------+----------------------------------+
The rendered text would then be:
<h2>The answer to the universe is 42.</h2>
This works great for 'static' elements, such as the example above. I used the exact same
method for other data types such as file specifications, EMail Addresses, Dates, etc.
However, it fails for when I want to allow the User to dynamically generate content.
For example, there is an 'Events' page and they will be dynamically created by the
User by clicking 'Add Event' or 'Delete Event'.
An Event table will use keys to reference other tables with the following data items:
Data Item: Table:
--------------------------------------------------
Date CMSDates
Title CMSStrings (As show above)
Description CMSTexts (MySQL TEXT data type.)
--------------------------------------------------
Problem:
That means, each time an Event is created, I need to create the
following rows in the CMSData table;
+------------+-----------------+-----------------------------+
| CMSData_id | CMSData_data_id | CMSData_CMSDataType_type_id |
+------------+-----------------+-----------------------------+
| x | y | 6 | (Event)
| x+1 | y+1 | 5 | (Date)
| x+2 | y+2 | 1 | (Title)
| x+3 | y+3 | 3 | (Description)
+------------+-----------------+-----------------------------+
But, there is the problem. In MySQL, you can have only 1 AUTO INCREMENT field.
If I query for the highest value of CMSData_data_id and just add 1 to it, there
is a chance there is a race condition, and someone else grabs it first.
How is this issue typically resolved - or avoided in the first place?
Thanks,
Eric
The id should be meaningless, except to be unique. Your design should work no matter if the block of 4 ids is contiguous or not.
Redesign your implementation to add the parts separately, not as a block of 4. Doing so should simplify things overall, and improve your scalability.
What about locking the table before writing into it? This way, when you are inserting a row in the CMSData table, you can get the last id.
Other suggestion would be to not have an incremented id, but a unique generated one, like a guid or so.
Lock Tables
Update: Question refined, I still need help!
I have the following table structure:
table reports:
ID | time | title | (extra columns)
1 | 1364762762 | xxx | ...
Multiple object tables that have the following structure
ID | objectID | time | title | (extra columns)
1 | 1 | 1222222222 | ... | ...
2 | 2 | 1333333333 | ... | ...
3 | 3 | 1444444444 | ... | ...
4 | 1 | 1555555555 | ... | ...
In the object tables, on an object update a new version with the same objectID is inserted, so that the old versions are still available. For example see the entries with objectID = 1
In the reports table, a report is inserted but never updated/edited.
What I want to be able to do is the following:
For each entry in my reports table, I want to be able to query the state of all objects, like they were, when the report was created.
For example lets look at the sample report above with ID 1. At the time it was created (see the time column), the current version of objectID 1 was the entry with ID 1 (entry ID 4 did not exist at that point).
ObjectID 2 also existed with it's current version with entry ID 2.
I am not sure how to achieve this.
I could use a query that selects the object versions by the time column:
SELECT *
FROM (
SELECT *
FROM objects
WHERE time < [reportTime]
ORDER BY time DESC
)
GROUP BY objectID
Lets not talk about the performance of this query, it is just to make clear what I want to do. My problem is the comparison of the time columns. I think this is no good way to make sure that I got the right object versions, because the system time may change "for any reason" and the time column would then have wrong data in it, which would lead to wrong results.
What would be another way to do so?
I thought about not using a time column for this, but instead a GLOBAL incremental value that I know the insertion order across the database tables.
If you are interting new versions of the object, and your problem is the time column(I assume you are using this column to sort which one is newer); I suggest you to use an auto-incremental ID column for the versions. Eventually, even if the time value is not reliable for you, the ID will be.Since it is always increasing. So higher ID, newer version.
i have table have prefixed with bok- and inv-
id | number
1 | bok-1
2 | inv-3
3 | bok-2
4 | inv-2
5 | inv-10
6 | bok-3
How can it sorted the field number prefixed with inv-?
Which in this case the result will be:
id | number
1 | bok-1
2 | inv-1
3 | bok-2
4 | inv-2
5 | inv-3
6 | bok-3
You could just use MySQL's SUBSTRING() function:
ORDER BY CAST(SUBSTRING(number, 5) AS SIGNED)
See it on sqlfiddle.
However, it would probably be better to store the prefix and integer parts in separate columns, if at all possible:
ALTER TABLE mytable
ADD COLUMN prefix ENUM('bok', 'inv'),
ADD COLUMN suffix INT;
UPDATE mytable SET
prefix = LEFT(number, 3),
suffix = SUBSTRING(number, 5);
ALTER TABLE mytable
DROP COLUMN number;
Basically you should redesign your database structure. Unfortunately no other options possible processing this efficiently since the database won't index on those dashes. So separate both in 2 fields is the most common practice. Otherwise you will run table scans on every order by clause.
Edit: In addition to the information from the discussion you had: https://chat.stackoverflow.com/rooms/13241/discussion-between-eggyal-and-gusdecool it is clear that this is a wrong design and the operation you are asking for should not be executed at all.
It would be both impossible to realize it without created a decent structure and to create a solution this way which would be legally ok.
Sorry for the confusing question, I will try to clarify.
I have an SQL database ( that I did not create ) that I would like to write a query for. I know very little about SQL, so it is hard for me to even know what to search for to see if this question has already been asked, so sorry if it has. It should be an easy solution for those in the know.
The query I need is for a search I would like to perform on an existing data management system. I want to return all the documents that a given user has NOT signed-off on, as indicated by rows in a signoffs_table. The data is stored similarly to as follows: (this is actually a simplification of the actual schema and hides several LEFT JOINS and columns)
signoffs_table:
| id | user_id | document_id | signers_list |
The naive solution I had was to do something like the following:
SELECT document_id from signoffs_table WHERE (user_id <> $BobsID) AND signers_list LIKE "%Bob%";
This works if ONLY Bob signs the document. The problem is that if Bob and Mary have signed the document then the table looks like this:
signoffs_table:
-----------------------------------------------
| id | user_id | document_id | signers_list |
-----------------------------------------------
| 1 | 10 | 100 | "Bob,Mary,Jim" |
| 2 | 20 | 100 | "Bob,Mary,Jim" |
-----------------------------------------------
(assume Bob's ID = 10 and mary's ID = 20).
and then when I do the query then I get back document_id 100 (in row #2) because there is a row that Bob should have signed, but did not.
Is what I am trying to do possible with the given database structure? I can provide more details if needed. I am not sure how much details are needed.
I guess this query is what you mean:
SELECT document_id FROM signoffs_table AS t1
WHERE signers_list LIKE "%Bob%"
AND NOT EXISTS (
SELECT 1 FROM signoffs_table AS t2
WHERE (t2.user_id = $BobsID) AND t2.document_id = t1.document_id )
I believe your design is incorrect. You have a many-to-many relationship between documents and signers. You should have a junction table, something like:
ID DocumentID SignerID