I'm actually developing a synchronization tool in vb.net, I have two database that have on each table records field GUID, this field help to have the same PK on both database. On each record there is also a field called lastUpdated, this field have a milliseconds value, so prevent two user to update the record in the same time. My question is, how I can compare the records of the same table from different db? For example:
ONLINE_DATABASE
TABLE_1
| ID | GUID | NAME | LASTUPDATED |
| 5 | 054ba092-b476-47ed-810b-32868cc95fb| John | 06-01-2016 17:01:12.472438 |
CLIENT_DATABASE
TABLE_1
| ID | GUID | NAME | LASTUPDATED |
| 9 | 054ba092-b476-47ed-810b-32868cc95fb| Jack | 06-01-2016 18:01:12.472438 |
How you can see I've update the record from client application, so I need to apply the same change to online database. Now I've a thousand records to check in about ten tables. So my question is, how I can made a system that do this? Actually I tough to read each row with a MySqlCommand reader but I also think that this procedure is slow... Suggest?
NOTICE THAT: the table have the same name in both db
Related
I am working to split apart this one large table into smaller tables for easier management via foreign keys, and have come across a dilemma with trying to bring the data back together. I am new to working with this type of data merging so I am a bit lost.
There are 3 tables: one table with a list of product owners, one table with a list of systems they are responsible for, and the original table with all of the data (examples below):
Product Owners Table:
+----+---------------+
| id | product_owner |
+----+---------------+
| 1 | User1 |
+----+---------------+
PRIMARY KEY: id
System Table:
+----+-----------+---------------+
| id | system | product_owner |
+----+-----------+---------------+
| 6 | Server1 | NULL |
+----+-----------+---------------+
FOREIGN KEY: product_owner(id)
Original Table:
+---------+---------------+
| system | product_owner |
+---------+---------------+
| Server1 | User1 |
+---------+---------------+
I want to take the data from the original table and merge it with the new system table, however I don't want to go the route of multiple UPDATE statements to add what needs to be added. What's the best route to approach on this?
After a bunch more poking around and reading additional terminology, I was able to solve my problem by using a mix of join statements in conjunction with update, set and where statements:
update system_table a
join original_table.system b
on a.system = b.system
join product_owner c
on c.product_owner = b.product_owner
set a.product_owner = c.id
where c.product_owner = b.product_owner;
I'm building an app in Laravel and have a design question regarding my MySQL db.
Currently I have a table which defines the skills for all the default characters in my game. Because the traits are pulled from a pool of skills, and have a variable number, one of my tables looks something like this:
+----+--------+---------+-----------+
| ID | CharID | SkillID | SkillScore|
+----+--------+---------+-----------+
| 1 | 1 | 15 | 200 |
| 2 | 1 | 16 | 205 |
| 3 | 1 | 12 | 193 |
| 4 | 2 | 15 | 180 |
+----+--------+---------+-----------+
Note the variable number of rows for any given CharID. With my Base Characters entered, I'm at just over 300 rows.
My issue is storing User's copies of their (customized)characters. I don't think storing 300+ rows per user makes sense. Should I store this data in a JSON Blob in another table? Should I be looking at a NoSQL solution like Mongo? Appreciate the guidance.
NB: The entire app centers around using the character's different skills. Mostly reporting from them, but users will also be able to update their SkillScore (likely a few times a week).
ps. Should I consider breaking each character out into their own table and tracking user's characters that way? Users won't be able to add/remove the skills from characters, only update them.
TIA.
Your pivot table looks good to me.
I'd consider dropping the ID column (unless you need it), and using a composite primary key:
PRIMARY_KEY(CharID, SkillID)
Primary keys are indexed so you will get efficient lookups.
As for your other suggestions, if you store this in a JSON column, you'll lose the ability to perform joins, and will therefore end up executing more queries.
My application stores login information of over 2500 employees in a table named "emp_login".
Now I have to store the activities of every employee on daily basis. For this purpose i have created a separate table for every employee. E.g. emp00001, emp0002... Each table will have about 50 columns.
After digging in alot on stackoverflow I'm kind of confused. Many of the experts say that database having more than 200-300 tables on mysql is considered to be poorly designed.
My question is whether it is good idea to have such a bulk of tables? Is my database poorly designed? Should i choose other database like mssql? Or some alternative idea is there to handle the database of such applications??
Do -not- do it that way. Every employee should be in 1 table and have a primary key index ID ie:
1: Tom
2: Pete
You then assign the actions with a column that references the employees ID number
Action, EmployeeID
You should always group identical entities in a table with index ids and then link properties / actions to those entities by Id. Imagine what you would have to do to search a database that consisted of a different table for every employee. Would defeat the whole point of using SQL.
Event table could look like:
Punchin, 1, 2018/01/01 00:00
That would tell you Tom punched In at 2018/01/01 00:00. This is a very simple example, and you prob wouldn’t wanna structure an event table that way but it should get you on the right track.
This is nothing to do with MySQL but to do with your design which is flawed. You should have one table for all your employees. This contains information unique to the employees such as firstname, lastname and email address.
|ID | "John" | "Smith" | "john.smith#gmail.com" |
|1 | "James" | "Smith" | "james.smith#gmail.com" |
|2 | "jane" | "Jones" | "jane.jones.smith#yahoo.com" |
|3 | "Joanne" | "DiMaggio" | "jdimaggio#outlook.com" |
Note the ID column. Typicially this would be an integer with AUTO_INCREMENT set and you would make it the Primary Key. Then you get a new unique number every time you add a new user.
Now you have separate tables for every piece of RELATED data. E.g. the city they live in or their login time (which I'm guessing you want from the table name).
If it's a one to many relationship (i.e. each user has many login times), you create a single extra table which REFERENCES your first table. This is a DEPENDENT table. Like so:
| UserId | LoginTime |
| 1 | "10:00:04 13-09-2018" |
| 2 | "11:00:00 13-09-2018" |
| 3 | "11:29:07 14-09-2018" |
| 1 | "09:00:00 15-09-2018" |
| 2 | "10:00:00 15-09-2018" |
Now when you query your database you do a JOIN on the UserId field to connect the two tables. If it were only their LAST login time, then you could put it in the user table because it would be a single piece of data. But because they will have many login times, then login times needs to be its own table.
(N.b. I haven't put an ID column on this table but it's a good idea.)
If it's data that ISN'T unique to the each user, i.e. it's a MANY to MANY relationship, such as the city they live in, then you need two tables. One contains the cities and the other is an INTERMEDIARY table that joins the two. So as follows:
(city table)
| ID | City |
| 1 | "London" |
| 2 | "Paris" |
| 3 | "New York" |
(city-user table)
| UserID | CityID |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
Then you would do two JOINS to connect all three tables and get which city each employee lived in. Again, I haven't added an ID field and PRIMARY KEY to the intermediary table because it isn't strictly necessary (you could create a unique composite key which is a different discussion) but it would be a good idea.
That's the basic thing you need to know. Always divide your data up by function. Do NOT divide it up by the data itself (i.e. table per user). The thing you want to look up right now is called "Database Normalization". Stick that into a search engine and read a good overview. It wont take long and will help you enormously.
This question already has answers here:
Return rows in the exact order they were inserted
(4 answers)
Closed 4 years ago.
I don't know whether it is already answered. I hadn't got any answers.In Mysql tables, the rows will be arranged in the order of primary key. For example
+----+--------+
| id | name |
+----+--------+
| 1 | john |
| 2 | Bryan |
| 3 | Princy |
| 5 | Danny |
+----+--------+
If I insert anothe row insert into demo_table values(4,"Michael").The table will be like
+----+---------+
| id | name |
+----+---------+
| 1 | john |
| 2 | Bryan |
| 3 | Princy |
| 4 | Michael |
| 5 | Danny |
+----+---------+
But I need the table to be like
+----+---------+
| id | name |
+----+---------+
| 1 | john |
| 2 | Bryan |
| 3 | Prince |
| 5 | Danny |
| 4 | Michael |
+----+---------+
I want the row to be concatenated to the table i.e.,
The rows of the table should be in the order of insertion.Can anybody suggest me the query to get it.Thank you for any answer in advance.
There is in general no internal order to the records in a MySQL table. The only order which exists is the one you impose at the time you query. You typically impose that order using an ORDER BY clause. But there is a bigger design problem here. If you want to order the records by the time when they were inserted, then you should either add a dedicated column to your table which contains a timestamp, or perhaps make the id column auto increment.
If you want to go with the latter option, here is how you would do that:
ALTER TABLE demo_table MODIFY COLUMN id INT auto_increment;
Then, do your insertions like this:
INSERT INTO demo_table (name) VALUES ('Michael');
The database will choose an id value for the Michael record, and in general it would be greater than any already existing id value. If you need absolute control, then adding a timestamp column might make more sense.
Just add another Column Created (Timestamp) in your table to store the time of insertion
Then use this Command for insertion
insert into demo_table id, name,created values(4,"Michael",NOW())
The NOW() function returns the current date and time.
Since you are recording the timestamp, it can be also used for future reference too
It's not clear why you want to control the "order" in which the data is stored in your table. The relational model does not support this; unless you specify an order by clause, the order in which records are returned is not deterministic.. Even if it looks like data is stored in a particular sequence, the underlying database engine can change its mind at any point in time without breaking the standards or documented behaviours.
The fact you observe a particular order when executing a select query without order by is a side effect. Side effects are usually harmless, right up to the point where the mean feature changes and the side effect's behaviour changes too.
What's more - it's generally a bad idea to rely on the primary key to have "meaning". I assume your id column represents a primary key; you should really not rely on any business meaning in primary keys - this is why most people use surrogate keys. Depending on the keys indicating in which order a record was created is probably harmless, but it still seems like a side effect to me. In this, I don't support #TimBiegeleisen's otherwise excellent answer.
If you care about the order in which records were entered, make this explicit in the schema by adding a timestamp column, and write your select statement to order by that timestamp. This is the least sensitive to bugs or changes in the underlying logic/database engine.
I've got multiple entries in table A and would like to display the number of entries in a coloumn of table B. Is there a way to create a dynamic cell-content displaying the number of entries in a table?
I'm a beginner in MySQL and did not find a way to do it so far.
Example table A:
+----+------+------------+
| id | name | birthday |
+----+------+------------+
| 1 | john | 1976-11-18 |
| 2 | bill | 1983-12-21 |
| 3 | abby | 1991-03-11 |
| 4 | lynn | 1969-08-02 |
| 5 | jake | 1989-07-29 |
+----+------+------------+
What I'd like in table B:
+----+------+----------+
| id | name | numusers |
| 1 | tblA | 5 |
+----+------+----------+
In my actual database there is no incrementing ID so just taking the last value would not work - if this would've been a solution.
If MySQL can't handle this the option would be to create some kind of cronjob on my server reading the number of rows and writing them into that cell. I know how to do this - just checking if there's another way.
I'm not looking for a command to run on the mysql-console. What I'm trying to figure out is if there's some option which dynamically changes the cell's value to what I've described above.
You can create a view that will give you this information. The SQL for this view is inspired by an answer to a similar question:
CREATE VIEW table_counts AS
SELECT table_name, table_rows
FROM information_schema.tables
WHERE table_schema = '{your_db}';
The view will have the cells you speak of. As you can see, it is just a filter on an already existing table, so you might consider that this table information_schema.tables is the answer to your question.
You can do that directly with COUNT() for example SELECT COUNT(*) FROM TblA The you get all rows from that table. If you IDXs are ok then its very fast. If you write it to another table you have to make an request too to get the result of the second table. So i think your can do it directly.
If you have some performance problems there are some other possibilities like Triggers or Stored Procedures to calculate that result and save them in a memory table to get a better performance.