The task is to fill the table with N rows of random unique data.
I have the next MySQL table structure:
+----------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| username | varchar(20) | NO | UNI | NULL | |
+----------+--------------+------+-----+---------+----------------+
Username field has string type but if the script will insert numbers its OK.
Theres is dirty solution with INSERT IGNORE, that can make 1000 random rows with endless cycle.
INSERT IGNORE INTO table (id,username) VALUES ('', 1 + ceil(rand() * 1000));
Also, I can use ON DUPLICATE KEY structure, but this 2 solutions are not OK.
I want to make the query, that generate unique username which will be unique and will be inserted from the first time.
So, I tell the script to add 1m of rows and it will insert 1m of unique data without any infelicities.
Any ideas? Thanks.
You can use UUID() which will give you a random string which would fit in your field, guaranteed to be unique with slim chance of collisions.
Related
I have 2 tables called applications and filters. The structure of the tables are as follows:
mysql> DESCRIBE applications;
+-----------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+---------------------+------+-----+---------+----------------+
| id | tinyint(3) unsigned | NO | PRI | NULL | auto_increment |
| name | varchar(255) | NO | | NULL | |
| filter_id | int(3) | NO | | NULL | |
+-----------+---------------------+------+-----+---------+----------------+
3 rows in set (0.01 sec)
mysql> DESCRIBE filters;
+----------+----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+----------------+
| id | smallint(5) unsigned | NO | PRI | NULL | auto_increment |
| name | varchar(100) | NO | | NULL | |
| label | varchar(255) | NO | | NULL | |
| link | varchar(255) | NO | | NULL | |
| anchor | varchar(100) | NO | | NULL | |
| group_id | tinyint(3) unsigned | NO | MUL | NULL | |
| comment | varchar(255) | NO | | NULL | |
+----------+----------------------+------+-----+---------+----------------+
7 rows in set (0.02 sec)
What I want to do is select all the records in applications and make a corresponding record in filters (so that filters.name is the same as applications.name). When the record is inserted in filters I want to get the primary key (filters.id) of the newly inserted record - which is an auto increment field - and update applications.filter_id with it. I should clarify that applications.filter_id is a field I've created for this purpose and contains no data at the moment.
I am a PHP developer and have written a script which can do this, but want to know if it's possible with a pure MySQL solution. In pseudo-code the way my script works is as follows:
Select all the records in applications
Do a foreach loop on (1)
Insert a record in filters (filters.name == applications.name)
Store the inserted ID (filters.id) to a variable and then update applications.filter_id with the variable's data.
I'm unaware of how to do the looping (2) and storing the auto increment ID (4) in MySQL.
I have read about Get the new record primary key ID from mysql insert query? so am aware of LAST_INSERT_ID() but not sure how to reference this in some kind of "loop" which goes through each of the applications records.
Please can someone advise if this is possible?
I don't think this is possible to do this with only one request to mysql.
But, i think this is a good use case for mysql triggers.
I think you should write it like this :
CREATE TRIGGER after_insert_create_application_filter AFTER INSERT
ON applications FOR EACH ROW
BEGIN
INSERT INTO filters (name) VALUES (NEW.name);
UPDATE applications SET filter_id = LAST_INSERT_ID() WHERE id = NEW.id;
END
This trigger is not tested but you should understand the way to write it.
If you don't know mysql triggers, you can read this part of the documentation.
This isn't an answer to your question, more a comment on your database design.
First of all, if the name field needs to contain the same information, they should be the same type and size (varchar(255))
Overall though, I think the schema you're using for your tables is wrong. Your description says that each record in applications can only hold one filter_id. If that is the case, there's no point in using two separate tables.
If there is a chance that there will be a many-to-one relationship, link the records via the relevant primary key. If multiple records in application can relate to a single filter, store filters.id in the applications table. If there are multiple filters for a single application, store applications.id in the filters table.
If there is a many-to-many relationship, create another table to store it:
CREATE TABLE `application_filters_mappings` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`application_id` int(10) unsigned NOT NULL,
`filters_id` int(10) unsigned NOT NULL,
PRIMARY KEY (`id`)
);
It may sound similar but,I am working on partitioning on some table...the table looks like
mysql> DESC SHOPS;
+-------------------+-------------+------+-----+-------------------+-----------------------------+
| Field | Type | Null | Key | Default | Extra |
+-------------------+-------------+------+-----+-------------------+-----------------------------+
| SHOP_ID | int(255) | NO | PRI | NULL | |
| SHOP_NAME | varchar(50) | YES | | NULL | |
| SHOP_CREATED_DATE | timestamp | NO | | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
+-------------------+-------------+------+-----+-------------------+-----------------------------+
3 rows in set (0.00 sec)
so i have search feature where people can search only by shop name so table have around 1 million records so i wanted to RANGE partitioning on shop name alphabetically but i cant do since i have primary key shop_id and shop name can be same...and getting error
ERROR 1503 (HY000): A PRIMARY KEY must include all columns in the
table's partitioning function
Solution:
ALTER TABLE SHOPS ADD CONSTRAINT T UNIQUE (SHOP_ID,SHOP_NAME);
And do partitioning ...i cant do this because it does not make sure shop_id is unique(Primary Key)
You can, and you must. Assuming you always let AUTO_INCREMENT do its thing, shop_id will always be unique, and any index starting with shop_id is all you need.
int(255) -- The (255) means nothing. An INT (SIGNED, by default) has a range of -2 billion to +2 billion and occupies 4 bytes, regardless of the (...) after it..
There is probably no performance advantage (or any other advantage) of Partitioning this table. If you think otherwise, please show us a query that you think will benefit.
Please use SHOW CREATE TABLE; it is more descriptive than DESCRIBE.
witch is the auto increment field in a mysql table?
I have a table structure, for example:
table name is my_table and the fields are my_id, my_name, my_blah.. The one of fields is an auto incremented primary key. Witch is it?
How can I get the name of auto increment field on this table with a php code and/or a mysql query?
You can use the MySQL SHOW COLUMNS query to retrieve information about the columns in a table:
mysql> SHOW COLUMNS FROM `test`;
+----------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| col1 | varchar(100) | YES | | NULL | |
| col2 | int(11) | YES | | NULL | |
+----------+--------------+------+-----+---------+----------------+
The extra column will contain auto_increment for the primary key field.
You could try with a
SHOW COLUMNS FROM TableName
See here: http://dev.mysql.com/doc/refman/5.0/en/show-columns.html
Use a MySQL client and issue the query SHOW CREATE TABLE my_table.
It shows you the code one needs to run to create that table. You can see the column names, types (and lengths), other attributes each column may have (they depend on the type). AUTO_INCREMENT is such an attribute.
It also shows you the PK and the indexes of the table.
I have a string in database (mysql) which is like:
{"StateId":73,"CallTime":"\/Date(1336365498912+0500)\/","CallId":"1336365489.14157","Target":"agi://127.0.0.1"}},"Profile":{"$type":"DataWriter.DbProfile, DataWriterObjects","Name":"DataService","Provider":"mssql","ConnectionString":"Data Source=localhost\\mydb; Database=mydb; User Id=sa; Password=admin;"}}
The string is a JSON object which contains multiple fields. The problem is that I have multiple duplicate rows which I want to remove from the database. A row is considered a duplicate if the CallId and StateId is same but the CallTime is different. So first I want to get list of the duplicates (GROUP BY) of those rows which have CallId same and ignore the difference in CallTime. The below record has different CallTime from the first one but same CallId, hence it is considered a duplicate (basically need not to consider CallTime for duplicate)
{"StateId":73,"CallTime":"\/Date(1336365498913+0500)\/","CallId":"1336365489.14157","Target":"agi://127.0.0.1"}},"Profile":{"$type":"DataWriter.DbProfile, DataWriterObjects","Name":"DataService","Provider":"mssql","ConnectionString":"Data Source=localhost\\mydb; Database=mydb; User Id=sa; Password=admin;"}}
So how do I do a GROUP BY? Basically everything in the GROUP BY should be matched ignoring the CallTime value.
The table structure is
mysql> describe Statements;
+------------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+-------------+------+-----+---------+----------------+
| SequenceId | bigint(10) | NO | PRI | NULL | auto_increment |
| Profile | varchar(32) | YES | MUL | NULL | |
| CacheItem | text | NO | | NULL | |
+------------+-------------+------+-----+---------+----------------+
After that I want to delete the duplicates. Anyone help me out?
I think your database is not atomic enough, you may have to split out your JSON string into separate fields
I am new to database, and run into a time issue when querying a table where no field is indicated as primary key.
for example
+-----------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------+----------+------+-----+---------+-------+
| a_id | char(10) | NO | | | |
| media | char(3) | YES | | NULL | |
| label | char(37) | YES | | NULL | |
As you can see, no of the field have any key specification. When I do a query like
"select label from table where a_id=?", the query is extremely slow. Is this caused by the lack of primary key?
thanks,
No, it is caused by lack of indexes. A primary key must contain a unique and non-null value. If you add an index on the column, it may contain duplicates, but your query will still be faster.
If you want the field to be unique, but you don't want it to be a primary key (although you should wonder why), you can even add a unique index. It will force the value to be unique, but it's no primary key.
That can be convenient when you want the table to have an id and a description that should both be unique. Usually you'll make the id the primary key, and the description just unique.