+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| pid | varchar(99) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
1 row in set (0.00 sec)
+-------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------------+------+-----+---------+-------+
| pid | varchar(2000) | YES | | NULL | |
| recid | varchar(2000) | YES | | NULL | |
+-------+---------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
This is my table. pid is just the id of the user. "recid" is a recommended song for that user.
I hope to have a list of pid's, and then recommended songs for each person.
Of course, in my 2nd table, (pid, recid) would be unique key.
How do I do a one-to-one query for this ?
# retrieve all songs associated to a given user
SELECT songs.*
FROM user
INNER JOIN songs ON (user.pid = songs.pid)
WHERE user.pid = ?
You may create FKs with query like
ALTER TABLE `foo`
ADD FOREIGN KEY (`bar_id`) REFERENCES `bar` (`id`) ON DELETE RESTRICT ON UPDATE CASCADE
and see the mysql documentation.
Also note that Mysql only supports foreign keys in InnoDB engine.
You want to use a join (inner) to get the information out. Here is a refrence that I've used and have found helpful.
Joins
Related
I have a MySQL database with the following structure :
mysql> describe company;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | int | NO | PRI | NULL | auto_increment |
| name | varchar(50) | NO | | NULL | |
+-------+-------------+------+-----+---------+----------------+
mysql> describe nameserver;
+-----------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+--------------+------+-----+---------+----------------+
| id | int | NO | PRI | NULL | auto_increment |
| companyId | int | NO | MUL | NULL | |
| ns | varchar(250) | NO | MUL | NULL | |
+-----------+--------------+------+-----+---------+----------------+
mysql> describe domain;
+--------------+--------------+------+-----+-------------------+-------------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+--------------+------+-----+-------------------+-------------------+
| id | int | NO | PRI | NULL | auto_increment |
| nameserverId | int | NO | MUL | NULL | |
| domain | varchar(250) | NO | MUL | NULL | |
| tld | varchar(20) | NO | MUL | NULL | |
| createDate | datetime | NO | | CURRENT_TIMESTAMP | DEFAULT_GENERATED |
| updatedAt | datetime | YES | | NULL | |
| status | tinyint | NO | | NULL | |
| fileNo | smallint | NO | MUL | NULL | |
+--------------+--------------+------+-----+-------------------+-------------------+
The indexes structure :
-- Indexes for table `company`
--
ALTER TABLE `company`
ADD PRIMARY KEY (`id`);
--
-- Indexes for table `domain`
--
ALTER TABLE `domain`
ADD PRIMARY KEY (`id`),
ADD KEY `nameserver` (`nameserverId`),
ADD KEY `domain` (`domain`),
ADD KEY `tld` (`tld`),
ADD KEY `fileNo` (`fileNo`);
--
-- Indexes for table `nameserver`
--
ALTER TABLE `nameserver`
ADD PRIMARY KEY (`id`),
ADD KEY `company` (`companyId`),
ADD KEY `ns` (`ns`);
--
-- AUTO_INCREMENT for dumped tables
--
--
-- AUTO_INCREMENT for table `company`
--
ALTER TABLE `company`
MODIFY `id` int NOT NULL AUTO_INCREMENT;
--
-- AUTO_INCREMENT for table `domain`
--
ALTER TABLE `domain`
MODIFY `id` int NOT NULL AUTO_INCREMENT;
--
-- AUTO_INCREMENT for table `nameserver`
--
ALTER TABLE `nameserver`
MODIFY `id` int NOT NULL AUTO_INCREMENT;
--
-- Constraints for dumped tables
--
--
-- Constraints for table `domain`
--
ALTER TABLE `domain`
ADD CONSTRAINT `nameserver` FOREIGN KEY (`nameserverId`) REFERENCES `nameserver` (`id`);
--
-- Constraints for table `nameserver`
--
ALTER TABLE `nameserver`
ADD CONSTRAINT `company` FOREIGN KEY (`companyId`) REFERENCES `company` (`id`);
The amount of data is as following:
domain table about 500 millions records
nameserver table about 2 millions records
Running this query take about 4 hours to get me the result :
SELECT distinct domain FROM domain
INNER join nameserver on nameserver.id = domain.nameserverId
WHERE nameserver.companyId = 2
The explain result for above query :
+----+-------------+------------+------------+------+-------------------
+------------+---------+-----------------------+------+----------+------------------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+------------+------------+------+-------------------+------------+---------+-----------------------+------+----------+------------------------------+
| 1 | SIMPLE | nameserver | NULL | ref | PRIMARY,company | company | 4 | const | 1738 | 100.00 | Using index; Using temporary |
| 1 | SIMPLE | domain | NULL | ref | nameserver,domain | nameserver | 4 | tldzone.nameserver.id | 716 | 100.00 | NULL |
+----+-------------+------------+------------+------+-------------------+------------+---------+-----------------------+------+----------+------------------------------+
My question is how can I improve the speed of getting query from this database?
It is possible for me to change the DB structure or even replace it with another DBMS.
MySQL is running on a VPS with 8.0 GB RAM and dual core CPU.
nameserver: INDEX(companyId, id) -- in this order (you have this)
domain: INDEX(nameserverId, domain) -- in this order
("MUL" does not tell me whether you already have either of these composite indexes. SHOW CREATE TABLE is more descriptive than DESCRIBE.)
1 Add indexes to the relevant columns: Adding indexes to the companyId, nameserverId, and domain columns in the nameserver and domain tables can help to speed up the query by allowing the database to quickly locate the relevant rows.
2 Use a covering index: A covering index is an index that includes all the columns that are used in the query. By creating a covering index on the companyId, nameserverId, and domain columns, you can avoid the need for the database to look up the data in the actual tables, which can improve query performance.
3 Use a column-store index: A column-store index is an index that stores data by column rather than by row. Column-store indexes can be more efficient for querying large datasets and can improve the performance of the query you provided.
4 Use a database management system that is optimized for large datasets: If you are using a database management system that is not well-suited to handling large datasets, you may see improved performance by switching to a different system. Some options to consider include column-oriented database management systems such as Vertica or ClickHouse, or distributed database management systems such as Cassandra or HBase.
5 Consider using a distributed database: If you have a very large dataset and are still experiencing slow query performance, you may want to consider using a distributed database management system, which allows you to spread your data across multiple servers and can improve the scalability and performance of your database.
6 It's important to keep in mind that the specific solutions that work best for you will depend on the specific requirements of your database and the workload you are placing on it. It may be helpful to perform some benchmarking and testing to determine which approaches work best for your needs.
I have a table of this structure:
mysql> desc securities;
+-----------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------------+-------------+------+-----+---------+-------+
| sym | varchar(19) | NO | PRI | | |
| bqn | int(11) | YES | | NULL | |
| sqn | int(11) | YES | | NULL | |
| tqn | int(11) | YES | | NULL | |
+-----------------+-------------+------+-----+---------+-------+
4 rows in set (0.01 sec)
I am trying to do a select and an update within the same query, so the reason I have chosen
insert into securities (sym, bqn, sqn , tqn) values('ANK', 50,0,1577798)
on duplicate key update bqn=bqn+50 , sqn=sqn+0 , tqn=tqn+1577798;
When I ran the above I observed it is in fact changing the values for all the other rows also.
Is this behaviour expected? I am using MySQL Database.
Your fiddle is missing the key, and the INSERT statement in the right panel (where it does not belong in the first place) is using different column names … *sigh*
Define the symbol column as PRIMARY KEY – and use the VALUES() syntax to get the values to add in the ON UPDATE part, so that you don’t have to repeat them every single time:
insert into securities
(symbol, buyerquan, sellerquan , totaltradedquan)
values('BANKBARODA', 73, 0, 4290270)
on duplicate key update
buyerquan=buyerquan+VALUES(buyerquan),
sellerquan=sellerquan+VALUES(sellerquan),
totaltradedquan=totaltradedquan+VALUES(totaltradedquan);
Works perfectly fine, result values are as to be expect from the input: http://sqlfiddle.com/#!2/21638f/1
I have the following table:
mysql> DESC my_contacts;
+----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| id | varchar(20) | NO | PRI | | |
| location | varchar(20) | YES | | NULL | |
| city | varchar(20) | YES | | NULL | |
| state | varchar(2) | YES | | NULL | |
+----------+-------------+------+-----+---------+-------+
4 rows in set (0.01 sec)
If I do a select all I get:
mysql> SELECT * FROM my_contacts;
+----+--------------+------+-------+
| id | location | city | state |
+----+--------------+------+-------+
| 1 | Chester,NJ | NULL | NULL |
| 2 | Katy,TX | NULL | NULL |
| 3 | San Mateo,CA | NULL | NULL |
+----+--------------+------+-------+
3 rows in set (0.00 sec)
I run the following command:
INSERT INTO my_contacts (city,state)
VALUES
(SUBSTRING_INDEX(location,',',1),RIGHT(location,2));
My purpose was to populate the columns city and state with the part before the comma and the part after the comma from the location column.
But the following happened to my table:
mysql> INSERT INTO my_contacts (city,state)
-> VALUES
-> (SUBSTRING_INDEX(location,',',1),RIGHT(location,2));
Query OK, 1 row affected (0.02 sec)
mysql> SELECT * FROM my_contacts;
+----+--------------+------+-------+
| id | location | city | state |
+----+--------------+------+-------+
| | NULL | NULL | NULL |
| 1 | Chester,NJ | NULL | NULL |
| 2 | Katy,TX | NULL | NULL |
| 3 | San Mateo,CA | NULL | NULL |
+----+--------------+------+-------+
4 rows in set (0.00 sec)
I get a record and the id which is the primary key is empty. How is this possible?
I mean it is not NULL but a primary key is not supposed to be empty either right?
You defined your id field as a varchar, which is a dumb idea when you're using it to store integers. an empty field is NOT null. a zero-length string is still a valid string, and therefore a valid id value as far as your table is concerned. Try inserting ANOTHER blank string and you'll get a primary key violation:
INSERT INTO yourtable (id) VALUES (''); // will not work
The id field should be an int type. That'd disallow "empty" values.
primary keys are unique so if you alter the table, then the second row will attempt to add an empty value and fail. as a result, it will attempt the next possible value. If you want the first value not to be empty, you can set a default value.
It's not empty. It's probably an empty string. Note that the datatype is varchar(20).
Well, you didn't assign a value to the primary key field, so the default is NULL.
.
You want to modify the table so the primary key is auto_increment.
You can use a varchar as a foreign key related to another database table, but if you wish to use it as a numerical key, you should utilize a numerical data type such as int.
I know this doesn't answer the precise question regarding the primary key, but as your question does point out the fact you are also having issues parsing out the city and state from your location column, here's the query you would want to use (note you want an UPDATE to modify existing rows, not an INSERT which will add new rows rather than columns):
UPDATE my_contacts
SET
city = substr(location, 1, locate(',', location) - 1),
state = substr(location, locate(',', location) + 1);
I want to add a second foreign key constraint between data and containers. When I delete a container, the data linked to this container has to be deleted too.
The tables:
mysql> DESCRIBE data;
+------------------------+--------------+------+-----+---------------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------------------+--------------+------+-----+---------------------+----------------
| imei | varchar(15) | NO | MUL | NULL |
mysql> DESCRIBE containers;
+--------------------+-------------+------+-----+---------------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------------+-------------+------+-----+---------------------+----------------+
| imei | varchar(15) | NO | MUL | NULL | |
I create a foreign key with this statement:
mysql> ALTER TABLE `data` ADD FOREIGN KEY (`imei`) REFERENCES `containers`(`imei`) ON DELETE CASCADE;
Query OK, 15168 rows affected (0.12 sec)
Records: 15168 Duplicates: 0 Warnings: 0
But the foreign key hasn't been created:
mysql> use INFORMATION_SCHEMA;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Database changed
mysql> select TABLE_NAME,COLUMN_NAME,CONSTRAINT_NAME, REFERENCED_TABLE_NAME,REFERENCED_COLUMN_NAME from KEY_COLUMN_USAGE where REFERENCED_TABLE_NAME = 'containers';
+----------------+-------------+-----------------------+-----------------------+------------------------+
| TABLE_NAME | COLUMN_NAME | CONSTRAINT_NAME | REFERENCED_TABLE_NAME | REFERENCED_COLUMN_NAME |
+----------------+-------------+-----------------------+-----------------------+------------------------+
| container_logs | imei | container_logs_ibfk_1 | containers | imei |
+----------------+-------------+-----------------------+-----------------------+------------------------+
1 row in set (0.16 sec)
What am I doing wrong?
Not all storage engines support foreign keys; storage engines that does not support certain SQL features however do not generate error, but just ignore the statements (actually the SQL parser is higher layer in the MySQL architecture, which uses lower-level APIs to communicate with the storage engines).
So if you are using MyISAM, you cannot create a foreign key, but no error will be returned
I want to be able to insert data into t1 and have data get populated in table t2 with the primary key as a foreign key in t2.
Basically, how come in my current setup when I INSERT INTO t1 (first_name, last_name) values ( "blah", "blah"); and then do SELECT * FROM t2; t2 it says Empty Set (0.00 sec) for t2? Shouldn't it at least show the default id of 1?
t1:
+------------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+------------------+------+-----+---------+----------------+
| first_name | varchar(20) | NO | | NULL | |
| last_name | varchar(20) | NO | | NULL | |
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
+------------+------------------+------+-----+---------+----------------+
t2:
+-----------+------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------+------------------+------+-----+---------+-------+
| address | varchar(50) | NO | | NULL | |
| id | int(10) unsigned | NO | MUL | NULL | |
| last_name | varchar(20) | YES | | NULL | |
+-----------+------------------+------+-----+---------+-------+
In a relational database, a FOREIGN KEY is a declaration that you intend to insert values into T2 that must match an already existing value in T1, and that you want the database to refuse to perform any action that would break this relationship.
It does not mean that the database will create records on its own in order to satisfy a relationship. If you try to insert a value into T2 that does not exist in T1, the command will fail; it will not add the required record to T1.
That is the opposite of what you're suggesting, however, in which you want the foreign key values to get automatically generated. However, there's no requirement that a primary key value actually have references and, furthermore, no limit on the number of times that primary key value can be referenced — so how would the database guess what should be created in T2?
That said, if you want some of your own code to execute automatically when data is added to T1, code which can do whatever you want, you can create a trigger on T1.
No, tables won't propagate automatically. (You can however do it with triggers) You will have to insert into t2.
You can create a trigger on table t1 so that it inserts a row into t2 with the correct id and the other fields NULL
Foreign keys will not insert records for you.
DELIMITER ;;
CREATE TRIGGER insert_addr_rec BEFORE INSERT ON t1
FOR EACH ROW BEGIN
INSERT INTO t2 SET id=NEW.id, last_name=NEW.last_name
END ;;
DELIMITER ;
NB untested code