I have two tables that look like this
Train
+----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| TrainID | varchar(11) | NO | PRI | NULL | |
| Capacity | int(11) | NO | | 50 | |
+----------+-------------+------+-----+---------+-------+
Reservations
+---------------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------------+-------------+------+-----+---------+----------------+
| ReservationID | int(11) | NO | PRI | NULL | auto_increment |
| FirstName | varchar(30) | NO | | NULL | |
| LastName | varchar(30) | NO | | NULL | |
| DDate | date | NO | | NULL | |
| NoSeats | int(2) | NO | | NULL | |
| Route | varchar(11) | NO | | NULL | |
| Train | varchar(11) | NO | | NULL | |
+---------------+-------------+------+-----+---------+----------------+
Currently, I'm trying to create a query that will increment the capacity on a Train if a reservation is cancelled. I know I have to perform a Join, but I'm not sure how to do it in an Update statement. For Example, I know how to get the capacity of a Train with given a certain ReservationID, like so:
select Capacity
from Train
Join Reservations on Train.TrainID = Reservations.Train
where ReservationID = "15";
But I'd like to construct the query that does this -
Increment Train.Capacity by ReservationTable.NoSeats given a ReservationID
If possible, I'd like to know also how to Increment by an arbitrary number of seats. As an aside, I'm planning on deleting the reservation after I perform the increment in a Java transaction. Will the delete effect the transaction?
Thanks for the help!
MySQL supports a multi-table UPDATE syntax, which would look approximately like this:
UPDATE Reservations r JOIN Train t ON (r.Train = t.TrainID)
SET t.Capacity = t.Capacity + r.NoSeats
WHERE r.ReservationID = ?;
You can update the Train table and delete from the Reservations table in the same transaction. As long as you do the update first and then do the delete second, it should work.
Here is another example of an UPDATE statement that contains joins to determine the value that is being updated. In this case, I want to update the transactions.payee_id with the related account payment id, if the payee_id is zero (wasn't assigned).
UPDATE transactions t
JOIN account a ON a.id = t.account_id
JOIN account ap ON ap.id = a.pmt_act_id
SET t.payee_id = a.pmt_act_id
WHERE t.payee_id = 0
Related
I have SQL for example
show tables from mydb;
It shows the list of table
|table1|
|table2|
|table3|
Then,I use sql sentence for each table.
such as "show full columns from table1 ;"
+----------+--------+-----------+------+-----+---------+----------------+---------------------------------+---------+
| Field | Type | Collation | Null | Key | Default | Extra | Privileges | Comment |
+----------+--------+-----------+------+-----+---------+----------------+---------------------------------+---------+
| id | bigint | NULL | NO | PRI | NULL | auto_increment | select,insert,update,references | |
| user_id | bigint | NULL | NO | MUL | NULL | | select,insert,update,references | |
| group_id | int | NULL | NO | MUL | NULL | | select,insert,update,references | |
+----------+--------+-----------+------+-----+---------+----------------+---------------------------------+---------+
So in this case I can use programming language such as .(this is not correct code just showing the flow)
tables = "show tables from mydb;"
for t in tables:
cmd.execute("show full columns from {t} ;")
However is it possible to do this in sql only?
If you are using MySQL you can use the system view - INFORMATION_SCHEMA.
It contains table name and column name (and other details). No loop is require and you can easily filter by other information, too.
SELECT *
FROM INFORMATION_SCHEMA.COLUMNS
If you are using Microsoft SQL Server, you can use the above command
I have these two tables that i need to join
fields_data fields
+------------+-----------+------+ +------+-------------+----------+
| relationid | fieldname | data | | name | displayname | position |
+------------+-----------+------+ +------+-------------+----------+
| 2 | ftp | test | | user | Username | top |
| 2 | other | 1234 | | pass | Password | top |
+------------+-----------+------+ | ftp | FTP | top |
| log | Log | top |
| txt | Text | mid |
+------+-------------+----------+
I want to get all the rows from the "fields" table if they have the position "top" AND if a row has a match on name = fieldname from fields_data it should also show the data. This is my join
SELECT
fd.`data`,
fd.`relationid`,
fd.`fieldname`,
f.`name`,
f.`displayname`
FROM `fields` AS f
LEFT OUTER JOIN `fields_data` AS fd
ON fd.`fieldname` = f.`name`
WHERE f.`position`='top' AND (fd.`relationid`='3' OR fd.`relationid` IS NULL)
My problem is that the above query only gives me this result:
+------+------------+-----------+------+-------------+
| data | relationid | fieldname | name | displayname |
+------+------------+-----------+------+-------------+
| NULL | NULL | NULL | user | Username |
| NULL | NULL | NULL | pass | Password |
| NULL | NULL | NULL | log | Log |
+------+------------+-----------+------+-------------+
The field called "ftp" is missing due to it having a relation to "2".. However i still want to display it as result but like the others with NULL in it. And if the SQL query had "fd.relationid='2'" instead of 3 it would give same result, but with the row containing ftp in name, holding data in the three fields.
I hope you get what i mean.. My english is not the best.. Heres the result i want:
with above query containing fd.`relationid`='3'
+------+------------+-----------+------+-------------+
| data | relationid | fieldname | name | displayname |
+------+------------+-----------+------+-------------+
| NULL | NULL | NULL | user | Username |
| NULL | NULL | NULL | pass | Password |
| NULL | NULL | NULL | ftp | FTP |
| NULL | NULL | NULL | log | Log |
+------+------------+-----------+------+-------------+
with above query containing fd.`relationid`='2'
+------+------------+-----------+------+-------------+
| data | relationid | fieldname | name | displayname |
+------+------------+-----------+------+-------------+
| NULL | NULL | NULL | user | Username |
| NULL | NULL | NULL | pass | Password |
| test | 2 | ftp | ftp | FTP |
| NULL | NULL | NULL | log | Log |
+------+------------+-----------+------+-------------+
You want to move the condition to the on clause:
SELECT fd.`data`, fd.`relationid`, fd.`fieldname`, f.`name`, f.`displayname`
FROM `fields` f LEFT OUTER JOIN
`fields_data` fd
ON fd.`fieldname` = f.`name` AND fd.`relationid` = '3'
WHERE f.`position`='top' ;
It is interesting that the semantics of your query and this query are different -- and you found the exact situation: when there is a match on another value, the where clause form filters out the row. This will still keep everything.
As a note, the following also does what you want:
SELECT fd.`data`, fd.`relationid`, fd.`fieldname`, f.`name`, f.`displayname`
FROM `fields` f LEFT OUTER JOIN
(SELECT fd.*
FROM `fields_data` fd
WHERE fd.`relationid` = '3'
) fd
ON fd.`fieldname` = f.`name`
WHERE f.`position` = 'top' ;
I wouldn't recommend writing the query this way, particularly in MySQL (because the subquery is materialized). However, understanding why your version is different from these versions (and why these are the same) is a big step forward in mastering outer joins.
I'm with a great difficulty in formulate a SQL for a module of notifications when a new user register.
I have a database of Notifications, I set up a notification to be sent. Examples:
Send notification when a man and blue eyes register;
Send notification when a woman register;
Send a notification when a blue-eyed woman, brown and work in the company Foo;
With these rules we can see that there can be several possibilities (so the table columns are optional).
Some details:
The table columns are defined as integers because are FK. I just did not put tables because the structure is unnecessary, since the SQL will only relashionship between User and Notification;
The date field is used to store both the date of registration of the notice of such person. So I can only filter to notify the new register of user;
Table Structure
User:
+------------+----------+------+-----+---------+------------+
| Field | Type | Null | Key | Default | Extra |
+------------+----------+------+-----+---------+------------+
| Id | int(11) | NO | PRI | | auto_incre |
| Gender | int(11) | YES | | | |
| HairColor | int(11) | YES | | | |
| EyeColor | int(11) | YES | | | |
| Company | int(11) | YES | | | |
| Date | datetime | NO | | | |
| ... | | | | | |
+------------+----------+------+-----+---------+------------+
Notification:
+------------+----------+------+-----+---------+------------+
| Field | Type | Null | Key | Default | Extra |
+------------+----------+------+-----+---------+------------+
| Id | int(11) | NO | PRI | | auto_incre |
| Gender | int(11) | YES | | | |
| HairColor | int(11) | YES | | | |
| EyeColor | int(11) | YES | | | |
| Company | int(11) | YES | | | |
| Date | datetime | NO | | | |
+------------+----------+------+-----+---------+------------+
Initial idea
The initial idea I had was doing a select for each possibility and joining via union:
-- Selects new users by gender notification
SELECT *
FROM Notification
inner join User on (
User.Date >= Notification.Date and
Notification.Gender = User.Gender and
Notification.HairColor is null and
Notification.EyeColor is null and
Notification.Company is null
)
union all
-- Selects new users by gender and hair color notification
SELECT *
FROM Notification
inner join User on (
User.Date >= Notification.Date and
Notification.Gender = User.Gender and
Notification.HairColor = User.HairColor and
Notification.EyeColor is null and
Notification.Company is null
)
-- ... and so on, doing a select for each option, resulting in 16 selects (4 columns: gender, hair color, eye color and company)
My question is:
Is there another way I can do this SQL querying all the possibilities of notifications in a more easy?
Following this structure of 4 columns we already have 16 selects. In my real structure will have more columns with something unfeasible to keep it that way.
Is there any other suggestion storage structure of the data for a better way to do this functionality?
SELECT *
FROM Notification
inner join User on (
User.Date >= Notification.Date and
(Notification.Gender is null or Notification.Gender = User.Gender) and
(Notification.HairColor is null or Notification.HairColor = User.HairColor) and
(Notification.EyeColor is null Notification.EyeColor = User.EyeColor) and
(Notification.Company is null or Notification.Company = User.Company)
)
This way you get every set of user with the notification stored in the tables.
This is the way I would implement this user registration / notification functionality:
Three tables: Users, Notif_type, Notif_queue.
A trigger on insert on table Users which calls a stored procedure SendNotification(user_id).
The stored proc will have the logic which you can change overtime without having to modify the schema/data. The logic will be:
to select the type of notification (form Notif_type) the new user should receive based on your rules;
to insert a row in Notif_queue which holds a FK to user_id and notif_type_id, so that the functionality notifying the user is completely de-coupled from the notification rules.
why can't you just use the one table "user" and put an extra field/flag called [Notified] so that every time you want to send notifications just refer it to the flag.
i find it irrelevant to use the notification table.
I am trying to build a new table such that the values in the existing table are NOT contained (but obviously the following checks for contained) in another table. Following is my table structure:
mysql> explain t1;
+-----------+---------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------+---------------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| point | bigint(20) unsigned | NO | MUL | 0 | |
+-----------+---------------------+------+-----+---------+-------+
mysql> explain whitelist;
+-------------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+---------------------+------+-----+---------+----------------+
| id | bigint(20) unsigned | NO | PRI | NULL | auto_increment |
| x | bigint(20) unsigned | YES | | NULL | |
| y | bigint(20) unsigned | YES | | NULL | |
| geonetwork | linestring | NO | MUL | NULL | |
+-------------+---------------------+------+-----+---------+----------------+
My query looks like this:
SELECT point
FROM t1
WHERE EXISTS(SELECT source
FROM whitelist
WHERE MBRContains(geonetwork, GeomFromText(CONCAT('POINT(', t1.point, ' 0)'))));
Explain:
+----+--------------------+--------------------+-------+-------------------+-----------+---------+------+------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------------+--------------------+-------+-------------------+-----------+---------+------+------+--------------------------+
| 1 | PRIMARY | t1 | index | NULL | point | 8 | NULL | 1001 | Using where; Using index |
| 2 | DEPENDENT SUBQUERY | whitelist | ALL | _geonetwork | NULL | NULL | NULL | 3257 | Using where |
+----+--------------------+--------------------+-------+-------------------+-----------+---------+------+------+--------------------------+
The query is taking 6 seconds to execute for 1000 records in t1 which is unacceptable for me. How can I rewrite this query using Joins (or perhaps a faster way if that exists) if I don't have a column to join on? Even a stored procedure is acceptable I guess in the worst case. My goal is to finally create a new table containing entries from t1. Any suggestions?
Unless the query optimizer is failing, a WHERE EXISTS construct should result in the same plan as a join with a GROUP clause. Look at optimizing MBRContains(geonetwork, GeomFromText(CONCAT('POINT(', t1.point, ' 0)')))), that's probably where your query is spending all its time. I don't have a suggestion for that, but here's your query written with a JOIN:
Select t1.point
from t1
join whitelist on MBRContains(whitelist.geonetwork, GeomFromText(CONCAT('POINT(', t1.point, ' 0)'))))
group by t1.point
;
or to get the points in t1 not in whitelist:
Select t1.point
from t1
left join whitelist on MBRContains(whitelist.geonetwork, GeomFromText(CONCAT('POINT(', t1.point, ' 0)'))))
where whitelist.id is null
;
This seems like a case where de-nomalizing t1 might be beneficial. Adding a GeomFrmTxt column with a value of GeomFromText(CONCAT('POINT(', t1.point, ' 0)')) could speed up the query you already have.
I have a table with the following format.
mysql> describe unit_characteristics;
+----------------------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------------------+------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| uut_id | int(10) unsigned | NO | PRI | NULL | |
| uut_sn | varchar(45) | NO | | NULL | |
| characteristic_name | varchar(80) | NO | PRI | NULL | |
| characteristic_value | text | NO | | NULL | |
| creation_time | datetime | NO | | NULL | |
| last_modified_time | datetime | NO | | NULL | |
+----------------------+------------------+------+-----+---------+----------------+
each uut_sn has multiple characteristic_name/value pairs. I want to use MySQL to generate a table
+----------------------+-------------+-------------+-------------+--------------+
| uut_sn | char_name_1 | char_name_2 | char_name_3 | char_name_4 | ... |
+----------------------+-------------+-------------+-------------+--------------+
| 00000 | char_val_1 | char_val_2 | char_val_3 | char_val_4 | ... |
| 00001 | char_val_1 | char_val_2 | char_val_3 | char_val_4 | ... |
| 00002 | char_val_1 | char_val_2 | char_val_3 | char_val_4 | ... |
| ..... | char_val_1 | char_val_2 | char_val_3 | char_val_4 | ... |
+----------------------+------------------+------+-----+---------+--------------+
Is this possible with just one query?
Thanks,
-peter
This is a standard pivot query:
SELECT uc.uut_sn,
MAX(CASE
WHEN uc.characteristic_name = 'char_name_1' THEN uc.characteristic_value
ELSE NULL
END) AS char_name_1,
MAX(CASE
WHEN uc.characteristic_name = 'char_name_2' THEN uc.characteristic_value
ELSE NULL
END) AS char_name_2,
MAX(CASE
WHEN uc.characteristic_name = 'char_name_3' THEN uc.characteristic_value
ELSE NULL
END) AS char_name_3,
FROM unit_characteristics uc
GROUP BY uc.uut_sn
To make it dynamic, you need to use MySQL's dynamic SQL syntax called Prepared Statements. It requires two queries - the first gets a list of the characteristic_name values, so you can concatenate the appropriate string into the CASE expressions like you see in my example as the ultimate query.
You're using the EAV antipattern. There's no way to automatically generate the pivot table you describe, without hardcoding the characteristics you want to include. As #OMG Ponies mentions, you need to use dynamic SQL to general the query in a custom fashion for the set of characteristics you want to include in the result.
Instead, I recommend you fetch the characteristics one per row, as they are stored in the database, and if you want an application object to represent a single UUT with all its characteristics, you write code to loop over the rows as you fetch them in your application, collecting them into objects.
For example in PHP:
$sql = "SELECT uut_sn, characteristic_name, characteristic_value
FROM unit_characteristics";
$stmt = $pdo->query($sql);
$objects = array();
while ($row = $stmt->fetch()) {
if (!isset($objects[ $row["uut_sn"] ])) {
$object[ $row["uut_sn"] ] = new Uut();
}
$objects[ $row["uut_sn"] ]->$row["characteristic_name"]
= $row["characterstic_value"];
}
This has a few advantages over the solution of hardcoding characteristic names in your query:
This solution takes only one SQL query instead of two.
No complex code is needed to build your dynamic SQL query.
If you forget one of the characteristics, this solution automatically finds it anyway.
GROUP BY in MySQL is often slow, and this avoids the GROUP BY.