I have a database like this:
+-------------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| PosScore | float | YES | | NULL | |
| NegScore | float | YES | | NULL | |
| SynsetTerms | varchar(45) | YES | | NULL | |
+-------------+-------------+------+-----+---------+----------------+
some of the SynsetTerms have # at the end.
Can I just use an SQL query and remove them?
Thanks in advance.
You can use an update statement:
update t
set SynsetTerms = left(SynsetTerms, length(SynsetTerms) - 1)
where SynsetTerms like '%#';
If you want to remove all occurrences of '#':
update t
set SynsetTerms = replace(SynsetTerms, '#', '')
where SynsetTerms like '%#%';
In your select or update statement just do this:
SELECT replace(synsetTerms, '#','') from table
or
UPDATE table set synsetTerms = replace(synsetTerms, '#','')
if you just want to update the records that contain the '#' symbol you can add the following WHERE clause:
WHERE synsetTerms like '%#'
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 am getting a BadSQLGrammarException, but I cannot see where the error is in the following SQL statement:
insert into comment(comment_date, name, comment) values '4/27/2013', 'Frank', 'Test';
Here is the description of my table. (Yes, I am converting a date into a String. There are probably better ways to do it with SQL, but that's not the question here.)
+--------------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------+--------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| comment_date | varchar(10) | YES | | NULL | |
| name | varchar(200) | YES | | NULL | |
| comment | varchar(200) | YES | | NULL | |
+--------------+--------------+------+-----+---------+-------+
INSERT INTO table (fieldlist) VALUES (valueslist)
^-- ^--
you forgot the indicated brackets.
Try using parentheses around the values, like this:
insert into comment(comment_date, name, comment) values ('4/27/2013', 'Frank', 'Test');
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.
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