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MySQL - UPDATE query based on SELECT Query
...can go here
ANSI SQL syntax:
UPDATE tableA SET validation_check =
(SELECT if(start_DTS > end_DTS, 'VALID', '') AS validation_check
FROM tableA
INNER JOIN tableB ON name_A = name_B
WHERE id_A = tableA.id_A)
Pick whichever one seems most natural to you.
...
How to define “type disjunction” (union types)?
...
Miles Sabin describes a very nice way to get union type in his recent blog post Unboxed union types in Scala via the Curry-Howard isomorphism:
He first defines negation of types as
type ¬[A] = A => Nothing
using De Morgan's law this allows him to define union ty...
add column to mysql table if it does not exist
...rade_database_1_0_to_2_0()
BEGIN
-- rename a table safely
IF NOT EXISTS( (SELECT * FROM information_schema.COLUMNS WHERE TABLE_SCHEMA=DATABASE()
AND TABLE_NAME='my_old_table_name') ) THEN
RENAME TABLE
my_old_table_name TO my_new_table_name,
END IF;
-- add a column safely
IF NO...
MySQL maximum memory usage
...e to know how it is possible to set an upper limit on the amount of memory MySQL uses on a Linux server.
6 Answers
...
Intersection and union of ArrayLists in Java
... Test().intersection(list1, list2));
System.out.println(new Test().union(list1, list2));
}
public <T> List<T> union(List<T> list1, List<T> list2) {
Set<T> set = new HashSet<T>();
set.addAll(list1);
set.addAll(list2);
...
Do htmlspecialchars and mysql_real_escape_string keep my PHP code safe from injection?
...nerable to certain attack vectors.
Imagine the following SQL:
$result = "SELECT fields FROM table WHERE id = ".mysql_real_escape_string($_POST['id']);
You should be able to see that this is vulnerable to exploit.
Imagine the id parameter contained the common attack vector:
1 OR 1=1
There's no...
How to subtract 30 days from the current datetime in mysql?
...
SELECT * FROM table
WHERE exec_datetime BETWEEN DATE_SUB(NOW(), INTERVAL 30 DAY) AND NOW();
http://dev.mysql.com/doc/refman/5.5/en/date-and-time-functions.html#function_date-add
...
How do MySQL indexes work?
...be faster to go through the pages one by one (in a database, this is "poor selectivity").
For a 10-page book, it makes no sense to make an index, as you may end up with a 10-page book prefixed by a 5-page index, which is just silly - just scan the 10 pages and be done with it.
The index also needs t...
python-pandas and databases like mysql
...a_conn = cx_Oracle.connect('your_connection_string')
df_ora = pd.read_sql('select * from user_objects', con=ora_conn)
print 'loaded dataframe from Oracle. # Records: ', len(df_ora)
ora_conn.close()
And here is the equivalent example for MySQLdb:
import MySQLdb
mysql_cn= MySQLdb.connect(host='...
Delete all Duplicate Rows except for One in MySQL? [duplicate]
...te.
INSERT INTO tempTableName(cellId,attributeId,entityRowId,value)
SELECT DISTINCT cellId,attributeId,entityRowId,value
FROM tableName;
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