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mongo group query how to keep fields
...t suggestions]
I came here looking for an answer but wasn't happy with the selected answer (especially given it's age). I found this answer that is a better solution (adapted):
db.test.aggregate({
$group: {
_id: '$name',
person: { "$first": "$$ROOT" },
count: { $sum: 1 }
},
{
"$r...
What is this operator in MySQL?
...d <> both give UNKNOWN with NULL on either side of the expression.)
SELECT *
FROM table
WHERE YourColumn IS NOT NULL;
can also negate the null safe equality operator but this is not standard SQL.
SELECT *
FROM table
WHERE NOT (YourColumn <=> NULL);
...
What is the best collation to use for MySQL with PHP? [closed]
...ng utf8_general_ci.
MySQL will not distinguish between some characters in select statements, if the utf8_general_ci collation is used. This can lead to very nasty bugs - especially for example, where usernames are involved. Depending on the implementation that uses the database tables, this problem...
PHP连接MySQL报错：Fatal error: Call to undefined function mysql_connec...
【问题描述】
PHP测试连接MySQL的程序如下：
<?php
$host='localhost';
$user_name='root';
$password='mysql';
$conn=mysql_connect($host,$user_name,$password);
if (!$conn)
{
die('数据库连接失败：'.mysql_error());
}
echo '数据库连接成功！';
if (mysql_clos...
Truncate all tables in a MySQL database in one command?
...
truncate multiple database tables on Mysql instance
SELECT Concat('TRUNCATE TABLE ',table_schema,'.',TABLE_NAME, ';')
FROM INFORMATION_SCHEMA.TABLES where table_schema in ('db1_name','db2_name');
Use Query Result to truncate tables
Note:
may be you will get this ...
Iterate two Lists or Arrays with one ForEach statement in C#
...Zip method msdn.microsoft.com/en-us/library/dd267698.aspx and return resultSelector(first, second) instead of a KVP.
– Martín Coll
Jun 12 '13 at 19:17
...
Get difference between two lists
...the following simple function.
def diff(list1, list2):
c = set(list1).union(set(list2)) # or c = set(list1) | set(list2)
d = set(list1).intersection(set(list2)) # or d = set(list1) & set(list2)
return list(c - d)
or
def diff(list1, list2):
return list(set(list1).symmetric_d...
Get records with max value for each group of grouped SQL results
...
There's a super-simple way to do this in mysql:
select *
from (select * from mytable order by `Group`, age desc, Person) x
group by `Group`
This works because in mysql you're allowed to not aggregate non-group-by columns, in which case mysql just returns the first row. T...
Remove DEFINER clause from MySQL Dumps
I have a MySQL dump of one of my databases. In it, there are DEFINER clauses which look like,
24 Answers
...
Select last row in MySQL
How can I SELECT the last row in a MySQL table?
10 Answers
10
...