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SQL - using alias in Group By
...if a query was executed in the following order:
FROM clause
WHERE clause
GROUP BY clause
HAVING clause
SELECT clause
ORDER BY clause
For most relational database systems, this order explains which names (columns or aliases) are valid because they must have been introduced in a previous step.
So...
MySQL “Group By” and “Order By”
I want to be able to select a bunch of rows from a table of e-mails and group them by the from sender. My query looks like this:
...
Python extract pattern matches
...re from regex. search for the pattern, if found, retrieve the string using group(index). Assuming valid checks are performed:
>>> p = re.compile("name (.*) is valid")
>>> result = p.search(s)
>>> result
<_sre.SRE_Match object at 0x10555e738>
>>> result.group...
Retrieving the last record in each group - MySQL
...QL implementations. With this standard syntax, we can write greatest-n-per-group queries:
WITH ranked_messages AS (
SELECT m.*, ROW_NUMBER() OVER (PARTITION BY name ORDER BY id DESC) AS rn
FROM messages AS m
)
SELECT * FROM ranked_messages WHERE rn = 1;
Below is the original answer I wrote fo...
What's faster, SELECT DISTINCT or GROUP BY in MySQL?
...two are the same, a query optimizer would have to catch the fact that your GROUP BY is not taking advantage of any group members, just their keys. DISTINCT makes this explicit, so you can get away with a slightly dumber optimizer.
When in doubt, test!
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Java Regex Capturing Groups
...ith the type of quantifier. You're using a greedy quantifier in your first group (index 1 - index 0 represents the whole Pattern), which means it'll match as much as it can (and since it's any character, it'll match as many characters as there are in order to fulfill the condition for the next group...
How to select the rows with maximum values in each group with dplyr? [duplicate]
I would like to select a row with maximum value in each group with dplyr.
6 Answers
6
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Can I concatenate multiple MySQL rows into one field?
...
You can use GROUP_CONCAT:
SELECT person_id, GROUP_CONCAT(hobbies SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;
As Ludwig stated in his comment, you can add the DISTINCT operator to avoid duplicates:
SELECT person_id, GROUP_CO...
mongo group query how to keep fields
Everybody.
In mongo group query, the result shows only the key(s) in arguments. How to keep the first document in each group like mysql query group.
for example:
...
How to configure an existing git repo to be shared by a UNIX group
...is point only been writable by me. I want to open it up to some UNIX user group, foo, so that all members of foo can push to it. I'm aware that I can easily set up a new git repo with:
...