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How do SQL EXISTS statements work?
... criteria -- this is why it can be faster than IN. Also be aware that the SELECT clause in an EXISTS is ignored - IE:
SELECT s.*
FROM SUPPLIERS s
WHERE EXISTS (SELECT 1/0
FROM ORDERS o
WHERE o.supplier_id = s.supplier_id)
...should hit a division by zero error...
How to print binary tree diagram?
...
I was trying to replicate the "selected answer" technique. But I think this one of the best answers here. So Robust and concise.
– Vikrant Goel
Apr 27 '15 at 7:29
...
How to generate unique ID with node.js
...
The fastest possible way to create random 32-char string in Node is by using native crypto module:
const crypto = require("crypto");
const id = crypto.randomBytes(16).toString("hex");
console.log(id); // => f9b327e70bbcf42494ccb28b2d98e00e
...
How many bits or bytes are there in a character? [closed]
How many bits or bytes are there per "character"?
2 Answers
2
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COUNT(*) vs. COUNT(1) vs. COUNT(pk): which is better? [duplicate]
...for all your queries that need to count everything, even for joins, use *
SELECT boss.boss_id, COUNT(subordinate.*)
FROM boss
LEFT JOIN subordinate on subordinate.boss_id = boss.boss_id
GROUP BY boss.id
But don't use COUNT(*) for LEFT joins, as that will return 1 even if the subordinate table doe...
How to select a single field for all documents in a MongoDB collection?
...nt such as:
db.student.find({}, {roll:1, _id:0})
The above statement will select all documents in the students collection, and the returned document will return only the roll field (and exclude the _id).
If we don't mention _id:0 the fields returned will be roll and _id. The '_id' field is always d...
cpuid汇编指令 - C/C++ - 清泛网 - 专注C/C++及内核技术
... spaces
cmp al, 0
jz done
disp_char:
mov dl, al
mov ah, 2
int 21h
lodsb
cmp al, 0
jnz disp_char
done:
mov ax, 4c...
Select first row in each GROUP BY group?
As the title suggests, I'd like to select the first row of each set of rows grouped with a GROUP BY .
17 Answers
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How to create a MySQL hierarchical recursive query
... or self-joins.
MySQL 8+
with recursive cte (id, name, parent_id) as (
select id,
name,
parent_id
from products
where parent_id = 19
union all
select p.id,
p.name,
p.parent_id
from products p
inner join cte
...
Yes/No message box using QMessageBox
...lude <QApplication>
#include <QMessageBox>
int main(int argc, char **argv)
{
QApplication app{argc, argv};
while (QMessageBox::question(nullptr,
qApp->translate("my_app", "Test"),
qApp->translate("my_app", "...