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What does it mean by select 1 from table?
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SELECT 1 FROM TABLE_NAME means, "Return 1 from the table". It is pretty unremarkable on its own, so normally it will be used with WHERE and often EXISTS (as @gbn notes, this is not necessarily best practice, it is, however, common enough t...
SQL Inner-join with 3 tables?
I'm trying to join 3 tables in a view; here is the situation:
12 Answers
12
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SQL JOIN vs IN performance?
... faster more often than not.
So if you are only interested in values from table a you can use this query:
SELECT a.*
FROM a
WHERE EXISTS (
SELECT *
FROM b
WHERE b.col = a.col
)
The difference might be huge if col is not indexed, because the db does not have to find al...
How does collections.defaultdict work?
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Neither. 0 is immutable - in CPython all values from -5 to 256 are cached singletons but this is implementation-specific behaviour - in both cases a new instance is "created" each time with int() or list(). That way, d[k].append(v) can work wi...
PHP + MySQL transactions examples
...b_passwd,$db_name); // error-check this
// note: this is meant for InnoDB tables. won't work with MyISAM tables.
try {
$conn->autocommit(FALSE); // i.e., start transaction
// assume that the TABLE groups has an auto_increment id field
$query = "INSERT INTO groups (name) ";
$qu...
SQL Query to concatenate column values from multiple rows in Oracle
...es of the ename column (concatenated with a comma) from the employee_names table in an xml element (with tag E)
extract the text of this
aggregate the xml (concatenate it)
call the resulting column "Result"
share
|...
Are there conventions on how to name resources?
...nge in time. So its completely normal that naming conventions that were suitable in the beginning will not be suitable after 2 years. And it's completely fine. You should not try to predict future. Just choose a convention and follow it. You will find if it is suitable for you and your project. If i...
Dump a mysql database to a plaintext (CSV) backup from the command line
...only convenient for mysql to read. CSV seems more universal (one file per table is fine). But if there are advantages to mysqldump, I'm all ears. Also, I'd like something I can run from the command line (linux). If that's a mysql script, pointers to how to make such a thing would be helpful.
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First-time database design: am I overengineering? [closed]
...ds. Unless you are talking about well over a million records in your main tables you seem to be on track to having a sufficiently mainstream design that performance will not be an issue on reasonable hardware.
That said, and this relates to your question 3, with the start you have you probably s...
How to trim a string in SQL Server before 2017?
...ou add database constraints to prevent bad data in the future e.g.
ALTER TABLE Customer ADD
CONSTRAINT customer_names__whitespace
CHECK (
Names NOT LIKE ' %'
AND Names NOT LIKE '% '
AND Names NOT LIKE '% %'
);
Also consider disallowing...