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Difference between clustered and nonclustered index [duplicate]
I need to add proper index to my tables and need some help.
6 Answers
6
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There can be only one auto column
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My MySQL says "Incorrect table definition; there can be only one auto column and it must be defined as a key" So when I added primary key as below it started working:
CREATE TABLE book (
id INT AUTO_INCREMENT NOT NULL,
accepted_terms BIT(1) NO...
How does database indexing work? [closed]
... N/2 block accesses (on average), where N is the number of blocks that the table spans. If that field is a non-key field (i.e. doesn’t contain unique entries) then the entire tablespace must be searched at N block accesses.
Whereas with a sorted field, a Binary Search may be used, which has log2 ...
How to get all registered routes in Express?
...('/api/questions', questionsRoute);
I renamed the document.js file in apiTable.js and adapted it like this:
module.exports = function (baseUrl, routes) {
var Table = require('cli-table');
var table = new Table({ head: ["", "Path"] });
console.log('\nAPI for ' + baseUrl);
console....
Add timestamps to an existing table
I need to add timestamps ( created_at & updated_at ) to an existing table. I tried the following code but it didn't work.
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MySql : Grant read only options?
...ns on database.
It depends on how you define "all read."
"Reading" from tables and views is the SELECT privilege. If that's what you mean by "all read" then yes:
GRANT SELECT ON *.* TO 'username'@'host_or_wildcard' IDENTIFIED BY 'password';
However, it sounds like you mean an ability to "see" ...
Can dplyr package be used for conditional mutating?
...for other better ways to handle the problem, here's another way using data.table:
require(data.table) ## 1.9.2+
setDT(df)
df[a %in% c(0,1,3,4) | c == 4, g := 3L]
df[a %in% c(2,5,7) | (a==1 & b==4), g := 2L]
Note the order of conditional statements is reversed to get g correctly. There's no co...
Can hash tables really be O(1)?
It seems to be common knowledge that hash tables can achieve O(1), but that has never made sense to me. Can someone please explain it? Here are two situations that come to mind:
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Does MySQL index foreign key columns automatically?
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Yes, but only on innodb. Innodb is currently the only shipped table format that has foreign keys implemented.
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Is there a combination of “LIKE” and “IN” in SQL?
...an use REGEXP_LIKE (available from Oracle version 10 onwards).
An example table:
SQL> create table mytable (something)
2 as
3 select 'blabla' from dual union all
4 select 'notbla' from dual union all
5 select 'ofooof' from dual union all
6 select 'ofofof' from dual union all
7 ...