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Is an index needed for a primary key in SQLite?
When an integer column is marked as a primary key in an SQLite table, should an index be explicitly created for it as well? SQLite does not appear to automatically create an index for a primary key column, but perhaps it indexes it anyway, given its purpose? (I will be searching on that column all t...
How to do an INNER JOIN on multiple columns
...nds flights either by the city name or the airport code, but the flights table only contains the airport codes so if I want to search by city I have to join on the airports table.
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What's the difference between using INDEX vs KEY in MySQL?
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There's no difference. They are synonyms.
From the CREATE TABLE manual entry:
KEY is normally a synonym for INDEX. The key attribute PRIMARY KEY can
also be specified as just KEY when given in a column definition. This was
implemented for compatibility with other database sy...
how to mysqldump remote db from local machine
...And change:
mysqldump -P 3310 -h localhost -u mysql_user -p database_name table_name
To:
mysqldump -P 3310 -h 127.0.0.1 -u mysql_user -p database_name table_name
(do not use localhost, it's one of these 'special meaning' nonsense that probably connects by socket rather then by port)
edit: we...
Using group by on multiple columns
...one group.
To illustrate using an example, let's say we have the following table, to do with who is attending what subject at a university:
Table: Subject_Selection
+---------+----------+----------+
| Subject | Semester | Attendee |
+---------+----------+----------+
| ITB001 | 1 | John ...
Why is the tag deprecated in HTML?
...nvas. It is only deprecated because of the war against marquees, centers, tables, frame which is purely religious, as they all have a place.
– Dmitry
Jun 5 '16 at 18:23
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Update or Insert (multiple rows and columns) from subquery in PostgreSQL
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For the UPDATE
Use:
UPDATE table1
SET col1 = othertable.col2,
col2 = othertable.col3
FROM othertable
WHERE othertable.col1 = 123;
For the INSERT
Use:
INSERT INTO table1 (col1, col2)
SELECT col1, col2
FROM othertable
You don't ...
Expand div to max width when float:left is set
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The best way is to use a simple 2 cols table instead of wasting time adding tons of CSS not-cross-browser-compatibles tricks
– Marco Demaio
Nov 23 '12 at 10:22
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Nginx缓存解决方案：SRCache - 更多技术 - 清泛网 - 专注C/C++及内核技术
...request_uri_without_args = ngx.re.sub(ngx.var.request_uri, "\\?.*", "")
table.unpack = table.unpack or unpack
for index, rule in ipairs(phoenix["rule"]) do
if type(rule["regex"]) == "string" then
rule["regex"] = {rule["regex"], ""}
end
local regex, options = table.unp...
Opposite of %in%: exclude rows with values specified in a vector
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If you look at the code of %in%
function (x, table) match(x, table, nomatch = 0L) > 0L
then you should be able to write your version of opposite. I use
`%not in%` <- function (x, table) is.na(match(x, table, nomatch=NA_integer_))
Another way is:
function (x,...