大约有 5,880 项符合查询结果（耗时：0.0410秒） [XML]
SQL standard to escape column names?
...ing to SQLite,
'foo' is an SQL string
"foo" is an SQL identifier (column/table/etc)
[foo] is an identifier in MS SQL
`foo` is an identifier in MySQL
For qualified names, the syntax is: "t"."foo" or [t].[foo], etc.
MySQL supports the standard "foo" when the ANSI_QUOTES option is enabled.
...
Count number of rows within each group
...
An old question without a data.table solution. So here goes...
Using .N
library(data.table)
DT <- data.table(df)
DT[, .N, by = list(year, month)]
share
|
...
In JavaScript, why is “0” equal to false, but when tested by 'if' it is not false by itself?
...
Tables displaying the issue:
and ==
Moral of the story use ===
table generation credit: https://github.com/dorey/JavaScript-Equality-Table
sha...
Django - How to rename a model field using South?
...foo', 'full_name', 'name')
The first argument of db.rename_column is the table name, so it's important to remember how Django creates table names:
Django automatically derives the name of the database table from the name of your model class and the app that contains it. A model's database tabl...
How can I define a composite primary key in SQL?
...
Just for clarification: a table can have at most one primary key. A primary key consists of one or more columns (from that table). If a primary key consists of two or more columns it is called a composite primary key. It is defined as follows:
CREATE...
What makes a SQL statement sargable?
...sts. It will literally have to evaluate this function for every row of the table. Much better to use:
WHERE myDate >= '01-01-2008' AND myDate < '01-01-2009'
Some other examples:
Bad: Select ... WHERE isNull(FullName,'Ed Jones') = 'Ed Jones'
Fixed: Select ... WHERE ((FullName = 'Ed Jones') ...
Save PL/pgSQL output from PostgreSQL to a CSV file
...rticular directory, for instance, and the filename might have to have a suitable prefix or extension.
Which tables should the user be able to read/write in the database? This would normally be defined by GRANTs in the database, but the function is now running as a superuser, so tables which would no...
SQL update query using joins
I have to update a field with a value which is returned by a join of 3 tables.
11 Answers
...
Example JavaScript code to parse CSV data
...;
var chars = csv.split(''), c = 0, cc = chars.length, start, end, table = [], row;
while (c < cc) {
table.push(row = []);
while (c < cc && '\r' !== chars[c] && '\n' !== chars[c]) {
start = end = c;
if ('"'...
MySQL Query GROUP BY day / month / year
... Simple complete example: SELECT count(*), record_date FROM anytable WHERE anytable.anycolumn = 'anycondition' GROUP BY YEAR(record_date), month(record_date); note: record_date is a date type TIMESTAMP
– renedet
Jul 25 '17 at 18:35
...