大约有 43,000 项符合查询结果（耗时：0.0250秒） [XML]
How important is the order of columns in indexes?
I've heard that you should put columns that will be the most selective at the beginning of the index declaration. Example:
...
Group query results by month and year in postgresql
...
select to_char(date,'Mon') as mon,
extract(year from date) as yyyy,
sum("Sales") as "Sales"
from yourtable
group by 1,2
At the request of Radu, I will explain that query:
to_char(date,'Mon') as mon, : convert...
SQL - using alias in Group By
... following order:
FROM clause
WHERE clause
GROUP BY clause
HAVING clause
SELECT clause
ORDER BY clause
For most relational database systems, this order explains which names (columns or aliases) are valid because they must have been introduced in a previous step.
So in Oracle and SQL Server, you...
MySQL “NOT IN” query
...
To use IN, you must have a set, use this syntax instead:
SELECT * FROM Table1 WHERE Table1.principal NOT IN (SELECT principal FROM table2)
share
|
improve this answer
|
...
select into in mysql
...
Use the CREATE TABLE SELECT syntax.
http://dev.mysql.com/doc/refman/5.0/en/create-table-select.html
CREATE TABLE new_tbl SELECT * FROM orig_tbl;
share
|
...
jquery get all form elements: input, textarea & select
Is there an easy way (without listing them all separately) in jquery to select all form elements and only form elements.
12...
MySql : Grant read only options?
...ends 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" everything, to "look but...
Counting null and non-null values in a single query
...le and SQL Server (you might be able to get it to work on another RDBMS):
select sum(case when a is null then 1 else 0 end) count_nulls
, count(a) count_not_nulls
from us;
Or:
select count(*) - count(a), count(a) from us;
...
How to add MVC5 to Visual Studio 2013?
...onger has separate project types for different ASP.Net features.
You must select .NET Framework 4.5 (or higher) in order to see the ASP.NET Web Application template (For ASP.NET One).
So just select Visual C# > Web > ASP.NET Web Application, then select the MVC checkbox in the next step.
Not...
Linq Syntax - Selecting multiple columns
...
.Where(x => x.EMAIL == givenInfo || x.USER_NAME == givenInfo)
.Select(x => new { x.EMAIL, x.ID });
AFAIK, the declarative LINQ syntax is converted to a method call chain similar to this when it is compiled.
UPDATE
If you want the entire object, then you just have to omit the call ...