大约有 44,000 项符合查询结果（耗时：0.0209秒） [XML]
SQL: How to properly check if a record exists
...
It's better to use either of the following:
-- Method 1.
SELECT 1
FROM table_name
WHERE unique_key = value;
-- Method 2.
SELECT COUNT(1)
FROM table_name
WHERE unique_key = value;
The first alternative should give you no result or one result, the second count should be zero or on...
must appear in the GROUP BY clause or be used in an aggregate function
...
Yes, this is a common aggregation problem. Before SQL3 (1999), the selected fields must appear in the GROUP BY clause[*].
To workaround this issue, you must calculate the aggregate in a sub-query and then join it with itself to get the additional columns you'd need to show:
SELECT m.cname...
SQL join: selecting the last records in a one-to-many relationship
... want to get a list of all customers along with their last purchase in one SELECT statement. What is the best practice? Any advice on building indexes?
...
MySQL: Fastest way to count number of rows
...s.
The solution is SQL_CALC_FOUND_ROWS. This is usually used when you are selecting rows but still need to know the total row count (for example, for paging).
When you select data rows, just append the SQL_CALC_FOUND_ROWS keyword after SELECT:
SELECT SQL_CALC_FOUND_ROWS [needed fields or *] FROM t...
Get the Highlighted/Selected text
...
Getting the text the user has selected is relatively simple. There's no benefit to be gained by involving jQuery since you need nothing other than the window and document objects.
function getSelectionText() {
var text = "";
if (window.getSelecti...
How can I select every other line with multiple cursors in Sublime Text?
In Sublime Text 2, is it possible to instantly select every other (or odd/even) line and place multiple cursors on those lines?
...
Sorting dropdown alphabetically in AngularJS
...
Angular has an orderBy filter that can be used like this:
<select ng-model="selected" ng-options="f.name for f in friends | orderBy:'name'"></select>
See this fiddle for an example.
It's worth noting that if track by is being used it needs to appear after the orderBy filt...
Check if value exists in Postgres array
...
Simpler with the ANY construct:
SELECT value_variable = ANY ('{1,2,3}'::int[])
The right operand of ANY (between parentheses) can either be a set (result of a subquery, for instance) or an array. There are several ways to use it:
SQLAlchemy: how to filt...
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...
How to restore to a different database in sql server?
...restore. Kill all running processes by right clicking on each process and selecting "kill process".
Right click on the database you wish to restore, and select Tasks-->Restore-->From Database.
Select the "From Device:" radio button.
Select ... and choose the backup file of the other database ...