大约有 37,000 项符合查询结果（耗时：0.0373秒） [XML]
Insert Data Into Temp Table with Query
...query that outputs current data, and I would like to insert it into a Temp table, but am having some issues doing so. Would anybody have some insight on how to do this?
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How to select records from last 24 hours using SQL?
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SELECT *
FROM table_name
WHERE table_name.the_date > DATE_SUB(CURDATE(), INTERVAL 1 DAY)
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When should I use a composite index?
For example, I have a homes table:
9 Answers
9
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What are the best practices for using a GUID as a primary key, specifically regarding performance?
I have an application that uses GUID as the Primary Key in almost all tables and I have read that there are issues about performance when using GUID as Primary Key. Honestly, I haven't seen any problem, but I'm about to start a new application and I still want to use the GUIDs as the Primary Keys, b...
Data structure: insert, remove, contains, get random element, all at O(1)
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Consider a data structure composed of a hashtable H and an array A. The hashtable keys are the elements in the data structure, and the values are their positions in the array.
insert(value): append the value to array and let i be its index in A. Set H[value]=i.
remov...
Search for all occurrences of a string in a mysql database [duplicate]
...how to locate all occurrences of a url in a database. I want to search all tables and all fields. But I have no idea where to start or if it's even possible.
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What is SELF JOIN and when would you use it? [duplicate]
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You use a self join when a table references data in itself.
E.g., an Employee table may have a SupervisorID column that points to the employee that is the boss of the current employee.
To query the data and get information for both people in one row,...
Using R to download zipped data file, extract, and import data
...oad.file("http://www.newcl.org/data/zipfiles/a1.zip",temp)
data <- read.table(unz(temp, "a1.dat"))
unlink(temp)
Compressed (.z) or gzipped (.gz) or bzip2ed (.bz2) files are just the file and those you can read directly from a connection. So get the data provider to use that instead :)
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T-SQL split string
...CTION dbo.splitstring ( @stringToSplit VARCHAR(MAX) )
RETURNS
@returnList TABLE ([Name] [nvarchar] (500))
AS
BEGIN
DECLARE @name NVARCHAR(255)
DECLARE @pos INT
WHILE CHARINDEX(',', @stringToSplit) > 0
BEGIN
SELECT @pos = CHARINDEX(',', @stringToSplit)
SELECT @name = SUBSTRING(@strin...
SQL to find the number of distinct values in a column
...aggregate function:
SELECT COUNT(DISTINCT column_name) AS some_alias FROM table_name
This will count only the distinct values for that column.
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