大约有 40,000 项符合查询结果（耗时：0.0221秒） [XML]
Two single-column indexes vs one two-column index in MySQL?
... the statement I provided.
Additionally, MySQL can only use one index per SELECT so a covering index would be the best means of optimizing your queries.
share
|
improve this answer
|
...
A better similarity ranking algorithm for variable length strings
...tr2.length-2).collect {|i| str2[i,2]}.reject {
|pair| pair.include? " "}
union = pairs1.size + pairs2.size
intersection = 0
pairs1.each do |p1|
0.upto(pairs2.size-1) do |i|
if p1 == pairs2[i]
intersection += 1
pairs2.slice!(i)
break
end
end
end
(2.0 * inter...
MySQL 'create schema' and 'create database' - Is there any difference
...asn't been allocated to any particular schema, you can do something like:
SELECT *
FROM your_table
which is equivalent to:
SELECT *
FROM dbo.your_table
Now, SQL server allows the creation of different schema, which gives you the possibility of grouping tables that share a similar purpose. That...
Find and Replace text in the entire table using a MySQL query
...his_text";
$replace = "replace_with_this_text";
$loop = mysql_query("
SELECT
concat('UPDATE ',table_schema,'.',table_name, ' SET ',column_name, '=replace(',column_name,', ''{$find}'', ''{$replace}'');') AS s
FROM
information_schema.columns
WHERE
table_schema = '{...
Get current batchfile directory
... Look, I do not need to run stm.sql in D:\Dir1\Dir2\stm.sql. I need mysql.exe -u root -p mysql < %cd%\stm.sql to execute that stm.sql commands.
– Hamed Kamrava
Jun 12 '13 at 11:32
...
How do I check if an index exists on a table field in MySQL?
...
Try:
SELECT * FROM information_schema.statistics
WHERE table_schema = [DATABASE NAME]
AND table_name = [TABLE NAME] AND column_name = [COLUMN NAME]
It will tell you if there is an index of any kind on a certain column wi...
Group by month and year in MySQL
...
I prefer
SELECT
MONTHNAME(t.summaryDateTime) as month, YEAR(t.summaryDateTime) as year
FROM
trading_summary t
GROUP BY EXTRACT(YEAR_MONTH FROM t.summaryDateTime) DESC";
...
Is there a way to view past mysql queries with phpmyadmin?
...
To view the past queries simply run this query in phpMyAdmin.
SELECT * FROM `general_log`
if it is not enabled, run the following two queries before running it.
SET GLOBAL log_output = 'TABLE';
SET GLOBAL general_log = 'ON';
...
Finding duplicate values in MySQL
...
Do a SELECT with a GROUP BY clause. Let's say name is the column you want to find duplicates in:
SELECT name, COUNT(*) c FROM table GROUP BY name HAVING c > 1;
This will return a result with the name value in the first colum...
MySQL - Rows to Columns
...ms that I'll use for the rest of this post. This will be the base table:
select * from history;
+--------+----------+-----------+
| hostid | itemname | itemvalue |
+--------+----------+-----------+
| 1 | A | 10 |
| 1 | B | 3 |
| 2 | A | 9...