大约有 12,000 项符合查询结果（耗时：0.0232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:
...
Generate GUID in MySQL for existing Data?
...e BEFORE UPDATE on YourTable
FOR EACH ROW
BEGIN
SET new.guid_column := (SELECT UUID());
END
//
Then execute
UPDATE YourTable set guid_column = (SELECT UUID());
And DROP TRIGGER beforeYourTableUpdate;
UPDATE
Another solution that doesn't use triggers, but requires primary key or unique inde...
In C#, why is String a reference type that behaves like a value type?
...
Not only strings are immutable reference types.
Multi-cast delegates too.
That is why it is safe to write
protected void OnMyEventHandler()
{
delegate handler = this.MyEventHandler;
if (null != handler)
{
handler(this, new EventArgs());
}
}
I suppo...
SQL DROP TABLE foreign key constraint
...your table, you could use this SQL (if you're on SQL Server 2005 and up):
SELECT *
FROM sys.foreign_keys
WHERE referenced_object_id = object_id('Student')
and if there are any, with this statement here, you could create SQL statements to actually drop those FK relations:
SELECT
'ALTER TABL...
JOIN queries vs multiple queries
...han several queries? (You run your main query, and then you run many other SELECTs based on the results from your main query)
...
Correct way to use StringBuilder in SQL
...:
StringBuilder sb = new StringBuilder(some_appropriate_size);
sb.append("select id1, ");
sb.append(id2);
sb.append(" from ");
sb.append(table);
return sb.toString();
Note that I've listed some_appropriate_size in the StringBuilder constructor, so that it starts out with enough capacity for the f...
What exactly do “IB” and “UB” mean?
...by the compiler writers. An example of this is the result of a reinterpret_cast. usually, it simply changes the type of a pointer, without modifying the address, but the mapping is actually implementation-defined, so a compiler could map to a completely different address, as long as it documented th...
Combining “LIKE” and “IN” for SQL Server [duplicate]
...
Effectively, the IN statement creates a series of OR statements... so
SELECT * FROM table WHERE column IN (1, 2, 3)
Is effectively
SELECT * FROM table WHERE column = 1 OR column = 2 OR column = 3
And sadly, that is the route you'll have to take with your LIKE statements
SELECT * FROM tabl...
Build an ASCII chart of the most commonly used words in a given text [closed]
...bars only the last line break is required.
DECLARE @ VARCHAR(MAX),@F REAL SELECT @=BulkColumn FROM OPENROWSET(BULK'A',
SINGLE_BLOB)x;WITH N AS(SELECT 1 i,LEFT(@,1)L UNION ALL SELECT i+1,SUBSTRING
(@,i+1,1)FROM N WHERE i<LEN(@))SELECT i,L,i-RANK()OVER(ORDER BY i)R INTO #D
FROM N WHERE L LIKE'[A-Z...
MySQL JOIN the most recent row only?
...
You may want to try the following:
SELECT CONCAT(title, ' ', forename, ' ', surname) AS name
FROM customer c
JOIN (
SELECT MAX(id) max_id, customer_id
FROM customer_data
GROUP BY customer_id
...