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常用Sql - 爬虫/数据库 - 清泛IT社区，为创新赋能！
本帖最后由 zqp2013 于 2015-3-17 22:06 编辑
mysql：drop table if exists tablename;
不能写成
drop table tablename if exists tablename;
mysql：建立索引Sql
CREATE TABLE tablename (
`ID` &nbs...
Is it correct to use DIV inside FORM?
...l. You can try it yourself at a HTML validator. Besides, it is almost inevitable these days, since the modern pages are build on div's. If it was not allowed, a simple wrapper or placing the form in a container would already make the page invalid.
– Nrzonline
S...
Syntax of for-loop in SQL Server
...teger in their work (iterating from row to row or result to result in temp tables) and may be thrown off if the increment happens at the beginning of the cycle rather than the end.
– CSS
Feb 3 '16 at 15:22
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Set value to NULL in MySQL
...t NULL inside quotes in your update statement. This should work:
UPDATE table SET field = NULL WHERE something = something
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Array to String PHP?
...e a DB is so you can accomplish work like this trivially. You don't need a table to store arrays, you need a table that you can represent as an array.
Example:
id | word
1 | Sports
2 | Festivals
3 | Classes
4 | Other
You would simply select the data from the table with SQL, rather than have ...
UITableViewCell with UITextView height in iOS 7?
How can I calculate the height of an UITableViewCell with an UITextView in it in iOS 7?
12 Answers
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What is SQL injection? [duplicate]
...rameter substitutes only for a single value. You can't use parameters for table or column identifiers, or SQL keywords, or lists of values in an IN() predicate, or other SQL expressions or syntax. Parameters are useful but you need other techniques for other cases.
– Bill Kar...
MySQL: selecting rows where a column is null
...for a certain column, it returns an empty set. However, when I look at the table in phpMyAdmin, it says null for most of the rows.
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MySQL and GROUP_CONCAT() maximum length
...T SESSION group_concat_max_len = 1000000;
select group_concat(column) from table group by column
You can do this even in sharing hosting, but when you use an other session, you need to repeat the SET SESSION command.
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What happens when a computer program runs?
...me systems)
+---------+
| text | program code, this is the actual executable code that is running.
+---------+
This is the general process address space on many common virtual-memory systems. The "hole" is the size of your total memory, minus the space taken up by all the other areas; this gi...