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卸载SQL Server2000后不能再次安装的问题解决方法 - 爬虫/数据库 - 清泛IT...
曾经由于磁盘空间的问题，卸载了SQL Server2000，可当再次要把它安装上的时候，却怎么也不行了。无论是安装哪一个版本，永远都是同样的错误提示，说是有一个文件已经挂起，必须重新启动计算机。那okay啦，重新启动，再次安...
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...
INNER JOIN vs LEFT JOIN performance in SQL Server
I've created SQL command that uses INNER JOIN on 9 tables, anyway this command takes a very long time (more than five minutes). So my folk suggested me to change INNER JOIN to LEFT JOIN because the performance of LEFT JOIN is better, despite what I know. After I changed it, the speed of query got si...
What is the reason not to use select *?
...on. A few things off the top of my head ....
If you specify columns in a SQL statement, the SQL execution engine will error if that column is removed from the table and the query is executed.
You can more easily scan code where that column is being used.
You should always write queries to bring ba...
How do I list all tables in a schema in Oracle SQL?
How do i list all tables in a schema in Oracle SQL?
14 Answers
14
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How to find Unused Amazon EC2 Security groups
...rom complete. So I decided to write my own script. I used the AWS CLI, MySQL and some “Bash-foo” to perform the following:
Get a list of all EC2 security groups.
I store the group-id, group-name and description in a tabled called “groups” in a MySQL database called aws_security_groups on...
Difference between database and schema
What's the difference between a Database and a Schema in SQL Server? Both are the containers of tables and data.
5 Answers
...
How to check for Is not Null And Is not Empty string in SQL server?
How can we check in a SQL Server WHERE condition whether the column is not null and not the empty string ( '' )?
7 Answe...
SQL keys, MUL vs PRI vs UNI
What is the difference between MUL , PRI and UNI in MySQL?
4 Answers
4
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PadLeft function in T-SQL
...
SQL Server now supports the FORMAT function starting from version 2012, so:
SELECT FORMAT(id, '0000') FROM TableA
will do the trick.
If your id or column is in a varchar and represents a number you convert first:
SELECT...