大约有 9,000 项符合查询结果（耗时：0.0275秒） [XML]
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...
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...
SQL keys, MUL vs PRI vs UNI
What is the difference between MUL , PRI and UNI in MySQL?
4 Answers
4
...
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...
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...
BLE（二）信道&数据包&协议栈格式 - 创客硬件开发 - 清泛IT社区，...
...播报文发现、连接其它设备，而在连接建立之后，便开始使用数据报文。无论是广播报文还是数据报文，链路层只使用一种数据包格式，它由“前导码”（preamble）、“访问码”（access code）、”有效载荷“和”循环冗余校验“...
SQL Server: What is the difference between CROSS JOIN and FULL OUTER JOIN?
What is the difference between CROSS JOIN and FULL OUTER JOIN in SQL Server?
10 Answers
...
MySQL dump by query
Is it possible to do mysqldump by single SQL query ?
9 Answers
9
...