how to write distinct query in sql

Directory Background Problem Ideas CTE CTE recursive query Conclusion References Background I haven't written a blog for a long time. Recently I encountered a problem: "How can I traverse all the sub-Menus under a parent menu ?" Small and then use the CTE recursive query to solve this problem, sort the records for sharing. Problem How to traverse all sub-Menus under a parent menu? Ideas

', -)Insert intoTb_employeeinfo (Employeeno, EmployeeName, Employeeage)Values(' A1001 ',' LiSi ', +)Insert intoTb_employeeinfo (Employeeno, EmployeeName, Employeeage)Values(' A1002 ',' Wangwu ', +)Insert intoTb_employeeinfo (Employeeno, EmployeeName, Employeeage)Values(' A1003 ',' Zhouliu ', A)Insert intoTb_employeeinfo (Employeeno, EmployeeName, Employeeage)Values(' A1004 ',' Sunqi ', A)Insert intoTb_employeeinfo (Employeeno, EmployeeName, Employeeage)Values(' A1005 ',' Liuba ', at)Insert

data in zipcode of the zip code table. The query statement is used to determine that the zipcode_key variable is not a number, use % to match strings of any length, query all data items containing keywords from the address, city, and province columns in the table, and sort by province, city, and address. This example is relatively simple. As long as you understand the method, you can

If you want to prevent SQL injection, you can only filter the input parameters. For example, you can convert a single quotation mark (') into two single quotation marks (''). however, this approach is not safe. Hackers can bypass single quotes filtering by encoding. to effectively prevent SQL injection, only parameterized query is the final solution. But the prob

same as the result shown in the inner join. Four, two-table relationship is One-to-many, one-to-many or Many-to-many connection statement Of course the above two tables are one-to-one, so if Table A and table B are one-to-many, One-to-many, or many-to-many, how do we write connected SQL statements? In fact, two more than a pair of SQL statements and one-to-on

, resulting in a query failure. Second, the solution: Know the reason, the next analysis and resolution, confirmation is the problem of the code is not uniform. The solution is divided into the following steps: 1, confirm the SQL Server database encoding, my data encoding is GBK. 2, confirm the current PHP script file encoding, my code is UTF-8. 3. Transform the encoding of the

MySQL slow query can help us optimize the efficiency of the MySQL database. The following describes how to enable MySQL slow query to find SQL statements that affect the efficiency. During website operation, the website may suddenly slow down. In general, it is related to the slow MySQL query. You can enable the slow M

How to query slow SQL statements in MySQL 1. query logs (1) enabling MySQL slow query in Windows In Windows, the configuration file of MySQL is usually my. ini. find [mysqld] and add The code is as follows: Log-slow-queries = F:/MySQL/log/mysqlslowquery. LogLong_query_time = 2 (2) enable MySQL slow

is as follows: When the settings are complete, click OK to close. (4) Click on the "Alias" tab on the "Drivers" side and create the new Alias (Aliases-Aliases) like the new driver in step (2), and in the popup window, fill in the Name,username,password, These three items can be filled in arbitrarily, in the Driver option drop-down list to find the Phoenix driver we just added, and then click the "Test" button to test the connection, and then click the "Connect" button, Pop "Connection successf

Solution 5 use xml Parameters If you are not familiar with SQL server xml type parameters, you must first understand the XQuery concept. Here, an XQuery is a language used to search for and extract elements and attributes from XML documents, simply put, the language used to query xml leads to XPath. In fact, XPath is a subset of XQuery. XQuery 1.0 and XPath 2.0 share the same data model, the same functions

Label:Recently doing projects using LINQ in conjunction with EntityFramework to handle database operations. Want to also use for almost a year, found that some use of skills is necessary to pay attention to, special to do under the summary, I hope that the new friends are helpful. At the beginning of the use of the total loop query subquery, the results of poor performance is not good, now look at all feel funny. Also only

all things. Commit: Commit The current thing, there is no need to write things in dynamic SQL, if you want to write please write outside such as: Begin TRAN EXEC (@s) commit trans or write dynamic SQL as a function or stored proc

'); Query in addition to the ' ID ' is not equal to 1 to 3 of the data, then not and between with a space between the previous notlike no space betweenHere is the usage of in: $map[' id '] = array(' in ', ' 1,2,4 '); The query ID is 1,2,4 data; $map[' id '] = array(' not ', ' 1,2,4 '); The query ID is not equal to the data in the one, and there are spaces betwee

reduced.Note: after a temporary table is created, the modification to the primary table is not reflected. Do not lose data when the data in the master table is frequently modified.7. Use sorting to replace non-sequential accessNon-sequential disk access is the slowest operation, as shown in the back-and-forth movement of the disk inventory arm. SQL statements hide this situation, making it easy for us to write