Sql Get Max

SQL statement for querying and deleting duplicate records (i) For example, there is a field "name" in Table A, and the "name" value may be the same between different records, and now you need to query between the records in the table, the "name" value has duplicates, and select name, Count (*) from-a group by name has count (*) > 1 as ...

Method 1 delete yourtable where [id] not in (select max ([id]) from yourtable group by (name + value) b on a.id = b.id where b.id ...

SQL take ABC field duplicate record a record of the maximum value of a field, select Max (a), b,c from table name GROUP by B,c file is very simple. About the Max Max () function The Max function returns the maximum value in a column. Null values are not included in the calculation. SQL Max () syntax select MAX (COLUMN_NAME) from table_name Note: Min and Max can also be used for text columns to get word ...

This article describes the SQL name for filtering duplicate records using a having group by and various select in federated queries to implement a variety of different methods. -1, find redundant records in the table, duplicate records are based on a single field (Peopleid) to determine the code as follows select * from arranges where Peopleid in (select Peopleid from&n ...

MySQL optimization is very important. The most common and most needed optimization is limit. 　　The limit of MySQL brings great convenience to paging, but when the amount of data is large, the performance of limit is reduced dramatically. The same is 10 data select * FROM Yanxue8_visit limit 10000,10 and select * from Yanxue8_visit limit 0,10 is not a quantitative level ...

In our development of the efficiency has been a problem, especially for a lot of large data operations, today we ran into a random query data, at first we may think of the simplest order by RAND () to operate but the efficiency is not flattering ah. Recently, because of the need to study the MySQL random extraction implementation method. For example, to randomly extract a record from the TableName table, the general wording is: SELECT * from TableName ORDER by RAND () LIM ...

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select * from table limit [offset,] rows | rows offset The offset clause clause can be used to force a select statement to return the specified number of records. limit Accepts one or two numeric parameters. The parameter must be an integer constant. Given two parameters, the first parameter specifies the offset of the first record row, and the second parameter specifies the maximum number of record rows to return. The offset of the initial record line is 0 (not 1): ...

Mysql limit usage: When we use the query, often to return to the first few or a few lines in the middle of the data, how to do this time? Do not worry, mysql has provided us with such a function. SELECT * FROM table LIMIT [offset,] rows | rows OFFSET & nbs ...

& http: //www.aliyun.com/zixun/aggregation/37954.html "> The ApacheSqoop (SQL-to-Hadoop) project is designed to facilitate efficient big data exchange between RDBMS and Hadoop. Users can access Sqoop's With help, it is easy to import data from relational databases into Hadoop and its related systems (such as HBase and Hive); at the same time ...