Sql Select Distinct Group By

Mysql Guide sql distinct delete duplicate records How to use distinct keyword in mysql Filter the result list in a select statement Duplicate value If you want to delete duplicate data query data, you can use the distinct keyword to filter duplicate values, the following distinct usage. select distinct column_name from table_name; Let's take a look at a simple example ...

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 ...

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 ...

Hive in the official document of the query language has a very detailed description, please refer to: http://wiki.apache.org/hadoop/Hive/LanguageManual, most of the content of this article is translated from this page, Some of the things that need to be noted during the use process are added. Create tablecreate [EXTERNAL] TABLE [IF not EXISTS] table_name [col_name data_t ...

Using hive, you can write complex MapReduce query logic efficiently and quickly. In some cases, however, the Hive Computing task can become very inefficient or even impossible to get results, because it is unfamiliar with data attributes or if the Hive optimization convention is not followed. A "good" hive program still needs to have a deep understanding of the hive operating mechanism. Some of the most familiar optimization conventions include the need to write large tables on the right side of the join, and try to use UDF instead of transfrom ... Like。 Here are 5 performance and logic ...

Hive is the most widely used SQL on Hadoop tool, and recently many major data companies have introduced new SQL tools such as Impala,tez,spark, based on column or memory hot data, although many people have a view of hive, inefficient, slow query, and many bugs. But Hive is still the most widely used and ubiquitous SQL on Hadoop tool. Taobao survey analysis of the previous report, Taobao 90% of the business run in hive above. The ratio of the storm audio and video ...

First, the importance of the index The index is used to quickly find a column in a particular value of the line. Instead of using an index, MySQL must start with the first record and then read the entire table until it finds the relevant row. The larger the table, the more time it takes. If the table in the query column index, MySQL can quickly reach a location to search the middle of the data file, there is no need to see all the data. Note that if you need to access most of the rows, sequential reads are much faster since we avoid disk searches. If you use Xinhua Dictionary to find "Zhang" the Chinese characters, do not use the directory, then ...