ClickHouse是俄罗斯的Yandex于2016年开源的列式存储数据库(DBMS),使用C++语言编写,主要用于在线分析处理查询(OLAP),能够使用SQL查询实时生成分析数据报告。 OLAP(On-Line Analytical Processing)翻译为联机分析处理,专注于分析处理,从对数据库操作来看,OLAP是对数据的查询; OLTP(on-line transactio
pname = sname = "WindowAgg"; break; case T_Unique: pname = sname = "Unique"; break; case T_SetOp: sname = "SetOp"; switch (((SetOp *) plan)->strategy) { case SETOP_SORTED: pname = "SetOp"; strategy = "Sorted"; break; case SETOP_HASHED: pname = "HashSetOp"; strateg...
Result--Run scalar functions that don't involve any table access. --returnReturn rows to the leader or client. Subplan--Used for certain subqueries. UniqueuniqueEliminates duplicates from SELECT DISTINCT and UNION queries. WindowwindowCompute aggregate and ranking window functions. Can operate from ...
import java.util.HashMap; import java.util.Map; import org.apache.flink.api.java.tuple.Tuple2; import org.apache.flink.streaming.api.datastream.DataStream; import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment; import org.apache.flink.table.api.SqlDialect; import org.apache.fl...
hive使用的sql语言我们称为hql。ddl的命令主要有CREATE、ALTER、DROP等。 Hive有一个默认的数据库default,在操作HQL时,如果不明确的指定要使用哪个库,则使用默认数据库; Hive的数据库名、表名均不区分大小写; 名字不能使用数字开头; 不能使用关键字,尽量不使用特殊符号; ...
Referring to the Run SQL Scripts window shown in Figure 1, click on Visual Explain on the toolbar and select Explain to run Visual Explain a second time to see the effect that the newly created index has on query performance. The first thing you should note in the new Visual Explain wind...
How to implement the following analytic (window) functions in MySQL: FIRST_VALUE, LAST_VALUE, LEAD, LAG
In this article, I'll describe several ways to do this in PostgreSQL 8.4. PostgreSQL 8.4 syntax is much richer than that of MySQL. The former can use the analytic functions, recursive CTE's and proprietary syntax extensions, all of which can be used for this task. Let's create a sample...
Since the window specification for both OLAP functions is PARTITION BY rather than ORDER BY, and the outer sub-select doesn't have an ORDER BY clause, strict order on C2 and C3 does not need to be produced by the SORT. Distinct values of C2 just need to be processed by the same data...
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