"expanded_query":"/* select#1 */ select `t_table_1`.`id` AS `id`,`t_table_1`.`task_id` AS `task_id` from `t_table_1` where <in_optimizer>(`t_table_1`.`task_id`,<exists>(/* select#2 */ select `t_table_2`.`id` from `t_table_2` where ((`t_table_2`.`uid` ...
同样保持开关打开,跟踪如下:"steps": [ { "expanded_query": "/* select#2 */ select `t_table_2`.`id` from `t_table_2` where (`t_table_2`.`uid` = 1)" }, { "transformation": { "select#": 2, "from": "IN (SELECT)", "to": "semijoin", "chosen": false } }, { "trans...
Flink usesROW_NUMBER()to remove duplicates, just like the way of Top-N query. In theory, deduplication is a special case of Top-N in which the N is one and order by the processing time or event time. The following shows the syntax of the Deduplication statement: SELECT[column_list]FROM...
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The only change in the sub query will be that we need to use min(CustomerID) instead of max(CustomerID). So the query will be as follows. With Duplicates as (select distinct a.custid as Customer_ID from customers2 a join customers2 b on a.custid <> b.custid and a.CustName = b...
• Query Parsing负责进行词法和语法分析,把程序从人类高可读的格式(即SQL)转化成机器高可读的格式(AST,抽象语法树)。 词法分析指的是把SQL中的字符序列分解成一个个独立的词法单元——Token(<类型,值>)。语法分析指的是从词法分析器输出的token中识别各类短语,并构造出一颗抽象语法树。而按照构造抽象语法树的方...
Query Optimizer 即通常我们所说的"Physical Optimizer",负责把内部查询表达转化成一个高效的查询计划,指导DBMS如何去取表,如何进行排序,如何Join。如下图所示,一个查询计划可以被认为是一个数据流图,在这个数据流图中,表数据会像在管道中传输一样,从一个查询操作符(operator)传递到另一个查询操作符。
After a while you'll likely become bored of this. So you create a job to remove the duplicates. But this doesn't solve the problem. There will still be times between job runs where the table could have duplicates. A better solution is to stop people entering new copies. You could do ...
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SQL allows duplicates in relations as well as in query results. To force the elimination of duplicates, insert the keyword distinct after select. select distinctdept_namefrominstructor The keywordallspecifies that duplicates should not be removed. ...