exists

in和exists的区别与SQL执行效率分析

由 馋奶兔 提交于 2019-12-10 18:29:43
【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> 本文对in和exists的区别与SQL执行效率进行了全面整理分析…… 最近很多论坛又开始讨论in和exists的区别与SQL执行效率的问题， 本文特整理一些 in和exists的区别与SQL执行效率分析 SQL中in可以分为三类： 　　1、形如select * from t1 where f1 in ('a','b')，应该和以下两种比较效率 　　select * from t1 where f1='a' or f1='b' 　　或者 select * from t1 where f1 ='a' union all select * from t1 f1='b' 　　你可能指的不是这一类，这里不做讨论。 　　2、形如select * from t1 where f1 in (select f1 from t2 where t2.fx='x')， 　　其中子查询的where里的条件不受外层查询的影响，这类查询一般情况下，自动优化会转成exist语句，也就是效率和exist一样。 　　3、形如select * from t1 where f1 in (select f1 from t2 where t2.fx=t1.fx)， 　　其中子查询的where里的条件受外层查询的影响

Drop if exists in netezza

由 无人久伴 提交于 2019-12-10 17:23:15
问题 I need a command to delete a table if that exists in NETEZZA , Something like that: drop table if exists xxx; I have searched and tried many but it didn't work. Can you help me here? 回答1: In netezza you can use this syntax: drop table table_name if exists; 回答2: There is nothing built-in, but you can create a stored proc which uses the catalog views to check if the table exists before attempting to drop it: create or replace procedure maybe_drop(varchar(128)) returns boolean language nzplsql

Oracle JOIN USING + Subquery : ora-00904 string: invalid identifier

由 泄露秘密 提交于 2019-12-10 15:54:31
问题 i m having a little syntax problem in my query (simplified) : select * from table1 t1 inner join table2 t2 using (pk1) inner join table3 t3 using (pk2) where not exists (select1 from table4 t4 where t4.pk1 = t1.pk1) By using the "using" keyword, oracle doesnt allow table identifier in front of the column name (eg : t1.pk1, only pk1 can be used) If i write : select * from table1 t1 inner join table2 t2 using (pk1) inner join table3 t3 using (pk2) where not exists (select1 from table4 t4 where

File exists.If no other git process is currently running,

由 China☆狼群 提交于 2019-12-10 15:48:07
Unable to create 'C:/Users/zc/IdeaProjects/helloWorld-git/.git/index.lock': File exists. If no other git process is currently running, this probably means a git process crashed in this repository earlier. Make sure no other git process is running and remove the file manually to continue. git锁住了，代码Revert不了，只要把 'C:/Users/zc/IdeaProjects/helloWorld-git/.git/index.lock' 这个文件删掉即可 来源： https://www.cnblogs.com/zhangcheng1/p/12016892.html

Trying to delete when not exists is not working. Multiple columns in primary key

由 巧了我就是萌 提交于 2019-12-10 15:09:32
问题 I am currently trying to delete from Table A where a corresponding record is not being used in Table B. Table A has Section, SubSection, Code, Text as fields, where the first three are the Primary Key. Table B has ID, Section, SubSection, Code as fields, where all four are the Primary Key. There are more columns, but they are irrelevant to this question...just wanted to point that out before I get questioned on why all columns are part of the Primary Key for Table B. Pretty much Table A is a

Elastic Search : General and conditional filters

由 半世苍凉 提交于 2019-12-10 09:50:59
问题 I'm using Elastic Search, with query match_all and filtering. In my situation I want to apply a general filter and filters by condition. Here in pseudo: query: match all (works fine) filter range date between d1 and d2 (works fine without bullet 3) filter (apply only if field exists, but how?) etc. See the following code. I want only apply the "groups" filter if the "groups" field exists! The "exists" filter doesn't take effect in that case. "query": { "filtered": { "query": { "match_all": {}

Magento: addAttributeToFilter but ignore for products that don't have this attribute?

由 旧巷老猫 提交于 2019-12-10 09:37:03
问题 I'm trying to show add some filters on my store, but they have a nasty side effect. Suppose I have product type A and B. Now I want to only show A where color = blue/red. $collection = Mage::getResourceModel('catalog/product_collection') ->setStoreId($this->getStoreId()) ->addCategoryFilter($this) ->addAttributeToFilter(array( array('attribute' => 'color', 'in' => array(4, 6)), ) ); This does the trick, but now because product type B has no value assigned to color(since this attribute isn't

Which is faster, EXISTS before or after the INSERT?

由 情到浓时终转凉″ 提交于 2019-12-10 03:03:53
问题 I have an SP in SQL Server which runs hundreds of times a minute, and needs to check incoming traffic against a database. At the moment it does the following INSERT INTO table SELECT @value1,@value2 WHERE NOT EXISTS (SELECT * FROM table WHERE value1 = @value1 AND value2 = @value2); However, I could also go with IF NOT EXISTS(SELECT * FROM table WHERE value1 = @value1 AND value2 = @value2) INSERT INTO table (value1,value2) VALUES (@value1,@value2); Which would be faster? I get the feeling

Component series.liquidFill not exists. Load it first.

由 て烟熏妆下的殇ゞ 提交于 2019-12-09 17:39:13
vue 项目中使用水波球报错Component series.liquidFill not exists. Load it first. 解决办法：安装 echarts-liquidfill npm install echarts-liquidfill --save 组件中引入： import echarts from "echarts/lib/echarts" import 'echarts-liquidfill' 来源： https://www.cnblogs.com/lyt0207/p/12012286.html
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