exists

【转帖】分布式事务之解决方案（XA和2PC）

由 China☆狼群 提交于 2019-12-20 07:30:51
分布式事务之解决方案（XA和2PC） https://zhuanlan.zhihu.com/p/93459200 ​ 博彦信息技术有限公司 java工程师 3. 分布式事务解决方案之2PC（两阶段提交） 针对不同的分布式场景业界常见的解决方案有2PC、TCC、可靠消息最终一致性、最大努力通知这几种。 3.1. 什么是2PC 2PC即两阶段提交协议，是将整个事务流程分为两个阶段，准备阶段（Prepare phase）、提交阶段（commit phase），2是指两阶段，P是指准备阶段，C是提交阶段。 举例 ：张三和李四好久不见，老友约起聚餐，饭店老板要求先买单，才能出票。这时张三和李四分别抱怨近况不如意，囊肿羞涩，都不愿意请客，这时只能AA。只有张三和李四都付款，老板才能出票安排就餐。但由于张三和李四都是铁公鸡，形成两尴尬的一幕 ： 准备阶段 ：老板要求张三付款，张三付款。老板要求李四付款，李四付款。 提交阶段 ：老板出票，两人拿票纷纷落座就餐。 例子中形成两一个事务，若张三或李四其中一个拒绝付款，或钱不够，店老板都不会给出票，并且会把已收款退回。 整个事务过程由事务管理器和参与者组成，店老板就是事务管理器，张三、李四就是事务参与者，事务管理器负责决策整个分布式事务的提交和回滚，事务参与者负责自己本地事务的提交和回滚。 在计算机中部分关系数据库如Oracle

[Amazon](500310) Invalid operation: This type of IN/NOT IN query is not supported yet;

由 自作多情 提交于 2019-12-20 05:47:21
问题 I'm converting this query from Netezza to run with my RedShift dw. I'm continuously getting this error. Amazon Invalid operation: This type of IN/NOT IN query is not supported yet; I have tried converting it using 'EXISTS/NOT EXISTS' condition but still not successful. Can someone give his/her input how should i convert that IN, NOT IN part? CREATE TEMP TABLE TMP_EMPLY_BRND AS ( Select EMPLY_SRRGT_ID, EMPLY_PRMRY_BRND_PRDCT_DPRTMNT_EFF_STRT_DT_KEY, EMPLY_PRMRY_PRDCT_DPRTMNT_GRP_SRRGT_ID, From

Shuold I use not exists or join statement to filter out NULLs?

由 你说的曾经没有我的故事 提交于 2019-12-20 04:28:19
问题 SELECT * FROM employees e WHERE NOT EXISTS ( SELECT name FROM eotm_dyn d WHERE d.employeeID = e.id ) And SELECT * FROM employees a LEFT JOIN eotm_dyn b on (a.joinfield=b.joinfield) WHERE b.name IS NULL Which is more efficient,some analysis? 回答1: Assuming the column values involved can not be NULL - MySQL: LEFT JOIN/IS NULL is more efficient than NOT EXISTS - read this article for details. Oracle: They are equivalent. SQL Server: NOT EXISTS is more efficient than LEFT JOIN/IS NULL - read this

MS Access Insert where not exists

由 不问归期 提交于 2019-12-20 03:17:02
问题 I have the following table: +-----------+--------+ | FirstName | Active | +-----------+--------+ | Rob | TRUE | | Jason | TRUE | | Mike | FALSE | +-----------+--------+ I would like to insert 'John' (with Active=True) only if an entry for John doesn't exist already where Active=True. I try the following: insert into testTable (FirstName, Active) values ('John',True) where not exists (select 1 from testTable where FirstName='John' and Active=True) but i get 'Query input must contain at least

Check if xml node exists in PHP [duplicate]

由 拟墨画扇 提交于 2019-12-19 05:23:11
问题 This question already has answers here : php SimpleXML check if a child exists (15 answers) Closed 5 years ago . I have this simplexml result object: object(SimpleXMLElement)#207 (2) { ["@attributes"]=> array(1) { ["version"]=> string(1) "1" } ["weather"]=> object(SimpleXMLElement)#206 (2) { ["@attributes"]=> array(1) { ["section"]=> string(1) "0" } ["problem_cause"]=> object(SimpleXMLElement)#94 (1) { ["@attributes"]=> array(1) { ["data"]=> string(0) "" } } } } I need to check if the node

Check if xml node exists in PHP [duplicate]

由 二次信任 提交于 2019-12-19 05:23:05
问题 This question already has answers here : php SimpleXML check if a child exists (15 answers) Closed 5 years ago . I have this simplexml result object: object(SimpleXMLElement)#207 (2) { ["@attributes"]=> array(1) { ["version"]=> string(1) "1" } ["weather"]=> object(SimpleXMLElement)#206 (2) { ["@attributes"]=> array(1) { ["section"]=> string(1) "0" } ["problem_cause"]=> object(SimpleXMLElement)#94 (1) { ["@attributes"]=> array(1) { ["data"]=> string(0) "" } } } } I need to check if the node

Linq To Entities - Any VS First VS Exists

由 你。 提交于 2019-12-19 05:12:28
问题 I am using Entity Framework and I need to check if a product with name = "xyz" exists ... I think I can use Any(), Exists() or First(). Which one is the best option for this kind of situation? Which one has the best performance? Thank You, Miguel 回答1: Any translates into "Exists" at the database level. First translates into Select Top 1 ... Between these, Exists will out perform First because the actual object doesn't need to be fetched, only a Boolean result value. At least you didn't ask

Linq To Entities - Any VS First VS Exists

由 只愿长相守 提交于 2019-12-19 05:12:02
问题 I am using Entity Framework and I need to check if a product with name = "xyz" exists ... I think I can use Any(), Exists() or First(). Which one is the best option for this kind of situation? Which one has the best performance? Thank You, Miguel 回答1: Any translates into "Exists" at the database level. First translates into Select Top 1 ... Between these, Exists will out perform First because the actual object doesn't need to be fetched, only a Boolean result value. At least you didn't ask

Oracle sql return true if exists question

由 别来无恙 提交于 2019-12-19 05:07:21
问题 How do I check if a particular element exists in a table - how can I return true or false? I have a table that has user_id user_password user_secretQ Verbally, I want to do this: If a particular user_id exists in the user_id column, then return true -- otherwise return false. 回答1: There is no Boolean type in Oracle SQL. You will need to return a 1 or 0, or some such and act accordingly: SELECT CASE WHEN MAX(user_id) IS NULL THEN 'NO' ELSE 'YES' END User_exists FROM user_id_table WHERE user_id

how to say create procedure if not exist in MySQL

由 半腔热情 提交于 2019-12-18 18:40:02
问题 I am trying to write a script to create a procedure in MySQL database, but I want to check if it exsit first. I know how to do it for a table, but when I use the same syntax for stored procedure, it doesn't compile. Does anybody know? Thanks 回答1: Just drop the procedure if it does exist and then re-add it: DROP PROCEDURE IF EXISTS my_procedure; CREATE PROCEDURE my_procedure() 回答2: SELECT EXISTS(SELECT 1 FROM mysql.proc p WHERE db = 'db_name' AND name = 'stored_proc_name'); So you could do: IF
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