Examples of using Exists in Chinese and their translations into English
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SQL关于IN和EXISTS的区别？
Exists，可以用来测试模块的可用性。
NOTIN和NOTEXISTS不是等价的.
Not exists and not in equivalent.Exists()测试一个元素是否在List内.
请注意，Exists的默认值为true。
Note that the default value for Exists is true.我们所要建设的输出语义是existsx.
The output semantics that we want to build is exists x.其他：关系操作，如EXISTS、ISNULL。
Others: Relational operations such as EXISTS, ISNULL.下面这个例子说明了Exists方法的用法。
The following example illustrates the use of the Exists method.如果φ是t类型，x是类型为e的变量，那么existsx.
If φ is of type t, and x is a variable of type e,then exists x. φ and all x.Exists和missing过滤器同样能在内联对象上工作，而不仅仅是核心类型。
The exists and missing filters also work on inner objects, not just core types.如果子查询没有返回任何行，那么EXISTS的结果是"假"。
If the subquery returns no rows, the result of EXISTS is“false”.如果Exists为false，DynamoDB将假设表中not存在属性值。
If Exists is false, DynamoDB assumes that the attribute value does not exist in the table.在这种情况下，使用EXISTS(或NOTEXISTS)通常将提高查询的效率。
In this case, use the EXISTS(or NOT EXISTS) will usually improve the query efficiency.例如像EXISTS或者SISMEMBER这样的命令会在true的时候返回1，false的时候返回0。
For instance commands like EXISTS or SISMEMBER will return 1 for true and 0 for false.最早知道Galloway，是因为他的博士论文《Protocol:HowControlExistsAfterDecentralization》。
As Galloway emphasizes, Protocol is how control exists after decentralization.可选的IFEXISTS子句抑制表不存在时通常会导致的错误。
The optional IF EXISTS clause suppresses the error that would normally result if the table does not exist.Exists()用于确定是否已经将特定字段值加载到数据加载脚本中的字段。
Exists() determines whether a specific field value has already been loaded into the field in the data load script.另一方面，exists则会检查文件是否存在，如果存在则激活profile。
On the other hand exists will test for the existence of the file and if it is there the profile will be activated.Exists-促使DynamoDB在尝试条件运算之前计算值的Boolean值。
Exists- A Boolean value that causes DynamoDB to evaluate the value before attempting the conditional operation:.存在量词的相应的符号是∃，它是反过来的字母E，表示单词“exists”。
The corresponding symbol for the existential quantifieris"∃," a rotated letter"E," which stands for the word"exists.".如果Exists为true，则DynamoDB将检查以了解表中是否已存在属性值。
If Exists is true, DynamoDB will check to see if that attribute value already exists in the table.存在量词的相应的符号是∃，它是反过来的字母E，表示单词“exists”。
The corresponding symbol for the existential quantifier is"∃", a rotated letter"E",which stands for"there exists" or"exists".Thiscostalwaysexistswhentheproductionofaseriesisstarted.开始时，总是存在着一系列的生产成本。
This cost always exists when the production of a series is started.[$/production].所以我们是怎么使用exists或missing来检测name字段的呢，这个字段并没有真正存在于倒排索引中。?
So how can we use an exists or missing filter on the name field, which doesn't really exist in the inverted index?很多时候用exists代替in是一个好的选择：selectnumfromawherenumin(selectnumfromb)，用下面的语句替换：selectnumfromawhereexists(select1frombwherenum=a.num)。
Many times replacing in with exists is a good choice: Select num from a where num in(select num from B).那么我们如何用exists或missing查询name字段呢？name字段并不真实存在于倒排索引中。?
So how can we use an exists or missing query on the name field, which doesn't really exist in the inverted index?用费奇符号可记为:Q(a)→∃xQ(x){\displaystyleQ(a)\to\\exists{x}\,Q(x)}常量小写a在Q(x)中代替了所有自由变量。
In the Fitch-style calculus: Q( a)→∃ x Q(x){\displaystyle Q(a)\to\\exists{x}\, Q(x)} Where a replaces all free instances of x within Q(x).很多时候用exists代替in是一个好的选择：selectnumfromawherenumin(selectnumfromb).
Many times replacing in with exists is a good choice: Select num from a where num in(select num from B).一个变量被称为在一个公式中自由出现，如果它只出现于不在量词∀{\displaystyle\forall}或∃{\displaystyle\exists}作用域内的公式中，.
A variable is said to occur free within a formula if it occurs outside the scope of quantifiers∀{\displaystyle\forall}or∃{\displaystyle\exists}.注意：对于NULL集合，EXISTS是唯一一个不会引发COLLECTION_IS_NULL异常的方法。
With a null collection, EXISTS is the only collection method that does not raise the predefined exception COLLECTION_IS_NULL.
