subquery
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例句
Within the body of a subquery, it is often necessary to refer to the value of a column in the active row of the main query.
在子查询的正文中，通常需要引用主查询的活动行中的列的值。
A reference to columns or expressions in the main table(s) is called an outer reference and the subquery is said to be correlated.
对主表中的列或表达式的引用被称作外部引用，并且这种子查询是相关的。
The EXISTS condition is TRUE if the subquery result contains at least one row, and FALSE if the subquery result does not contain any rows.
如果子查询结果至少包含一行，则EXISTS条件为TRUE；如果子查询结果一行也不包含，则条件为FALSE。
Multiple references to such columns in a subquery do not cause the functions to be evaluated multiple times.
在子查询中对这些列的多次引用不会使这些函数被计算多次。
Number of optimizations for a query that contains at least one subquery.
包含至少一个子查询的查询的优化数。
Two types of queries can be used in the WHERE clause of an UPDATE statement: a scalar subquery and a table subquery.
两种查询可以用于UPDATE语句的WHERE子句中：标量子查询和表子查询。
The result of the scalar subquery first needs to be transferred to the federated server.
首先需要将标量子查询的结果传送到联邦服务器。
The IN operator is one of four SQL operators that you can use with a table subquery.
IN操作符是可以用于表子查询的四个SQL操作符之一。
If the subquery (which must have one column) returns one row, then the value of that row is compared to the expression.
如果子查询（必须含有一列）返回一行，则该行的值将与表达式进行比较。
Casts may be required if the columns of the initial subquery do not have the same domains as those of the recursive subquery.
如果初始子查询的列与递归子查询的列具有不同的域，则可能需要进行转换。
Any null values returned by subquery or expression that are compared to test_expression using IN or NOT IN return UNKNOWN.
subquery或expression使用IN或NOTIN与test_expression比较后返回的所有空值都将返回UNKNOWN。
Is a constant, function, any combination of column names, constants, and functions connected by an operator or operators, or a subquery.
常量、函数以及由一个或多个运算符连接的列名、常量和函数的任意组合，或者是子查询。
A subquery that references one or more columns from its containing SQL statement is called a correlated subquery.
如果一个子查询中引用了包含查询语句的一个或多个字段，则该子查询就称为相关性子查询。
The SHIP3 operator contains the statement that shows the result of the scalar subquery being bound in as a host variable.
SHIP3操作符包含一个语句，该语句表明标量子查询的结果放在一个主机变量中。
The query above contains a correlated subquery, since the main query and the subquery are relaying on the same table, the employees table.
以上查询包含一个相关子查询，因为主查询和子查询依靠于同一个表，即employees表。
The last section also describes the ALL, EXISTS, and SOME or ANY predicates, which can be used to express conditions on subquery results.
最后一节还描述了ALL、EXISTS和SOME或ANY谓词，这些谓词可用于表达子查询结果上的条件。
The main query does not contain a GROUP BY clause, and is not an aggregate query, or the subquery returns exactly one value.
主查询不包含GROUPBY子句并且不是汇总查询，或者子查询恰好返回一个值。
The number of times the subquery and its function is executed can vary with different access paths chosen by the optimizer.
子查询及其函数执行的次数会因优化器选择的访问路径的不同而异。
The first is the unnesting of the subquery into a join between the employee and sales_order tables.
第一个优化解除了职员与sales_order表之间连接中的子查询嵌套。
This extension, specifying a join, can be used instead of a subquery in the WHERE clause to identify rows to be removed.
这个扩展指定联接，可在WHERE子句中取代子查询来标识要删除的行。
The expression can be a constant or a column name, and the list can be a set of constants or, more commonly, a subquery.
该表达式可以是一个常量或一个列名，而列表可以是一组常量，通常为一个子查询。
The database server automatically attempts to convert the values returned by the recursive subquery to match those of the initial query.
数据库服务器会自动尝试转换由递归子查询返回的值，以便与初始查询的那些值匹配。
In this case, error 1242 means that the query execution failed because there was a problem in a subquery.
在这里，错误1242表示查询操作失败，由于子查询有问题。
The previous subquery in this statement cannot be evaluated independently of the outer query.
该语句中前面的子查询无法独立于外部查询进行计算。
Used with a subquery to test for the existence of rows returned by the subquery.
与子查询一起使用，用于测试是否存在子查询返回的行。
The only change we made here was to get rid of the subquery in the original qeury.
这里我们所做的惟一更改就是去掉了原始查询中的子查询。
Specifies the name of the table, view, user-defined function, or subquery for the associated data column.
指定表、视图、用户定义函数或关联数据列的子查询的名称。
EXISTS Use EXISTS in a WHERE clause to indicate that a subquery should return at least one row.
EXISTS在WHERE子句中使用EXISTS可以指示子查询至少应该返回一行。
The SELECT subquery in the INSERT statement can be used to add values into a table from one or more other tables or views.
INSERT语句中的SELECT子查询可用于将一个或多个表或视图中的值添加到另一个表中。
Thus, a subquery can be thought of as a temporary table with statement scope.
因此，一个子查询可以认为是语句范围内的临时表（内联视图）。
Specifies the conditions for the rows returned in the result set for a SELECT statement, query expression, or subquery.
指定要在SELECT语句、查询表达式或子查询的结果集中返回的行的条件。
Explicit casts may also be required when the initial subquery selects values from different columns than the recursive subquery.
当初始子查询从与递归子查询不同的列中选择值时，也可能需要进行显式转换。
ALL Use ALL in a WHERE clause to retrieve rows that satisfy the condition when compared to every row returned by the subquery.
ALL在WHERE子句中使用ALL，可以检索在与子查询返回的每个行进行比较时满足条件的行。
A subquery can appear anywhere an expression can be used, if it returns a single value.
任何可以使用表达式的地方都可以使用子查询，只要它返回的是单个值。
The expression in the following table is one example of a calculated field that results from a subquery.
下表中的表达式便是使用子查询生成计算字段的一个示例。
If your application requires a row filter to use a subsquery, ensure that the subquery only references lookup data that does not change.
如果您的应用程序要求行筛选器使用子查询，请确保子查询仅引用不发生更改的查找数据。
The expression cannot be a subquery or include an alias data type.
表达式不能是子查询，也不能包含别名数据类型。
You do not have to try this approach with queries that contain the IN subquery clause.
对包含IN子查询子句的查询，不必使用此方法。
The subscription_list column is used for log scanning and the subquery is used for extraction and synchronization.
subscription_list列用于日志扫描，子查询用于抽取和同步。
The subquery in this statement is absurdly simple, and completely unnecessary, but it does serve to illustrate a point.
这个子查询非常简单，并且完全没有必要，但是它能说明一点。
