Queries

Queries – 查询

Queries are the output of a QL program. They evaluate to sets of results.

Queries是QL程序的输出，执行的结果集合。

There are two kinds of queries. For a given query module, the queries in that module are:

有两种Queries。对于给定的查询模块，该模块中的查询是

• The select clause, if any, defined in that module.

• select 子句（如果有的话）在该模块中定义。

• Any query predicates in that module’s predicate namespace. That is, they can be defined in the module itself, or imported from a different module.

• 在该模块的谓词空间中的任何查询谓词，也就是说，它们可以在模块本身定义，也可以从其他模块导入

We often also refer to the whole QL program as a query.

通常也把整个QL程序称为查询。

Select clauses

When writing a query module, you can include a select clause (usually at the end of the file) of the following form:

在编写查询模块时，你可以包含一个选择子句（通常在文件的末尾），其形式如下:

(from 和 where 部分可以省略)

from /* ... variable declarations ... */
where /* ... logical formula ... */
select /* ... expressions ... */

Apart from the expressions described in “Expressions,” you can also include:

除了 “表达式 “中描述的表达式外，你还可以包括:

• The as keyword, followed by a name. This gives a “label” to a column of results, and allows you to use them in subsequent select expressions.

• as关键字，后面跟着一个名字。这给一列结果打上了 “标签”，并允许你在随后的选择表达式中使用它们。

• The order by keywords, followed by the name of a result column, and optionally the keyword asc or desc. This determines the order in which to display the results.

• ORDER BY关键字，后跟结果列的名称，还可以选择关键字asc或desc 。这决定了显示结果的顺序。

Queries.ql

from int x, int y
where x = 3 and y in [0 .. 2]
select x, y, x * y as product, "product: " + product

from int x, int y
where x = 3 and y in [0 .. 2]
select x, y, x * y as product, "product: " + product
as res order by  res desc

Query predicates – 查询谓词

A query predicate is a non-member predicate with a query annotation. It returns all the tuples that the predicate evaluates to.

查询谓词是具有查询注释的非成员谓词。 它返回谓词求值的所有元组。

个人理解。再非成员谓词前面加上一个 query注释就代表这个非成员谓词是要被查询的，如果不加query 注释就会报错

Queries1.ql

query int getProduct(int x, int y) {
  x = 3 and
  y in [0 .. 2] and
  result = x * y
}

A benefit of writing a query predicate instead of a select clause is that you can call the predicate in other parts of the code too. For example, you can call getProduct inside the body of a class:

编写查询谓词而不是选择子句(select clause)的一个好处是，你也可以在代码的其他部分调用该谓词。

Queries2.ql

query int getProduct(int x, int y) {
    x = 4 and
    y in [0 .. 3] and
    result = x * y
  }

class MultipleOfThree extends int {
    MultipleOfThree() { this = getProduct(_, _) }
}