Apache Calcite在SQL字符串中查找选定的列 [英] Apache Calcite to Find Selected Columns in an SQL String

问题描述

我有一个用例，我想知道在SQL字符串中选择的列，例如，如果SQL像这样:
SELECT name, age*5 as intelligence FROM bla WHERE bla=bla
然后，在解析了上面的String之后，我只希望输出为:name, intelligence.
首先，可以通过方解石吗?
也欢迎任何其他选择.

I have a use case where I want to know the columns which have been selected in an SQL string.For instance, if the SQL is like this:
SELECT name, age*5 as intelligence FROM bla WHERE bla=bla
Then, after parsing the above String, I just want the output to be: name, intelligence.
Firstly, is it possible through Calcite?
Any other option is also welcome.

PS:在数据库上实际运行查询之前，我想知道这一点.

PS: I want to know this before actually running the query on database.

推荐答案

这对于方解石绝对可行.您首先需要创建SqlParser的实例并解析查询:

This is definitely doable with Calcite. You'll want to start by creating an instance of SqlParser and parsing the query:

SqlParser parser = SqlParser.create(query)
SqlNode parsed = parser.parseQuery()

从那里开始，实现

From there, you'll probably have the most success implementing the SqlVisitor interface. You'll want to first find a SqlSelect instance and then visit each expression being selected by calling visit on each element of getSelectList.

从那里开始，如何进行将取决于您要支持的表达式的复杂性.但是，递归访问所有SqlCall节点及其操作数，然后收集您看到的任何SqlIdentifier值，可能就足够了.

From there, how you proceed will depend on the complexity of expressions you want to support. However, it's probably sufficient to recursively visit all SqlCall nodes and their operands and then collect any SqlIdentifier values that you see.

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