Question

我希望在from子句中获取所有子查询，但是当我使用

时

private bool IsInputDateMatch(InputDate inputDate, DateTime date)
{
    if (inputDate.Day != 0 && date.Day != inputDate.Day)
        return false;

    if (inputDate.Month != 0 && date.Month != inputDate.Month)
        return false;

    return inputDate.Year == 0 || date.Year == inputDate.Year;
}

它只检索from子句中的第一个子查询，当我使用

时

 FromItem fromItems = plainSelect.getFromItem();

它检索from语句中的表而不是Sub查询。

Answer 1

所以这里有一个小代码剪断。您必须知道，第一个表/子选择存储在PlainSelect的fromItem中以及连接中的以下内容中。你必须处理两者。这是由于JSqlParser使用的解析架构。

在JSqlParser中，您有两种类型遍历返回的对象层次结构：1。访问者模式，2。直接对象层次结构访问。我在这个小例子中实现了两个。

编辑：为了找到JSqlParser标识的分层所有子查询，我包含了类型3，这是一种黑客行为，因为我不知何故错过了deparser。

public class SimpleSqlParser10 {
    public static void main(String args[]) throws JSQLParserException {
        String sql = "SELECT * FROM myTable, (select * from myTable2) as data1, (select b from myTable3) as data2";
        Select select = (Select)CCJSqlParserUtil.parse(sql);
        System.out.println(select.toString());


        System.out.println("Type 1: Visitor processing");
        select.getSelectBody().accept(new SelectVisitorAdapter(){
            @Override
            public void visit(PlainSelect plainSelect) {
                plainSelect.getFromItem().accept(fromVisitor);
                if (plainSelect.getJoins()!=null)
                   plainSelect.getJoins().forEach(join -> join.getRightItem().accept(fromVisitor));
            }
        });

        System.out.println("Type 2: simple method calls");
        processFromItem(((PlainSelect)select.getSelectBody()).getFromItem());
        if (((PlainSelect)select.getSelectBody()).getJoins()!=null)
            ((PlainSelect)select.getSelectBody()).getJoins().forEach(join -> processFromItem(join.getRightItem()));


        System.out.println("Type 3: hierarchically process all subselects");
        select.getSelectBody().accept(new SelectDeParser() {
            @Override
            public void visit(SubSelect subSelect) {
                System.out.println("  found subselect=" + subSelect.toString());
                super.visit(subSelect);             }
        });
    }

    private final static FromItemVisitorAdapter fromVisitor = new FromItemVisitorAdapter() {
        @Override
        public void visit(SubSelect subSelect) {
            System.out.println("subselect=" + subSelect);
        }

        @Override
        public void visit(Table table) {
            System.out.println("table=" + table);
        }
    } ;

    private static void processFromItem(FromItem fromItem) {
        System.out.println("fromItem=" + fromItem);
    }
}

这个输出

SELECT * FROM myTable, (SELECT * FROM myTable2) AS data1, (SELECT b FROM myTable3) AS data2
Type 1: Visitor processing
table=myTable
subselect=(SELECT * FROM myTable2) AS data1
subselect=(SELECT b FROM myTable3) AS data2
Type 2: simple method calls
fromItem=myTable
fromItem=(SELECT * FROM myTable2) AS data1
fromItem=(SELECT b FROM myTable3) AS data2
Type 3: hierarchically process all subselects
  found subselect=(SELECT * FROM myTable2) AS data1
  found subselect=(SELECT b FROM myTable3) AS data2

如何使用JSQLparser从“From Clause”获取多个Sub查询？

1 个答案: