Question

在这里我需要动态地执行group by子句，在这里如何实现大小写切换

"newProjectRoot": "dashboards",

Answer 1

您需要使SELECT子句中的所有表达式成为聚合函数或GROUP BY子句：

DECLARE
  p_cursor      SYS_REFCURSOR;
  p_start_units VARCHAR2(10) := 'YEAR';
  p_year        NUMBER       := 2019;
  p_month       NUMBER       := 2;

  p_out_month   VARCHAR2(10);
  p_out_count   NUMBER;
BEGIN
  OPEN p_cursor FOR
  SELECT COUNT(*) noofrecords,
         TO_CHAR(
           CASE p_start_units
           WHEN 'YEAR' THEN TRUNC( start_date, 'MM' )
           END,
           'month'
         ) AS value
  FROM   tab_name
  WHERE  EXTRACT(YEAR FROM start_date) = p_year
  AND    CASE 'MONTH'
         WHEN 'MONTH' THEN EXTRACT(MONTH FROM start_date)
         END = p_month
  GROUP BY
         CASE p_start_units
         WHEN 'YEAR' THEN TRUNC( start_date, 'MM' )
         END
  ORDER BY
         CASE p_start_units
         WHEN 'YEAR' THEN TRUNC( start_date, 'MM' )
         END;

  LOOP
    FETCH p_cursor INTO p_out_count, p_out_month;
    EXIT WHEN p_cursor%NOTFOUND;

    DBMS_OUTPUT.PUT_LINE( p_out_month || ': ' || p_out_count );
  END LOOP;
END;
/

测试数据：

CREATE TABLE tab_name ( start_date ) AS
  SELECT DATE '2019-01-01' FROM DUAL UNION ALL
  SELECT DATE '2019-01-01' FROM DUAL UNION ALL
  SELECT DATE '2019-02-01' FROM DUAL UNION ALL
  SELECT DATE '2019-02-01' FROM DUAL UNION ALL
  SELECT DATE '2019-02-01' FROM DUAL UNION ALL
  SELECT DATE '2019-03-01' FROM DUAL;

输出：

february : 3

db <>提琴here

Answer 2

我建议您使用子查询根据变量定义列，然后使用它们进行汇总和排序。

类似这样的东西：

SELECT COUNT(*) as noofrecords, order_by, value
FROM (SELECT t.*,
             TO_CHAR(TO_DATE(EXTRACT(MONTH FROM start_date), 'MM'), 'month') as value
             EXTRACT(MONTH FROM start_date) as order_by
             (CASE 'YEAR'    ----- getting this value from a variable 
                   WHEN 'YEAR' THEN EXTRACT(MONTH FROM start_date)
              END) as grouping_var
    END
             (CASE 'MONTH'  ----- getting this value from a variable
                  WHEN 'MONTH' THEN EXTRACT(MONTH FROM start_date)
              END) as filter_criteria
      FROM tab_name
      WHERE EXTRACT(YEAR FROM start_date) = 2019
     ) t
WHERE filter_column = 2  ----- setting this value from a
GROUP BY grouping_var, order_by, value
ORDER BY order_by;

该查询完全没有意义。但是我怀疑当您将其应用于实际问题时，您会看到这种方法的帮助。

如何在下面的选择查询中使用带有“ case”的group by子句

2 个答案: