db2实现查询表中所有字段数据并计算其中三个VARCHAR类型且可能为空的字段值除以3得到的平均值并保留2位小数

在DB2数据库中，处理这个问题需要使用动态SQL或者存储过程，因为我们需要遍历表的所有列并检查其数据类型。以下是一个示例，使用存储过程实现这一需求：

CREATE OR REPLACE PROCEDURE calculate_average_vARCHAR (
    @table_name VARCHAR(128),
    @column_names VARCHAR(MAX)
) AS LANGUAGE SQLSCRIPT DETERMINISTIC NOEXCEPTION NAME 'CALCULATE_AVERAGE_VARCHAR'
BEGIN ATOMIC
   DECLARE @total DECIMAL(10, 2);
   DECLARE @count INT DEFAULT 0;

   DECLARE col_cursor CURSOR FOR
   VALUES UNNESTSTRING(@column_names);

   OPEN col_cursor;
   
   FETCH NEXT FROM col_cursor INTO @column_name;

   WHILE (@@FETCH_STATUS = 0) DO
      -- 只考虑VARCHAR类型的字段
      IF DATA_TYPE_OF(@column_name) = 'CHAR' OR DATA_TYPE_OF(@column_name) = 'VARCHAR' THEN
         SET @total = @total + COALESCE((SELECT CAST(SUBSTRING(@column_name, 1, 3) AS DECIMAL) FROM TABLE(@table_name) WHERE LENGTH(@column_name) > 2), 0); -- 取前三位字符，忽略空值
         SET @count = @count + 1;
      END IF;

      FETCH NEXT FROM col_cursor INTO @column_name;
   END WHILE;

   CLOSE col_cursor;
   
   IF @count > 0 THEN
      SET @total = @total / @count;
      EXECUTE IMMEDIATE 'SELECT FORMATdecimal(:1, 2) AS "Average VARCHAR Value" FROM SYSIBM.SYSDUMMY1' USING @total;
   ELSE
      RAISE_APPLICATION_ERROR(-20001, 'No valid VARCHAR data found for calculation.');
   END IF;
END @CALCULATE_AVERAGE_VARCHAR;

CALL CALCULATE_AVERAGE_VARCHAR('your_table', 'field1,field2,field3');

请替换 'your_table' 和 'field1,field2,field3' 为实际的表名和字段名。