How to Compare Data length of staging table with base table definition

Question

Hi,
I've two tables :staging table and base table.
I'm getting data from flatfiles into staging table, as per requirement structure of staging table and base table(length of each and every column in staging table is 25% more to dump data without any errors) are different for ex :if we've city column with varchar length 40 in staging table it has 25 in base table.Once data is dumped into staging table I want to compare actual data length of each and every column in staging table with definition of base table(data_length for each and every column from all_tab_columns) and if any column differs length I need to update the corresponding row in staging table which also has a flag called err_length.
so for this I'm using cursor c1 is select length(a.id),length(a.name)... from staging_table;
cursor c2(name varchar2) is select data_length from all_tab_columns where table_name='BASE_TABLE' and column_name=name;
But we're getting data atonce in first query whereas in second cursor I need to get each and every column and then compare with first ?
Can anyone tell me how to get desired results?
Thanks,
Mahender.

Answer 1

This is a shot in the dark but, take a look at this example below:
SQL> DROP TABLE STAGING;
Table dropped.
SQL> DROP TABLE BASE;
Table dropped.
SQL> CREATE TABLE STAGING
  2  (
  3          ID              NUMBER
  4  ,       A               VARCHAR2(40)
  5  ,       B               VARCHAR2(40)
  6  ,       ERR_LENGTH      VARCHAR2(1)
  7  );
Table created.
SQL> CREATE TABLE BASE
  2  (
  3          ID      NUMBER
  4  ,       A       VARCHAR2(25)
  5  ,       B       VARCHAR2(25)
  6  );
Table created.
SQL> INSERT INTO STAGING VALUES (1,RPAD('X',26,'X'),RPAD('X',25,'X'),NULL);
1 row created.
SQL> INSERT INTO STAGING VALUES (2,RPAD('X',25,'X'),RPAD('X',26,'X'),NULL);
1 row created.
SQL> INSERT INTO STAGING VALUES (3,RPAD('X',25,'X'),RPAD('X',25,'X'),NULL);
1 row created.
SQL> COMMIT;
Commit complete.
SQL> SELECT * FROM STAGING;
        ID A                                        B                                        E
         1 XXXXXXXXXXXXXXXXXXXXXXXXXX               XXXXXXXXXXXXXXXXXXXXXXXXX
         2 XXXXXXXXXXXXXXXXXXXXXXXXX                XXXXXXXXXXXXXXXXXXXXXXXXXX
         3 XXXXXXXXXXXXXXXXXXXXXXXXX                XXXXXXXXXXXXXXXXXXXXXXXXX
SQL> UPDATE  STAGING ST
  2  SET     ERR_LENGTH = 'Y'
  3  WHERE   EXISTS
  4          (
  5                  WITH    columns_in_staging AS
  6                  (
  7                          /* Retrieve all the columns names for the staging table with the exception of the primary key column
  8                           * and order them alphabetically.
  9                           */
10                          SELECT  COLUMN_NAME
11                          ,       ROW_NUMBER() OVER (ORDER BY COLUMN_NAME) RN
12                          FROM    ALL_TAB_COLUMNS
13                          WHERE   TABLE_NAME='STAGING'
14                          AND     COLUMN_NAME != 'ID'
15                          ORDER BY 1
16                  ),      staging_unpivot AS
17                  (
18                          /* Using the columns_in_staging above UNPIVOT the result set so you get a record for each COLUMN value
19                           * for each record. The DECODE performs the unpivot and it works if the decode specifies the columns
20                           * in the same order as the ROW_NUMBER() function in columns_in_staging
21                           */
22                          SELECT  ID
23                          ,       COLUMN_NAME
24                          ,       DECODE
25                                  (
26                                          RN
27                                  ,       1,A
28                                  ,       2,B
29                                  )  AS VAL
30                          FROM            STAGING
31                          CROSS JOIN      COLUMNS_IN_STAGING
32                  )
33                  /*      Only return IDs for records that have at least one column value that exceeds the length. */
34                  SELECT  ID
35                  FROM
36                  (
37                          /* Join the unpivoted staging table to the ALL_TAB_COLUMNS table on the column names. Here we perform
38                           * the check to see if there are any differences in the length if so set a flag.
39                           */
40                          SELECT  STAGING_UNPIVOT.ID
41                          ,       (CASE WHEN ATC.DATA_LENGTH < LENGTH(STAGING_UNPIVOT.VAL) THEN 'Y' END) AS ERR_LENGTH_A
42                          ,       (CASE WHEN ATC.DATA_LENGTH < LENGTH(STAGING_UNPIVOT.VAL) THEN 'Y' END) AS ERR_LENGTH_B
43                          FROM    STAGING_UNPIVOT
44                          JOIN    ALL_TAB_COLUMNS ATC     ON ATC.COLUMN_NAME = STAGING_UNPIVOT.COLUMN_NAME
45                          WHERE   ATC.TABLE_NAME='BASE'
46                  )       A
47                  WHERE   COALESCE(ERR_LENGTH_A,ERR_LENGTH_B) IS NOT NULL
48                  AND     ST.ID = A.ID
49          )
50  /
2 rows updated.
SQL> SELECT * FROM STAGING;
        ID A                                        B                                        E
         1 XXXXXXXXXXXXXXXXXXXXXXXXXX               XXXXXXXXXXXXXXXXXXXXXXXXX                Y
         2 XXXXXXXXXXXXXXXXXXXXXXXXX                XXXXXXXXXXXXXXXXXXXXXXXXXX               Y
         3 XXXXXXXXXXXXXXXXXXXXXXXXX                XXXXXXXXXXXXXXXXXXXXXXXXXHopefully the comments make sense. If you have any questions please let me know.
This assumes the column names are the same between the staging and base tables. In addition as you add more columns to this table you'll have to add more CASE statements to check the length and update the COALESCE check as necessary.
Thanks!