MacLochlainns Weblog

Every now and then, I get questions from folks about how to tune in-memory elements of their PL/SQL programs. This blog post address one of those core issues that some PL/SQL programmers avoid.

Specifically, it addresses how to convert a list of values into a structure (in C/C++ its a struct, in Java its an ArrayList, and PL/SQL it’s a table of scalar or object types). Oracle lingo hides the similarity by calling either an Attribute Definition Type (ADT) or User-Defined Type (UDT). The difference in the Oracle space is that an ADT deals with a type defined in DBMS_STANDARD package, which is more or less like a primitive type in Java.

Oracle does this for two reasons:

• They handle lists of standard types in a difference C++ class than they do UDT types.
• They rigidly adhere to Interface Definition Language (IDL) principles.

The cast_strings function converts a list of strings into a record data structure. It lets the list of strings have either a densely or sparsely populated list of values, and it calls the verify_date function to identify a DATE data type and regular expressions to identify numbers and strings.

You need to build a UDT object type and lists of both ADT and UDT data types.

/* Create a table of strings. */
CREATE OR REPLACE
  TYPE tre AS TABLE OF VARCHAR2(20);
/
 
/* Create a structure of a date, number, and string. */
CREATE OR REPLACE
  TYPE struct IS OBJECT
  ( xdate     DATE
  , xnumber  NUMBER
  , xstring  VARCHAR2(20));
/
 
/* Create a table of tre type. */
CREATE OR REPLACE
  TYPE structs IS TABLE OF struct;
/

The cast_strings function is defined below:

CREATE OR REPLACE
  FUNCTION cast_strings
  ( pv_list  TRE ) RETURN struct IS
 
  /* Declare a UDT and initialize an empty struct variable. */
  lv_retval  STRUCT := struct( xdate => NULL
                             , xnumber => NULL
					         , xstring => NULL); 
  BEGIN  
    /* Loop through list of values to find only the numbers. */
    FOR i IN 1..pv_list.LAST LOOP
      /* Ensure that a sparsely populated list can't fail. */
      IF pv_list.EXISTS(i) THEN
        /* Order if number evaluation before string evaluation. */
        CASE
          WHEN lv_retval.xnumber IS NULL AND REGEXP_LIKE(pv_list(i),'^[[:digit:]]*$') THEN
            lv_retval.xnumber := pv_list(i);
          WHEN verify_date(pv_list(i)) THEN
            IF lv_retval.xdate IS NULL THEN
              lv_retval.xdate := pv_list(i);
            ELSE
              lv_retval.xdate := NULL;
            END IF;
          WHEN lv_retval.xstring IS NULL AND REGEXP_LIKE(pv_list(i),'^[[:alnum:]]*$') THEN
            lv_retval.xstring := pv_list(i);
          ELSE
            NULL;
        END CASE;
      END IF;
    END LOOP;
 
    /* Print the results. */
    RETURN lv_retval;
  END;
/

There are three test cases for this function:

• The first use-case checks whether the input parameter is a sparsely or densely populated list:

  DECLARE /* Declare an input variable of three or more elements. */ lv_list TRE := tre('Berlin','25','09-May-1945','45');   /* Declare a variable to hold the compound type values. */ lv_struct STRUCT; BEGIN /* Make the set sparsely populated. */ lv_list.DELETE(2);   /* Test the cast_strings function. */ lv_struct := cast_strings(lv_list);   /* Print the values of the compound variable. */ dbms_output.put_line(CHR(10)); dbms_output.put_line('xstring ['||lv_struct.xstring||']'); dbms_output.put_line('xdate ['||TO_CHAR(lv_struct.xdate,'DD-MON-YYYY')||']'); dbms_output.put_line('xnumber ['||lv_struct.xnumber||']'); END; /

  DECLARE /* Declare an input variable of three or more elements. */ lv_list TRE := tre('Berlin','25','09-May-1945','45'); /* Declare a variable to hold the compound type values. */ lv_struct STRUCT; BEGIN /* Make the set sparsely populated. */ lv_list.DELETE(2); /* Test the cast_strings function. */ lv_struct := cast_strings(lv_list); /* Print the values of the compound variable. */ dbms_output.put_line(CHR(10)); dbms_output.put_line('xstring ['||lv_struct.xstring||']'); dbms_output.put_line('xdate ['||TO_CHAR(lv_struct.xdate,'DD-MON-YYYY')||']'); dbms_output.put_line('xnumber ['||lv_struct.xnumber||']'); END; /

  It should return:

  xstring [Berlin] xdate [09-MAY-1945] xnumber [45]

  xstring [Berlin] xdate [09-MAY-1945] xnumber [45]

  The program defines two numbers and deletes the first number, which is why it prints the second number.

• The second use-case checks with a list of only one element:

  SELECT TO_CHAR(xdate,'DD-MON-YYYY') AS xdate , xnumber , xstring FROM TABLE(structs(cast_strings(tre('catch22','25','25-Nov-1945'))));

  SELECT TO_CHAR(xdate,'DD-MON-YYYY') AS xdate , xnumber , xstring FROM TABLE(structs(cast_strings(tre('catch22','25','25-Nov-1945'))));

  It should return:

  XDATE XNUMBER XSTRING -------------------- ---------- -------------------- 25-NOV-1945 25 catch22

  XDATE XNUMBER XSTRING -------------------- ---------- -------------------- 25-NOV-1945 25 catch22

  The program returns a structure with values converted into their appropriate data type.

• The third use-case checks with a list of two elements:

  SELECT TO_CHAR(xdate,'DD-MON-YYYY') AS xdate , xnumber , xstring FROM TABLE(structs(cast_strings(tre('catch22','25','25-Nov-1945')) ,cast_strings(tre('31-APR-2017','1918','areodromes'))));

  SELECT TO_CHAR(xdate,'DD-MON-YYYY') AS xdate , xnumber , xstring FROM TABLE(structs(cast_strings(tre('catch22','25','25-Nov-1945')) ,cast_strings(tre('31-APR-2017','1918','areodromes'))));

  It should return:

  XDATE XNUMBER XSTRING -------------------- ---------- -------------------- 25-NOV-1945 25 catch22 1918 areodromes

  XDATE XNUMBER XSTRING -------------------- ---------- -------------------- 25-NOV-1945 25 catch22 1918 areodromes

  The program defines calls the cast_strings with a valid set of values and an invalid set of values. The invalid set of values contains a bad date in the set of values.

As always, I hope this helps those looking for how to solve this type of problem.