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41.13. Porting from Oracle PL/SQL #

   41.13.1. Porting Examples
   41.13.2. Other Things to Watch For
   41.13.3. Appendix

   This section explains differences between PostgreSQL's PL/pgSQL
   language and Oracle's PL/SQL language, to help developers who port
   applications from Oracle® to PostgreSQL.

   PL/pgSQL is similar to PL/SQL in many aspects. It is a
   block-structured, imperative language, and all variables have to be
   declared. Assignments, loops, and conditionals are similar. The main
   differences you should keep in mind when porting from PL/SQL to
   PL/pgSQL are:
     * If a name used in an SQL command could be either a column name of a
       table used in the command or a reference to a variable of the
       function, PL/SQL treats it as a column name. By default, PL/pgSQL
       will throw an error complaining that the name is ambiguous. You can
       specify plpgsql.variable_conflict = use_column to change this
       behavior to match PL/SQL, as explained in Section 41.11.1. It's
       often best to avoid such ambiguities in the first place, but if you
       have to port a large amount of code that depends on this behavior,
       setting variable_conflict may be the best solution.
     * In PostgreSQL the function body must be written as a string
       literal. Therefore you need to use dollar quoting or escape single
       quotes in the function body. (See Section 41.12.1.)
     * Data type names often need translation. For example, in Oracle
       string values are commonly declared as being of type varchar2,
       which is a non-SQL-standard type. In PostgreSQL, use type varchar
       or text instead. Similarly, replace type number with numeric, or
       use some other numeric data type if there's a more appropriate one.
     * Instead of packages, use schemas to organize your functions into
       groups.
     * Since there are no packages, there are no package-level variables
       either. This is somewhat annoying. You can keep per-session state
       in temporary tables instead.
     * Integer FOR loops with REVERSE work differently: PL/SQL counts down
       from the second number to the first, while PL/pgSQL counts down
       from the first number to the second, requiring the loop bounds to
       be swapped when porting. This incompatibility is unfortunate but is
       unlikely to be changed. (See Section 41.6.5.5.)
     * FOR loops over queries (other than cursors) also work differently:
       the target variable(s) must have been declared, whereas PL/SQL
       always declares them implicitly. An advantage of this is that the
       variable values are still accessible after the loop exits.
     * There are various notational differences for the use of cursor
       variables.

41.13.1. Porting Examples #

   Example 41.9 shows how to port a simple function from PL/SQL to
   PL/pgSQL.

   Example 41.9. Porting a Simple Function from PL/SQL to PL/pgSQL

   Here is an Oracle PL/SQL function:
CREATE OR REPLACE FUNCTION cs_fmt_browser_version(v_name varchar2,
                                                  v_version varchar2)
RETURN varchar2 IS
BEGIN
    IF v_version IS NULL THEN
        RETURN v_name;
    END IF;
    RETURN v_name || '/' || v_version;
END;
/
show errors;

   Let's go through this function and see the differences compared to
   PL/pgSQL:
     * The type name varchar2 has to be changed to varchar or text. In the
       examples in this section, we'll use varchar, but text is often a
       better choice if you do not need specific string length limits.
     * The RETURN key word in the function prototype (not the function
       body) becomes RETURNS in PostgreSQL. Also, IS becomes AS, and you
       need to add a LANGUAGE clause because PL/pgSQL is not the only
       possible function language.
     * In PostgreSQL, the function body is considered to be a string
       literal, so you need to use quote marks or dollar quotes around it.
       This substitutes for the terminating / in the Oracle approach.
     * The show errors command does not exist in PostgreSQL, and is not
       needed since errors are reported automatically.

   This is how this function would look when ported to PostgreSQL:
CREATE OR REPLACE FUNCTION cs_fmt_browser_version(v_name varchar,
                                                  v_version varchar)
RETURNS varchar AS $$
BEGIN
    IF v_version IS NULL THEN
        RETURN v_name;
    END IF;
    RETURN v_name || '/' || v_version;
END;
$$ LANGUAGE plpgsql;

   Example 41.10 shows how to port a function that creates another
   function and how to handle the ensuing quoting problems.

   Example 41.10. Porting a Function that Creates Another Function from
   PL/SQL to PL/pgSQL

   The following procedure grabs rows from a SELECT statement and builds a
   large function with the results in IF statements, for the sake of
   efficiency.

   This is the Oracle version:
CREATE OR REPLACE PROCEDURE cs_update_referrer_type_proc IS
    CURSOR referrer_keys IS
        SELECT * FROM cs_referrer_keys
        ORDER BY try_order;
    func_cmd VARCHAR(4000);
BEGIN
    func_cmd := 'CREATE OR REPLACE FUNCTION cs_find_referrer_type(v_host IN VARC
HAR2,
                 v_domain IN VARCHAR2, v_url IN VARCHAR2) RETURN VARCHAR2 IS BEG
IN';

    FOR referrer_key IN referrer_keys LOOP
        func_cmd := func_cmd ||
          ' IF v_' || referrer_key.kind
          || ' LIKE ''' || referrer_key.key_string
          || ''' THEN RETURN ''' || referrer_key.referrer_type
          || '''; END IF;';
    END LOOP;

    func_cmd := func_cmd || ' RETURN NULL; END;';

    EXECUTE IMMEDIATE func_cmd;
END;
/
show errors;

   Here is how this function would end up in PostgreSQL:
CREATE OR REPLACE PROCEDURE cs_update_referrer_type_proc() AS $func$
DECLARE
    referrer_keys CURSOR IS
        SELECT * FROM cs_referrer_keys
        ORDER BY try_order;
    func_body text;
    func_cmd text;
BEGIN
    func_body := 'BEGIN';

    FOR referrer_key IN referrer_keys LOOP
        func_body := func_body ||
          ' IF v_' || referrer_key.kind
          || ' LIKE ' || quote_literal(referrer_key.key_string)
          || ' THEN RETURN ' || quote_literal(referrer_key.referrer_type)
          || '; END IF;' ;
    END LOOP;

    func_body := func_body || ' RETURN NULL; END;';

    func_cmd :=
      'CREATE OR REPLACE FUNCTION cs_find_referrer_type(v_host varchar,
                                                        v_domain varchar,
                                                        v_url varchar)
        RETURNS varchar AS '
      || quote_literal(func_body)
      || ' LANGUAGE plpgsql;' ;

    EXECUTE func_cmd;
END;
$func$ LANGUAGE plpgsql;

   Notice how the body of the function is built separately and passed
   through quote_literal to double any quote marks in it. This technique
   is needed because we cannot safely use dollar quoting for defining the
   new function: we do not know for sure what strings will be interpolated
   from the referrer_key.key_string field. (We are assuming here that
   referrer_key.kind can be trusted to always be host, domain, or url, but
   referrer_key.key_string might be anything, in particular it might
   contain dollar signs.) This function is actually an improvement on the
   Oracle original, because it will not generate broken code when
   referrer_key.key_string or referrer_key.referrer_type contain quote
   marks.

   Example 41.11 shows how to port a function with OUT parameters and
   string manipulation. PostgreSQL does not have a built-in instr
   function, but you can create one using a combination of other
   functions. In Section 41.13.3 there is a PL/pgSQL implementation of
   instr that you can use to make your porting easier.

   Example 41.11. Porting a Procedure With String Manipulation and OUT
   Parameters from PL/SQL to PL/pgSQL

   The following Oracle PL/SQL procedure is used to parse a URL and return
   several elements (host, path, and query).

   This is the Oracle version:
CREATE OR REPLACE PROCEDURE cs_parse_url(
    v_url IN VARCHAR2,
    v_host OUT VARCHAR2,  -- This will be passed back
    v_path OUT VARCHAR2,  -- This one too
    v_query OUT VARCHAR2) -- And this one
IS
    a_pos1 INTEGER;
    a_pos2 INTEGER;
BEGIN
    v_host := NULL;
    v_path := NULL;
    v_query := NULL;
    a_pos1 := instr(v_url, '//');

    IF a_pos1 = 0 THEN
        RETURN;
    END IF;
    a_pos2 := instr(v_url, '/', a_pos1 + 2);
    IF a_pos2 = 0 THEN
        v_host := substr(v_url, a_pos1 + 2);
        v_path := '/';
        RETURN;
    END IF;

    v_host := substr(v_url, a_pos1 + 2, a_pos2 - a_pos1 - 2);
    a_pos1 := instr(v_url, '?', a_pos2 + 1);

    IF a_pos1 = 0 THEN
        v_path := substr(v_url, a_pos2);
        RETURN;
    END IF;

    v_path := substr(v_url, a_pos2, a_pos1 - a_pos2);
    v_query := substr(v_url, a_pos1 + 1);
END;
/
show errors;

   Here is a possible translation into PL/pgSQL:
CREATE OR REPLACE FUNCTION cs_parse_url(
    v_url IN VARCHAR,
    v_host OUT VARCHAR,  -- This will be passed back
    v_path OUT VARCHAR,  -- This one too
    v_query OUT VARCHAR) -- And this one
AS $$
DECLARE
    a_pos1 INTEGER;
    a_pos2 INTEGER;
BEGIN
    v_host := NULL;
    v_path := NULL;
    v_query := NULL;
    a_pos1 := instr(v_url, '//');

    IF a_pos1 = 0 THEN
        RETURN;
    END IF;
    a_pos2 := instr(v_url, '/', a_pos1 + 2);
    IF a_pos2 = 0 THEN
        v_host := substr(v_url, a_pos1 + 2);
        v_path := '/';
        RETURN;
    END IF;

    v_host := substr(v_url, a_pos1 + 2, a_pos2 - a_pos1 - 2);
    a_pos1 := instr(v_url, '?', a_pos2 + 1);

    IF a_pos1 = 0 THEN
        v_path := substr(v_url, a_pos2);
        RETURN;
    END IF;

    v_path := substr(v_url, a_pos2, a_pos1 - a_pos2);
    v_query := substr(v_url, a_pos1 + 1);
END;
$$ LANGUAGE plpgsql;

   This function could be used like this:
SELECT * FROM cs_parse_url('http://foobar.com/query.cgi?baz');

   Example 41.12 shows how to port a procedure that uses numerous features
   that are specific to Oracle.

   Example 41.12. Porting a Procedure from PL/SQL to PL/pgSQL

   The Oracle version:
CREATE OR REPLACE PROCEDURE cs_create_job(v_job_id IN INTEGER) IS
    a_running_job_count INTEGER;
BEGIN
    LOCK TABLE cs_jobs IN EXCLUSIVE MODE;

    SELECT count(*) INTO a_running_job_count FROM cs_jobs WHERE end_stamp IS NUL
L;

    IF a_running_job_count > 0 THEN
        COMMIT; -- free lock
        raise_application_error(-20000,
                 'Unable to create a new job: a job is currently running.');
    END IF;

    DELETE FROM cs_active_job;
    INSERT INTO cs_active_job(job_id) VALUES (v_job_id);

    BEGIN
        INSERT INTO cs_jobs (job_id, start_stamp) VALUES (v_job_id, now());
    EXCEPTION
        WHEN dup_val_on_index THEN NULL; -- don't worry if it already exists
    END;
    COMMIT;
END;
/
show errors

   This is how we could port this procedure to PL/pgSQL:
CREATE OR REPLACE PROCEDURE cs_create_job(v_job_id integer) AS $$
DECLARE
    a_running_job_count integer;
BEGIN
    LOCK TABLE cs_jobs IN EXCLUSIVE MODE;

    SELECT count(*) INTO a_running_job_count FROM cs_jobs WHERE end_stamp IS NUL
L;

    IF a_running_job_count > 0 THEN
        COMMIT; -- free lock
        RAISE EXCEPTION 'Unable to create a new job: a job is currently running'
; -- (1)
    END IF;

    DELETE FROM cs_active_job;
    INSERT INTO cs_active_job(job_id) VALUES (v_job_id);

    BEGIN
        INSERT INTO cs_jobs (job_id, start_stamp) VALUES (v_job_id, now());
    EXCEPTION
        WHEN unique_violation THEN -- (2)
            -- don't worry if it already exists
    END;
    COMMIT;
END;
$$ LANGUAGE plpgsql;

   (1)

   The syntax of RAISE is considerably different from Oracle's statement,
   although the basic case RAISE exception_name works similarly.

   (2)

   The exception names supported by PL/pgSQL are different from Oracle's.
   The set of built-in exception names is much larger (see Appendix A).
   There is not currently a way to declare user-defined exception names,
   although you can throw user-chosen SQLSTATE values instead.

41.13.2. Other Things to Watch For #

   This section explains a few other things to watch for when porting
   Oracle PL/SQL functions to PostgreSQL.

41.13.2.1. Implicit Rollback after Exceptions #

   In PL/pgSQL, when an exception is caught by an EXCEPTION clause, all
   database changes since the block's BEGIN are automatically rolled back.
   That is, the behavior is equivalent to what you'd get in Oracle with:
BEGIN
    SAVEPOINT s1;
    ... code here ...
EXCEPTION
    WHEN ... THEN
        ROLLBACK TO s1;
        ... code here ...
    WHEN ... THEN
        ROLLBACK TO s1;
        ... code here ...
END;

   If you are translating an Oracle procedure that uses SAVEPOINT and
   ROLLBACK TO in this style, your task is easy: just omit the SAVEPOINT
   and ROLLBACK TO. If you have a procedure that uses SAVEPOINT and
   ROLLBACK TO in a different way then some actual thought will be
   required.

41.13.2.2. EXECUTE #

   The PL/pgSQL version of EXECUTE works similarly to the PL/SQL version,
   but you have to remember to use quote_literal and quote_ident as
   described in Section 41.5.4. Constructs of the type EXECUTE 'SELECT *
   FROM $1'; will not work reliably unless you use these functions.

41.13.2.3. Optimizing PL/pgSQL Functions #

   PostgreSQL gives you two function creation modifiers to optimize
   execution: “volatility” (whether the function always returns the same
   result when given the same arguments) and “strictness” (whether the
   function returns null if any argument is null). Consult the CREATE
   FUNCTION reference page for details.

   When making use of these optimization attributes, your CREATE FUNCTION
   statement might look something like this:
CREATE FUNCTION foo(...) RETURNS integer AS $$
...
$$ LANGUAGE plpgsql STRICT IMMUTABLE;

41.13.3. Appendix #

   This section contains the code for a set of Oracle-compatible instr
   functions that you can use to simplify your porting efforts.
--
-- instr functions that mimic Oracle's counterpart
-- Syntax: instr(string1, string2 [, n [, m]])
-- where [] denotes optional parameters.
--
-- Search string1, beginning at the nth character, for the mth occurrence
-- of string2.  If n is negative, search backwards, starting at the abs(n)'th
-- character from the end of string1.
-- If n is not passed, assume 1 (search starts at first character).
-- If m is not passed, assume 1 (find first occurrence).
-- Returns starting index of string2 in string1, or 0 if string2 is not found.
--

CREATE FUNCTION instr(varchar, varchar) RETURNS integer AS $$
BEGIN
    RETURN instr($1, $2, 1);
END;
$$ LANGUAGE plpgsql STRICT IMMUTABLE;


CREATE FUNCTION instr(string varchar, string_to_search_for varchar,
                      beg_index integer)
RETURNS integer AS $$
DECLARE
    pos integer NOT NULL DEFAULT 0;
    temp_str varchar;
    beg integer;
    length integer;
    ss_length integer;
BEGIN
    IF beg_index > 0 THEN
        temp_str := substring(string FROM beg_index);
        pos := position(string_to_search_for IN temp_str);

        IF pos = 0 THEN
            RETURN 0;
        ELSE
            RETURN pos + beg_index - 1;
        END IF;
    ELSIF beg_index < 0 THEN
        ss_length := char_length(string_to_search_for);
        length := char_length(string);
        beg := length + 1 + beg_index;

        WHILE beg > 0 LOOP
            temp_str := substring(string FROM beg FOR ss_length);
            IF string_to_search_for = temp_str THEN
                RETURN beg;
            END IF;

            beg := beg - 1;
        END LOOP;

        RETURN 0;
    ELSE
        RETURN 0;
    END IF;
END;
$$ LANGUAGE plpgsql STRICT IMMUTABLE;


CREATE FUNCTION instr(string varchar, string_to_search_for varchar,
                      beg_index integer, occur_index integer)
RETURNS integer AS $$
DECLARE
    pos integer NOT NULL DEFAULT 0;
    occur_number integer NOT NULL DEFAULT 0;
    temp_str varchar;
    beg integer;
    i integer;
    length integer;
    ss_length integer;
BEGIN
    IF occur_index <= 0 THEN
        RAISE 'argument ''%'' is out of range', occur_index
          USING ERRCODE = '22003';
    END IF;

    IF beg_index > 0 THEN
        beg := beg_index - 1;
        FOR i IN 1..occur_index LOOP
            temp_str := substring(string FROM beg + 1);
            pos := position(string_to_search_for IN temp_str);
            IF pos = 0 THEN
                RETURN 0;
            END IF;
            beg := beg + pos;
        END LOOP;

        RETURN beg;
    ELSIF beg_index < 0 THEN
        ss_length := char_length(string_to_search_for);
        length := char_length(string);
        beg := length + 1 + beg_index;

        WHILE beg > 0 LOOP
            temp_str := substring(string FROM beg FOR ss_length);
            IF string_to_search_for = temp_str THEN
                occur_number := occur_number + 1;
                IF occur_number = occur_index THEN
                    RETURN beg;
                END IF;
            END IF;

            beg := beg - 1;
        END LOOP;

        RETURN 0;
    ELSE
        RETURN 0;
    END IF;
END;
$$ LANGUAGE plpgsql STRICT IMMUTABLE;