Reverse String Word by Word using SQL

Question

I would need to reverse the word positions in a sentence or String.

For example : \"Hello World! I Love StackOverflow\", to be displayed as \"StackOverflow          


        

Answer 1

XML-based version to avoid defining your own function; requires 11g for listagg():

select listagg(word, ' ') within group (order by rn desc) as reversed
from (
  select word, rownum as rn
  from xmltable('for $i in ora:tokenize($STR, " ") return $i'
    passing 'Hello World! I Love StackOverflow' as str
    columns word varchar2(4000) path '.'
  )
);

REVERSED                               
----------------------------------------
StackOverflow Love I World! Hello        

The XMLTable() does the tokenising, and assigns a row number:

select rownum as rn, word
from xmltable('for $i in ora:tokenize($STR, " ") return $i'
  passing 'Hello World! I Love StackOverflow' as str
  columns word varchar2(4000) path '.'
);

        RN WORD               
---------- --------------------
         1 Hello                
         2 World!               
         3 I                    
         4 Love                 
         5 StackOverflow        

The listagg() then pieces it back together in reverse order.

Answer 2

Create a Function:

REGEXP_SUBSTR('Your text here','[^ ]+', 1, ?) will extract a word from the text using Space as a delimiter. Tt returns the original String itself on Exception!

CREATE OR REPLACE FUNCTION reverse_words (v_STRING IN VARCHAR2)
RETURN VARCHAR2
IS
   L_TEMP_TEXT  VARCHAR2(4000);
   L_FINAL_TEXT  VARCHAR2(4000);
   V_LOOPCOUNT NUMBER :=0;
   T_WORD VARCHAR2(4000);
BEGIN
      L_TEMP_TEXT := regexp_replace(V_STRING,'[[:space:]]+',' '); -- Replace multiple spaces as single
      LOOP
        v_LOOPCOUNT := v_LOOPCOUNT+1;
        T_WORD      := REGEXP_SUBSTR(L_TEMP_TEXT,'[^ ]+', 1, V_LOOPCOUNT);
        L_final_TEXT := T_WORD||' '||L_final_TEXT;
      EXIT WHEN T_WORD IS NULL;
      END LOOP;
   RETURN(TRIM(L_final_TEXT));
EXCEPTION
    WHEN OTHERS THEN
        DBMS_OUTPUT.PUT_LINE(sqlerrm||chr(10)||dbms_utility.format_error_backtrace);
        RETURN V_STRING;
END reverse_words;
/

Sample Result:

You can call reverse_words(yourcolumn) from your_table

SQL> select reverse_words('Hello World! I Love StackOverflow') "Reversed" from dual;

Reversed
--------------------------------------------------------------------------------
StackOverflow Love I World! Hello

Answer 3

Here you go:

WITH sel_string AS 
      (SELECT 'Hello World! I Love StackOverflow' AS fullstring FROM DUAL)
  SELECT SUBSTR(fullstring, beg + 1, end_p - beg - 1) AS token
    FROM (SELECT beg, LEAD(beg) OVER (ORDER BY beg) AS end_p, fullstring
            FROM (SELECT beg, fullstring
                    FROM (SELECT LEVEL beg, fullstring
                            FROM sel_string
                            CONNECT BY LEVEL <= LENGTH(fullstring))
                    WHERE INSTR(' ', SUBSTR(fullstring, beg, 1)) > 0
                  UNION ALL
                    SELECT 0, fullstring FROM sel_string
                  UNION ALL
                    SELECT LENGTH(fullstring) + 1, fullstring FROM sel_string))
    WHERE end_p IS NOT NULL AND
          end_p > beg + 1
    ORDER BY ROWNUM DESC;

All in one SQL query. I wish I could claim credit for this query but I can't - found it years ago on the net and have used it ever since.

Share and enjoy.

Answer 4

One more solution

WITH str_tab(str1, rn) AS
(SELECT regexp_substr(str, '[^\[:space:]]+', 1, LEVEL), 
        LEVEL 
   FROM (SELECT 'Hello World! I Love StackOverflow' str
           FROM dual) tab
CONNECT BY LEVEL <= LENGTH(str) - LENGTH(REPLACE(str, ' ')) + 1)
SELECT listagg(str1, ' ') WITHIN GROUP (ORDER BY rn DESC) AS new_text
  FROM str_tab;

Answer 5

DECLARE 

in_string VARCHAR2(500);
pros_string  VARCHAR2(500);
out_string  VARCHAR2(800);  
spce_cnt NUMBER;


BEGIN

in_string := 'Hello World! I Love StackOverflow';
pros_string := ' '||in_string||' ' ;   
spce_cnt := REGEXP_COUNT(pros_string,' ',1);
FOR i IN reverse  1.. spce_cnt-1  
LOOP                               
 out_string := out_string||' '|| SubStr (pros_string,InStr(pros_string, ' ',1,i)+1 ,InStr(SubStr (pros_string,InStr(pros_string, ' ',1,i)+1 ),' '  ));    
Dbms_Output.Put_Line(out_string);    
END LOOP; 
END;