Oracle PL/SQL/Regular Expressions/Group

Group the letters "ir" together by putting them in parentheses

SQL> create table TestTable(
  2    ID                    VARCHAR2(4 BYTE)         NOT NULL,
  3    Description           VARCHAR2(30 BYTE)
  4  )
  5  /
Table created.
SQL>
SQL>
SQL> insert into TestTable (ID, Description) values("1","1234 5th Street");
1 row created.
SQL> insert into TestTable (ID, Description) values("2","1 Culloden Street");
1 row created.
SQL> insert into TestTable (ID, Description) values("3","1234 Road");
1 row created.
SQL> insert into TestTable (ID, Description) values("4","33 Thrid Road");
1 row created.
SQL> insert into TestTable (ID, Description) values("5","One than another");
1 row created.
SQL> insert into TestTable (ID, Description) values("6","2003 Movie");
1 row created.
SQL> insert into TestTable (ID, Description) values("7","Start With Letters");
1 row created.
SQL>
SQL> select * from TestTable;
ID   DESCRIPTION
---- ------------------------------
1    1234 5th Street
2    1 Culloden Street
3    1234 Road
4    33 Thrid Road
5    One than another
6    2003 Movie
7    Start With Letters
7 rows selected.
SQL>
SQL> --Group the letters "ir" together by putting them in parentheses and then parenthesizing the suffix using alternation:
SQL>
SQL> SELECT description, REGEXP_SUBSTR(description,"(ir)(d|s)") FROM testTable;
DESCRIPTION                    REGEXP_SUBSTR(DESCRIPTION,"(IR
------------------------------ ------------------------------
1234 5th Street
1 Culloden Street
1234 Road
33 Thrid Road
One than another
2003 Movie
Start With Letters
7 rows selected.
SQL>
SQL>
SQL>
SQL> drop table TestTable;
Table dropped.
SQL>
SQL>

Parenthesize both expressions

SQL> create table TestTable(
  2    ID                    VARCHAR2(4 BYTE)         NOT NULL,
  3    Description           VARCHAR2(30 BYTE)
  4  )
  5  /
Table created.
SQL>
SQL>
SQL> insert into TestTable (ID, Description) values("1","1234 5th Street");
1 row created.
SQL> insert into TestTable (ID, Description) values("2","1 Culloden Street");
1 row created.
SQL> insert into TestTable (ID, Description) values("3","1234 Road");
1 row created.
SQL> insert into TestTable (ID, Description) values("4","33 Thrid Road");
1 row created.
SQL> insert into TestTable (ID, Description) values("5","One than another");
1 row created.
SQL> insert into TestTable (ID, Description) values("6","2003 Movie");
1 row created.
SQL> insert into TestTable (ID, Description) values("7","Start With Letters");
1 row created.
SQL>
SQL> select * from TestTable;
ID   DESCRIPTION
---- ------------------------------
1    1234 5th Street
2    1 Culloden Street
3    1234 Road
4    33 Thrid Road
5    One than another
6    2003 Movie
7    Start With Letters
7 rows selected.
SQL>
SQL>
SQL>
SQL> -- Parenthesize both expressions
SQL>
SQL> SELECT description, REGEXP_SUBSTR(description,"(ir)d|s") FROM testTable;
DESCRIPTION                    REGEXP_SUBSTR(DESCRIPTION,"(IR
------------------------------ ------------------------------
1234 5th Street
1 Culloden Street
1234 Road
33 Thrid Road
One than another
2003 Movie
Start With Letters             s
7 rows selected.
SQL>
SQL>
SQL> drop table TestTable;
Table dropped.
SQL>
SQL>
SQL>

REGEXP_SUBSTR("Yababa dababa do","(ab)")

SQL> --Backreference
SQL>
SQL>
SQL> SELECT REGEXP_SUBSTR("Yababa dababa do","(ab)") FROM dual;
RE
--
ab
SQL>

REGEXP_SUBSTR("Yababa dababa do","(ab)\1"), backreference option

SQL> --pattern is matched. If we use the backreference option, the query looks like this:
SQL>
SQL> SELECT REGEXP_SUBSTR("Yababa dababa do","(ab)\1")FROM dual;
REGE
----
abab
SQL>

Using backreference: REGEXP_REPLACE("H1234 H4321 H2345","(.*) (.*) (.*)","\3, \2 \1")

SQL> --For a better example of using backreference, let"s suppose we wanted to convert a 
name in the form "first middle last" into the "last, middle first" format. Consider this command:
SQL>
SQL> SELECT REGEXP_REPLACE("H1234 H4321 H2345","(.*) (.*) (.*)","\3, \2 \1")FROM dual;
REGEXP_REPLACE("H1
------------------
H2345, H4321 H1234
SQL>
SQL>