Question

I want to extract text from a column using regular expressions in Oracle 11g. I have 2 queries that do the job but I’m looking for a (cleaner/nicer) way to do it. Maybe combining the queries into one or a new equivalent query. Here they are:

Query 1: identify rows that match a pattern:

select column1 from table1 where regexp_like(column1, pattern);

Query 2: extract all matched text from a matching row.

select regexp_substr(matching_row, pattern, 1, level) 
from dual
connect by level < regexp_count(matching_row, pattern);

I use PL/SQL to glue these 2 queries together, but it’s messy and clumsy. How can I combine them into 1 query. Thank you.

UPDATE: sample data for pattern ‘BC’:

row 1: ABCD
row 2: BCFBC
row 3: HIJ
row 4: GBC

Expected result is a table of 4 rows of ‘BC’.

Answer 1

You can also do it in one query, functions/procedures/packages not required:

WITH t1 AS (
SELECT 'ABCD' c1 FROM dual
UNION
SELECT 'BCFBC' FROM dual
UNION
SELECT 'HIJ' FROM dual
UNION
SELECT 'GBC' FROM dual
)
SELECT c1, regexp_substr(c1, 'BC', 1, d.l, 'i') thePattern, d.l occurrence
  FROM t1 CROSS JOIN (SELECT LEVEL l FROM dual CONNECT BY LEVEL < 200) d
WHERE regexp_like(c1,'BC','i')
   AND d.l <= regexp_count(c1,'BC');

C1    THEPATTERN           OCCURRENCE
----- -------------------- ----------
ABCD  BC                            1
BCFBC BC                            1
BCFBC BC                            2
GBC   BC                            1

SQL>

I’ve arbitrarily limited the number of occurrences to search for at 200, YMMV.