Replace REGEXP_SUBSTR in SQL Server

SQL Fiddle

MS SQL Server 2014 Schema Setup:

CREATE TABLE table_name ( name VARCHAR(50) );
INSERT INTO table_name
SELECT 'AE 344592001H 6186694' UNION ALL
SELECT 'AE_161038002_6044777' UNION ALL
SELECT 'BC_VIVS_HNB011A_1WAM' UNION ALL
SELECT 'BC_56230A_30SP' UNION ALL
SELECT 'CG_3334902_NETWK_ ACTLM_3334912' UNION ALL
SELECT 'CG_3334574_HMO1_CORACT_3334575' UNION ALL
SELECT 'CG_3207160_POSC_1502AH_3207161' UNION ALL
SELECT 'UH_141015_RHM' UNION ALL
SELECT 'UH_127757_RIV' UNION ALL
SELECT 'UH 523725 RIV' UNION ALL
SELECT 'BS_W0055785_C500_M0005672';

Query 1:

WITH Names ( lvl, name, remaining, idx ) AS (
  SELECT 1,
         name,
         name,
         CHARINDEX( '_', name )
  FROM   table_name
  UNION ALL
  SELECT lvl+1,
         name,
         SUBSTRING(remaining,idx+1,LEN(remaining)-idx),
         CASE WHEN CHARINDEX( '_', remaining, idx+1 ) = 0
              THEN 0
              ELSE CHARINDEX( '_', remaining, idx+1 ) - idx
              END
  FROM   Names
  WHERE  idx > 0
)
SELECT Name,
       MAX( CASE WHEN lvl = 3 AND ( Name LIKE 'CG%' OR idx = 0 ) THEN remaining
                 WHEN lvl = 3 THEN SUBSTRING( remaining, 1, idx - 1 )
                 END ) AS OPT,
       MAX( CASE WHEN lvl = 2 AND ( Name LIKE 'CG%' OR idx = 0 ) THEN remaining
                 WHEN lvl = 2 THEN SUBSTRING( remaining, 1, idx - 1 )
                 END ) AS Name2
FROM   Names
GROUP BY Name

Results:

|                            Name |                  OPT |                        Name2 |
|---------------------------------|----------------------|------------------------------|
|           AE 344592001H 6186694 |               (null) |                       (null) |
|            AE_161038002_6044777 |              6044777 |                    161038002 |
|                  BC_56230A_30SP |                 30SP |                       56230A |
|            BC_VIVS_HNB011A_1WAM |              HNB011A |                         VIVS |
|       BS_W0055785_C500_M0005672 |                 C500 |                     W0055785 |
|  CG_3207160_POSC_1502AH_3207161 |  POSC_1502AH_3207161 |  3207160_POSC_1502AH_3207161 |
|  CG_3334574_HMO1_CORACT_3334575 |  HMO1_CORACT_3334575 |  3334574_HMO1_CORACT_3334575 |
| CG_3334902_NETWK_ ACTLM_3334912 | NETWK_ ACTLM_3334912 | 3334902_NETWK_ ACTLM_3334912 |
|                   UH 523725 RIV |               (null) |                       (null) |
|                   UH_127757_RIV |                  RIV |                       127757 |
|                   UH_141015_RHM |                  RHM |                       141015 |

Query 2:

CHARINDEX( expressionToFind, expressionToSerach[, startIndex] ) can be used to find the instances of _ in the word.

• CHARINDEX( '_', name ) will find the index of the first instance of an _.
• CHARINDEX( '_', name, CHARINDEX( '_', name ) + 1 ) will find the index of the second instance of an _ or will return 0 if there are not two _ characters.
• CHARINDEX( '_', name, CHARINDEX( '_', name, CHARINDEX( '_', name ) + 1 ) + 1) will find the index of the third instance of an _ or will return 0 if there are not three _ characters.

Nesting this into an inner select you can use it to get the appropriate SUBSTRINGs in an outer select like this:

SELECT name,
       CASE WHEN idx2 > idx1 AND ( Name LIKE 'CG%' OR idx3 = 0 )THEN SUBSTRING( name, idx2 + 1, LEN( name ) )
            WHEN idx3 > idx2 THEN SUBSTRING( name, idx2 + 1, idx3 - idx2 - 1 )
            END AS OPT,
       CASE WHEN name LIKE 'CG%' THEN SUBSTRING( name, idx1 + 1, LEN( name ) )
            WHEN idx2 > idx1 THEN SUBSTRING( name, idx1 + 1, idx2 - idx1 - 1 )
            END AS Name2
FROM   (
  SELECT name,
         CHARINDEX( '_', name ) AS idx1,
         CHARINDEX( '_', name, CHARINDEX( '_', name ) + 1 ) AS idx2,
         CHARINDEX( '_', name, CHARINDEX( '_', name, CHARINDEX( '_', name ) + 1 ) + 1 ) AS idx3
  FROM   table_name
) t

Results:

|                            name |                  OPT |                        Name2 |
|---------------------------------|----------------------|------------------------------|
|           AE 344592001H 6186694 |               (null) |                       (null) |
|            AE_161038002_6044777 |              6044777 |                    161038002 |
|            BC_VIVS_HNB011A_1WAM |              HNB011A |                         VIVS |
|                  BC_56230A_30SP |                 30SP |                       56230A |
| CG_3334902_NETWK_ ACTLM_3334912 | NETWK_ ACTLM_3334912 | 3334902_NETWK_ ACTLM_3334912 |
|  CG_3334574_HMO1_CORACT_3334575 |  HMO1_CORACT_3334575 |  3334574_HMO1_CORACT_3334575 |
|  CG_3207160_POSC_1502AH_3207161 |  POSC_1502AH_3207161 |  3207160_POSC_1502AH_3207161 |
|                   UH_141015_RHM |                  RHM |                       141015 |
|                   UH_127757_RIV |                  RIV |                       127757 |
|                   UH 523725 RIV |               (null) |                       (null) |
|       BS_W0055785_C500_M0005672 |                 C500 |                     W0055785 |