ORA-00905: missing keyword error in case after where clause

Question

I have the following query which is giving error ORA-00905: missing keyword. I've not been able to find the syntax despite continuous efforts for last few hours. Please help.

SELECT a.DOCUMENT_CATEGORY,
         a.template_id,
         a.category_id,
         a.REVIEW_CATEGORY,
         a.WITH_BIDS,
         a.WITH_FINAL_DOCUMENTS,
         b.divn_id,
         b.deptt_id,
         a.vdr_id,
         C.DEPARTMENT,
         a.TEMPLATE_TITLE
    FROM DCTM_VDR_REF_DTLS a, DCTM_VDR_REF_MASTER b, VW_DIVN_DIR c
   WHERE     b.DIVN_ID = c.DIVN_CODE
         AND b.DEPTT_ID = c.SECTN_CODE
         AND a.vdr_id = b.vdr_id
         AND (b.REFERENCE_NUMBER, b.APPROVED_ON) IN
                (  SELECT MAX (REFERENCE_NUMBER), MAX (APPROVED_ON)
                     FROM DCTM_VDR_REF_MASTER
                    WHERE     REFERENCE_NUMBER =
                                 (SELECT DISTINCT
                                         NVL (TRIM (MR_NUMBER), TRIM (TENDER_NO))
                                    FROM EILEDMS.EIL_DOCUMENT_SV@EDMS_DBLINK
                                   WHERE     object_name =
                                                'A307-0IC-JA-MR-7960-1030-157-FOA'
                                         AND r_object_type =
                                                'eil_foa_order_pr_doc'
                                         AND (   title = 'FOA'
                                              OR title = 'DRAFT FOA'))
                          AND APPROVED_ON IS NOT NULL
                 GROUP BY DIVN_ID, DEPTT_ID)
         AND REVIEW_CATEGORY <> 'Delete Category'
         AND (CASE (SELECT IS_SCHEDULE_LOCKED
                      FROM DCTM_VENDOR_SCHEDULE
                     WHERE SCH_ID = 359)
                 WHEN 0
                 THEN
                    1
                 WHEN 1
                 THEN
                    (a.template_id || '-' || a.category_id) IN
                       (SELECT template_id || '-' || category_id
                          FROM DCTM_VENDOR_SCH_UNLOCK_DTLS
                         WHERE     APPROVAL = 'Y'
                               AND APPROVAL_UPTO >= SYSDATE
                               AND CONSUMED = 0
                               AND sch_ID = 359)
              END) = 1
ORDER BY c.DEPARTMENT ASC,
         a.TEMPLATE_ID,
         a.SORT_ORDER,
         a.DOCUMENT_CATEGORY ASC

Can't we use IN clause inside a THEN statement?

Answer 1

Now that you've edited your question, it looks like you are simply trying to look up category_id and template_id in DCTM_VENDOR_SCH_UNLOCK_DTLS. Does the following work for you?

then 
(
  SELECT COUNT(*) -- 1 if found, 0 otherwise
    FROM DCTM_VENDOR_SCH_UNLOCK_DTLS
   WHERE     APPROVAL = 'Y'
         AND APPROVAL_UPTO >= SYSDATE
         AND CONSUMED = 0
         AND sch_ID = 359
         AND template_id = a.template_id
         AND category_id = a.category_id
         AND rownum = 1
)

Answer 2

This is not actually about an IN clause after WHERE being allowed or not. The expression

a.category_id IN (SELECT ...)

evaluates to TRUE or FALSE. Your statement

a.template_id || '-' || a.category_id IN (SELECT ...)

tries to concatenate that TRUE or FALSE with a.template_id and a minus sign. This is not possible, as there is no boolean type in Oracle SQL. Think it over what you actually want to concatenate.

EDIT: Now that you set parentheses, you compare a string with another string resulting from a select statement. Fine so far. But still: All this evaluates to a boolean, not a number. Your first then results in a number (1), your second in a boolean (TRUE or FALSE). Oracle SQL has no boolean type, so your expression makes no sense to the parser and you get a syntax error.