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It is possible that a given record will not have any LC subject headings. In the screenshot below we see a typical example of subject headings in a record. The first 2 lines in the screenshot show two parts of a single subject heading: 650  0  $a Cultural property $x Protection (International law). The number 1 in the ord column tells us that these two subfields are the elements that make up the first subject heading in the record. The second subject heading has 3 separate elements, divided into three subfields:         650  0 ‡a Cultural property ‡x Protection ‡z Europe .
9:40
And and so on. There are 4 LC subject headings in this record, and numerous other subject terms as well.  To find the first subject term in a record, I recommend using that number 1 in the ord field.

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For example, to pull the first LOC subject heading from a bibliographic record using its instance hrid, you would use:

SELECT DISTINCT
    SM.instance_hrid,
    SM.field,
    SM.ind2,
    SM.ord,
    SM.sf,
    SM."content"
FROM
    public.srs_marctab SM
 WHERE SM.instance_hrid = '15309598'
 AND SM.field LIKE '6%%'
 AND SM.ord='1'
 AND SM.ind2='0'

;

Which results in:

Further, if you want to display the subject heading as it appears in the bibliographic record, you may use a STRING_AGG FUNCTION to format the content rows as a subject heading string. Here is an example using instance HRIDs between 6403921 and 6404000:

WITH lc as

(select distinct SELECT DISTINCT
        
sm.instance_hrid,
      
  sm.field,
      
  sm.content

FROM from srs_marctab sm  sm
where
WHERE sm.instance_hrid = between '6403921' and '153095986404000'
      
and  AND sm.field like '6%%'
        
andAND sm.sf in ('a','x','y','z')
        
andAND sm.ind2 = '0'
        andAND sm.ord = '1'
)

SELECT
 ) select       lc.instance_hrid,
        lc.field,
        string_agg (distinct lc.content, ' -- ') as lc_subject from

FROM lc

GROUP groupBY
 by        lc.instance_hrid,
        lc.field ;
;


And the results would be:

Image Added