Thanks to Lynn & Sean for the formatted query:

-- code rewrites are iterative in nature. You make a change or two,

-- test thoroughly, amend if necessary, then make another change.

-- Here's two changes (with no data to test against):

-- 1: use of table aliases and USE to eliminate unnecessary characters

-- and 2: a rewrite of the subquery in the WHERE clause.

USE [Build1]

SELECT DISTINCT TYPE_ID

INTO #TypeIDNoChild

FROM TBL_TYPE_DEF

WHERE TYPE_ID NOT IN (SELECT CHILD_TYPE FROM TBL_RELATIONSHIPS_ALLOWED)

SELECT

td.TYPE_NAME

,i.DOC_NAME

,i.DOC

,i.SEC

,i.VER

,r.JUSTIFICATION

FROM TBL_INSTANCES i

INNER JOIN TBL_TYPE_DEF td

ON i.TYPE_ID = td.TYPE_ID

LEFT JOIN TBL_RELATIONSHIPS r

ON i.DOC = r.PARENT_DOC

AND i.SEC = r.PARENT_SEC

AND i.VER = r.PARENT_VER

WHERE NOT EXISTS (

SELECT 1

FROM TBL_RELATIONSHIPS ri

INNER JOIN TBL_INSTANCES ii

ON ii.DOC = ri.PARENT_DOC

AND ii.SEC = ri.PARENT_SEC

AND ii.VER = ri.PARENT_VER -- nullable

AND ii.TYPE_ID IN (SELECT TYPE_ID FROM #TypeIDNoChild)

WHERE ri.CHILD_DOC IS NOT NULL

AND ri.PARENT_DOC = i.DOC

AND ri.PARENT_SEC = i.SEC

AND ri.PARENT_VER = i.VER

)

AND i.TYPE_ID IN (SELECT TYPE_ID FROM #TypeIDNoChild)

ORDER BY td.TYPE_ID

,i.DOC

,i.SEC

,i.VER