Try

SELECT tow.* FROM tow
	INNER JOIN inhistory ih ON tow.child_id = ih.child_id 
	WHERE tow.towid > 0 AND tow.vehi_id > 0 AND canccode = '    '
			AND 
                (ih.child_id IN ('<<lcchild_id>>', '<<lcParent_Id>>')
		 OR ih.parent_id IN ('<<lcchild_id>>', '<<lcParent_Id>>'))

>On systems with hundreds of thousands of records, these two queries take 17 seconds. Can anyone see a way to optimize them without changing the results? It's a strange query which was modified in the past to add the >0 section because sqlserver was returning errors without out it.
>
>

lcParent_Id = ALLTRIM(NVL(parent_id,''))  && 
>lcChild_Id = ALLTRIM(NVL(child_id,''))
>
>TEXT TO lcSQL NOSHOW PRETEXT 15 TEXTMERGE
>
>      SELECT tw.* FROM tow AS tw
>
>       INNER JOIN
>
>            (SELECT inhistory.child_id FROM inhistory
>
>             WHERE  inhistory.child_id = '<<lcchild_id>>'
>
>             OR inhistory.parent_id = '<<lcchild_id>>'
>
>             OR (LEN(inhistory.child_id)>0 AND inhistory.child_id = '<<lcParent_Id>>')
>
>             OR (LEN(inhistory.parent_id)>0 AND inhistory.parent_id = '<<lcParent_Id>>')) qry1
>
>      ON tw.child_id = qry1.child_id WHERE tw.towid > 0 AND tw.vehi_id > 0 AND canccode='    '
>
>ENDTEXT
>
>IF SQLProc("SP",m.lcSQL,,,"cTowCT") > 0 && Return any Tow records
>
>      TEXT TO lcSQL2 NOSHOW PRETEXT 15 TEXTMERGE
>
>            SELECT qry2.towid, vh.* FROM vhtable as vh 
>
>      INNER JOIN
>
>            (<<m.lcSQL>>) qry2
>
>            ON vh.vehi_id = qry2.vehi_id ORDER BY vh.vehi_id
>
>      ENDTEXT
>
>      IF SQLProc("SP",m.lcSQL2,,,"cvhtableIn") > 0 && Return the vhtable Records
>
>            SELECT cvhtableIn
>
>      ENDIF
>
>ENDIF