Return all Groups for Outer Join + Count + Group By

Question

I have two tables, TC and XEA. The relationship is one TC to many XEA. TC is a lookup table and has one field, the code field TCSI_CD. XEA has the same code field called BAM_TCSI, which is the joining key, and also another field, the date field, LOAD_DATE.
I want to generate a report counting the records in XEA and grouping by the code list in TC. When a TC code is not found in XEA, the report must show a count of zero. The SQL shown does not work, as codes not found in XEA are omitted. Thanks in advance for any help.
SELECT
TC.TCSI_CD,DECODE(COUNT(XEA.BAM_TCSI),NULL,0,COUNT(XEA.BAM_TCSI))
FROM
OB_TCSI_CD TC,
TEMP_OB_XEA_HIST XEA
WHERE
TC.TCSI_CD = XEA.BAM_TCSI(+) AND
XEA.LOAD_DATE > '1-JUN-2002'
GROUP BY
TC.TCSI_CD

Answer 1

You need to include a (+) after the load_date column. If you omit that, it negates the whole outer join and turns your query into an inner join. Then just a regular count will work, returning 0 for the null values. You also might want to use the to_date function, instead of relying on your session having the matching nls_date_format.
SELECT   tc.tcsi_cd,
         COUNT (xea.bam_tcsi)
FROM     ob_tcsi_cd       tc,
         temp_ob_xea_hist xea
WHERE    tc.tcsi_cd = xea.bam_tcsi (+)
AND      xea.load_date (+) > TO_DATE ('1-JUN-2002', 'DD-MON-YYYY')
GROUP BY tc.tcsi_cd