GROUP BY CASE statement

Question

I have a working query that is grouping data by hardware model and a result  but the problem is there are many  results    I have tried to reduce that down to  if result   0  then keep as 0  else set it to 1    This generally works  but I end up having       day            name        type   case   count ------------ ---------------- ------ ------ -------  2013-11-06   modelA              1      0     972  2013-11-06   modelA              1      1      42  2013-11-06   modelA              1      1       2  2013-11-06   modelA              1      1      11  2013-11-06   modelB              1      0     456  2013-11-06   modelB              1      1      16  2013-11-06   modelB              1      1       8  2013-11-06   modelB              3      0   21518  2013-11-06   modelB              3      1       5  2013-11-06   modelB              3      1       7  2013-11-06   modelB              3      1     563   Instead of the aggregate I am trying to achieve  where only 1 row per type case combo       day            name        type   case   count ------------ ---------------- ------ ------ -------  2013-11-06   modelA              1      0     972  2013-11-06   modelA              1      1      55  2013-11-06   modelB              1      0     456  2013-11-06   modelB              1      1      24  2013-11-06   modelB              3      0   21518  2013-11-06   modelB              3      1     575   Here is my query   select CURRENT DATE-1 AS day  model name  attempt type          CASE WHEN attempt result   0 THEN 0 ELSE 1 END          count     from attempt attempt  prod hw id prod hw id  model model where time  gt    2013-11-06 00 00 00    AND time  lt   2013-11-07 00 00 00  AND attempt hard id   prod hw id hard id AND prod hw id model id   model model id group by model name  attempt type  attempt result order by model name  attempt type  attempt result    Any tips on how I can achieve this would be awesome   Day will always be defined in the WHERE clause  so it will not vary  name  type  result case  and count will vary  In short  for any given model I want only 1 row per  type   case  combo  As you can see in the first result set I have 3 rows for modelA that have type 1 and case 1  because there are many  result  values that I have turned into 0 0 and anything else 1   I want that to be represented as 1 row with the count aggregated as in example data set 2

User · Answer

Aliases can be used only if they were introduced in the preceding step. So aliases in the SELECT clause can be used in the ORDER BY but not the GROUP BY clause.

Reference: Microsoft T-SQL Documentation for further reading.

FROM
ON
JOIN
WHERE
GROUP BY
WITH CUBE or WITH ROLLUP
HAVING
SELECT
DISTINCT
ORDER BY
TOP

Hope this helps.

User · Answer

Try adding the other two non COUNT columns to the GROUP BY   select CURRENT DATE-1 AS day   model name   attempt type   CASE WHEN attempt result   0 THEN 0 ELSE 1 END   count     from attempt attempt  prod hw id prod hw id  model model where time  gt    2013-11-06 00 00 00    AND time  lt   2013-11-07 00 00 00  AND attempt hard id   prod hw id hard id AND prod hw id model id   model model id group by 1 2 3 4 order by model name  attempt type  attempt result

User · Answer

Your query would work already - except that you are running into naming conflicts or just confusing the output column  the CASE expression  with source column result  which has different content       GROUP BY model name  attempt type  attempt result      You need to GROUP BY your CASE expression instead of your source column       GROUP BY model name  attempt type          CASE WHEN attempt result   0 THEN 0 ELSE 1 END      Or provide a column alias that s different from any column name in the FROM list - or else that column takes precedence   SELECT            CASE WHEN attempt result   0 THEN 0 ELSE 1 END AS result1     GROUP BY model name  attempt type  result1      The SQL standard is rather peculiar in this respect  Quoting the manual here      An output column s name can be used to refer to the column s value in   ORDER BY and GROUP BY clauses  but not in the WHERE or HAVING clauses    there you must write out the expression instead    And      If an ORDER BY expression is a simple name that matches both an output   column name and an input column name  ORDER BY will interpret it as   the output column name  This is the opposite of the choice that GROUP BY    will make in the same situation  This inconsistency is made to be   compatible with the SQL standard    Bold emphasis mine   These conflicts can be avoided by using positional references  ordinal numbers  in GROUP BY and ORDER BY  referencing items in the SELECT list from left to right  See solution below  The drawback is  that this may be harder to read and vulnerable to edits in the SELECT list  one might forget to adapt positional references accordingly     But you do not have to add the  column day to the GROUP BY clause  as long as it holds a constant value  CURRENT DATE-1    Rewritten and simplified with proper JOIN syntax and positional references it could look like this   SELECT m name        a type        CASE WHEN a result   0 THEN 0 ELSE 1 END AS result        CURRENT DATE - 1 AS day        count    AS ct FROM   attempt    a JOIN   prod hw id p USING  hard id  JOIN   model      m USING  model id  WHERE  ts  gt    2013-11-06 00 00 00    AND    ts  lt    2013-11-07 00 00 00  GROUP  BY 1 2 3 ORDER  BY 1 2 3   Also note that I am avoiding the column name time  That s a reserved word and should never be used as identifier  Besides  your  time  obviously is a timestamp or date  so that is rather misleading

User · Answer

For TSQL I like to encapsulate case statements in an outer apply  This prevents me from having to have the case statement written twice  allows reference to the case statement by alias in future joins and avoids the need for positional references   select oa day   model name   attempt type   oa result COUNT    MyCount  FROM attempt attempt  prod hw id prod hw id  model model WHERE time  gt    2013-11-06 00 00 00    AND time  lt   2013-11-07 00 00 00  AND attempt hard id   prod hw id hard id AND prod hw id model id   model model id OUTER APPLY       SELECT CURRENT DATE-1 AS day       CASE WHEN attempt result   0 THEN 0 ELSE 1 END result       oa     group by oa day   model name   attempt type   oa result order by model name  attempt type  oa result

User · Answer

can you please try this  replace the case statement with the below one   Sum CASE WHEN attempt result   0 THEN 0 ELSE 1 END  as Count

[sql] GROUP BY + CASE statement

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