casey 9a72c28832 Add DECODE builtin ...

This adds DECODE functionality into the existing CaseExpr class. There
will be no separate backend impementation for DECODE, it will be sent to
the backend as a CASE expr so the existing codegen function can be used.

Because Oracle does cast checking during execution and Impala cast
checking during analysis, some uses of DECODE that are valid in Oracle
are invalid in Impala.

Ex:

  SELECT DECODE(foo, bar, int_col, baz, string_col_containing_only_ints)
  FROM ...

  would be run on Oracle. If string_col_containing_only_ints actually
  contained non-INTs, an error would be thrown during execution and no
  results would be returned. In Impala an error is thrown during analysis.
  If a CAST was added to the STRING column, a cast failure would result in
  NULL.

Change-Id: Ia08cc2389abb6f843bba117e7091c659ad25ff41
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/4334
Tested-by: jenkins
Reviewed-by: Casey Ching <casey@cloudera.com>
Tested-by: Casey Ching <casey@cloudera.com>

2014-09-26 12:26:46 -07:00

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