pgsql: Suggest to the user the column they may have meant to reference.

Suggest to the user the column they may have meant to reference.

Error messages informing the user that no such column exists can
sometimes provoke a perplexed response.  This often happens due to
a subtle typo in the column name or, perhaps less likely, in the
alias name.  To speed discovery of what the real issue is in such
cases, we'll now search the range table for approximate matches.
If there are one or two such matches that are good enough to think
that they might be what the user intended to type, and better than
all other approximate matches, we'll issue a hint suggesting that
the user might have intended to reference those columns.

Peter Geoghegan and Robert Haas

Branch
------
master

Details
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http://git.postgresql.org/pg/commitdiff/e529cd4ffa605c6f14f1391af5559b3a44da0336

Modified Files
--------------
src/backend/parser/parse_expr.c           |    9 +-
src/backend/parser/parse_func.c           |    2 +-
src/backend/parser/parse_relation.c       |  266 +++++++++++++++++++++++++----
src/backend/utils/adt/levenshtein.c       |    9 +
src/include/parser/parse_relation.h       |   21 ++-
src/test/regress/expected/alter_table.out |    3 +
src/test/regress/expected/join.out        |   38 +++++
src/test/regress/sql/join.sql             |   24 +++
8 files changed, 334 insertions(+), 38 deletions(-)