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GROUP BY ALL is a form of GROUP BY that adds any TargetExpr that does not contain an aggregate or window function into the groupClause of the query, making it exactly equivalent to specifying those same expressions in an explicit GROUP BY list. This feature is useful for certain kinds of data exploration. It's already present in some other DBMSes, and the SQL committee recently accepted it into the standard, so we can be reasonably confident in the syntax being stable. We do have to invent part of the semantics, as the standard doesn't allow for expressions in GROUP BY, so they haven't specified what to do with window functions. We assume that those should be treated like aggregates, i.e., left out of the constructed GROUP BY list. In passing, wordsmith some existing documentation about GROUP BY, and update some neglected synopsis entries in select_into.sgml. Author: David Christensen <david@pgguru.net> Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us> Discussion: https://postgr.es/m/CAHM0NXjz0kDwtzoe-fnHAqPB1qA8_VJN0XAmCgUZ+iPnvP5LbA@mail.gmail.com
src/backend/parser/README Parser ====== This directory does more than tokenize and parse SQL queries. It also creates Query structures for the various complex queries that are passed to the optimizer and then executor. parser.c things start here scan.l break query into tokens scansup.c handle escapes in input strings gram.y parse the tokens and produce a "raw" parse tree analyze.c top level of parse analysis for optimizable queries parse_agg.c handle aggregates, like SUM(col1), AVG(col2), ... parse_clause.c handle clauses like WHERE, ORDER BY, GROUP BY, ... parse_coerce.c handle coercing expressions to different data types parse_collate.c assign collation information in completed expressions parse_cte.c handle Common Table Expressions (WITH clauses) parse_expr.c handle expressions like col, col + 3, x = 3 or x = 4 parse_enr.c handle ephemeral named rels (trigger transition tables, ...) parse_func.c handle functions, table.column and column identifiers parse_jsontable.c handle JSON_TABLE parse_merge.c handle MERGE parse_node.c create nodes for various structures parse_oper.c handle operators in expressions parse_param.c handle Params (for the cases used in the core backend) parse_relation.c support routines for tables and column handling parse_target.c handle the result list of the query parse_type.c support routines for data type handling parse_utilcmd.c parse analysis for utility commands (done at execution time) See also src/common/keywords.c, which contains the table of standard keywords and the keyword lookup function. We separated that out because various frontend code wants to use it too.