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Tom Lane
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These were labeled with precedences just to avoid attaching explicit precedences to the productions in which they were the last terminal symbol. Since a terminal symbol precedence marking can affect many other things too, it seems like better practice to attach precedence labels to the productions, and not mark the terminal symbols. Ideally we'd also remove the precedence attached to NULL_P, but it turns out that we are actually depending on that having a precedence higher than POSTFIXOP, else we get a shift/reduce conflict for postfix operators in b_expr. (Which more or less proves my point about these markings having a high risk of unexpected consequences.) For the moment, move NULL_P into the set of keywords grouped with IDENT, so that at least it will act similarly to non-keywords; and document the interaction.
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 kwlookup.c turn keywords into specific tokens keywords.c table of standard keywords (passed to kwlookup.c) 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_func.c handle functions, table.column and column identifiers 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)