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check_agglevels_and_constraints() asserted that if we find an aggregate function in an EXPR_KIND_FROM_SUBSELECT expression, the expression must be in a LATERAL subquery. Alexander Lakhin found a case where that's not so: because of the odd scoping rules for NEW/OLD within a rule, a reference to NEW/OLD could cause an aggregate to be considered top-level even though it's in an unmarked sub-select. The error message that would be thrown seems sufficiently on-point, so just remove the Assert. (Hence, this is not a bug for production builds.) This Assert was added by me in commiteaccfded9(9.3 era). It looks like I put it in to cross-check that the new logic for detecting misplaced aggregates (using agglevelsup) caught the same cases that a previous check on p_lateral_active did. So there might have been some related misbehavior beforeeaccfded9... but that's very ancient history by now, so I didn't dig any deeper. Per bug #18608 from Alexander Lakhin. Back-patch to all supported branches. Discussion: https://postgr.es/m/18608-48de0717508ee429@postgresql.org
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_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) 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.