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I think when I added this assertion (in commit 8f889b108), I was only
thinking of the use of transformExpressionList at top level of INSERT
and VALUES. But it's also called by transformRowExpr(), which can
certainly occur in an UPDATE targetlist, so it's inappropriate to
suppose that p_multiassign_exprs must be empty. Besides, since the
input is not expected to contain ResTargets, there's no reason it
should contain MultiAssignRefs either. Hence this code need not
be concerned about the state of p_multiassign_exprs, and we should
just drop the assertion.
Per bug #17236 from ocean_li_996. It's been wrong for years,
so back-patch to all supported branches.
Discussion: https://postgr.es/m/17236-3210de9bcba1d7ca@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.