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transformTableLikeClause believed that it could process extended statistics immediately because "the representation of CreateStatsStmt doesn't depend on column numbers". That was true when extended stats were first introduced, but it was falsified by the addition of extended stats on expressions: the parsed expression tree is fed forward by the LIKE option, and that will contain Vars. So if the new table doesn't have attnums identical to the old one's (typically because there are some dropped columns in the old one), that doesn't work. The CREATE goes through, but it emits invalid statistics objects that will cause problems later. Fortunately, we already have logic that can adapt expression trees to the possibly-new column numbering. To use it, we have to delay processing of CREATE_TABLE_LIKE_STATISTICS into expandTableLikeClause, just as for other LIKE options that involve expressions. Per bug #18468 from Alexander Lakhin. Back-patch to v14 where extended statistics on expressions were added. Discussion: https://postgr.es/m/18468-f5add190e3fa5902@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.