a4d75c86bf
Allow defining extended statistics on expressions, not just just on simple column references. With this commit, expressions are supported by all existing extended statistics kinds, improving the same types of estimates. A simple example may look like this: CREATE TABLE t (a int); CREATE STATISTICS s ON mod(a,10), mod(a,20) FROM t; ANALYZE t; The collected statistics are useful e.g. to estimate queries with those expressions in WHERE or GROUP BY clauses: SELECT * FROM t WHERE mod(a,10) = 0 AND mod(a,20) = 0; SELECT 1 FROM t GROUP BY mod(a,10), mod(a,20); This introduces new internal statistics kind 'e' (expressions) which is built automatically when the statistics object definition includes any expressions. This represents single-expression statistics, as if there was an expression index (but without the index maintenance overhead). The statistics is stored in pg_statistics_ext_data as an array of composite types, which is possible thanks to 79f6a942bd. CREATE STATISTICS allows building statistics on a single expression, in which case in which case it's not possible to specify statistics kinds. A new system view pg_stats_ext_exprs can be used to display expression statistics, similarly to pg_stats and pg_stats_ext views. ALTER TABLE ... ALTER COLUMN ... TYPE now treats indexes the same way it treats indexes, i.e. it drops and recreates the statistics. This means all statistics are reset, and we no longer try to preserve at least the functional dependencies. This should not be a major issue in practice, as the functional dependencies actually rely on per-column statistics, which were always reset anyway. Author: Tomas Vondra Reviewed-by: Justin Pryzby, Dean Rasheed, Zhihong Yu Discussion: https://postgr.es/m/ad7891d2-e90c-b446-9fe2-7419143847d7%40enterprisedb.com
44 lines
1.6 KiB
C
44 lines
1.6 KiB
C
/*-------------------------------------------------------------------------
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*
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* parse_utilcmd.h
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* parse analysis for utility commands
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*
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*
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* Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/parser/parse_utilcmd.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef PARSE_UTILCMD_H
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#define PARSE_UTILCMD_H
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#include "parser/parse_node.h"
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struct AttrMap; /* avoid including attmap.h here */
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extern List *transformCreateStmt(CreateStmt *stmt, const char *queryString);
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extern AlterTableStmt *transformAlterTableStmt(Oid relid, AlterTableStmt *stmt,
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const char *queryString,
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List **beforeStmts,
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List **afterStmts);
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extern IndexStmt *transformIndexStmt(Oid relid, IndexStmt *stmt,
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const char *queryString);
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extern CreateStatsStmt *transformStatsStmt(Oid relid, CreateStatsStmt *stmt,
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const char *queryString);
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extern void transformRuleStmt(RuleStmt *stmt, const char *queryString,
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List **actions, Node **whereClause);
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extern List *transformCreateSchemaStmt(CreateSchemaStmt *stmt);
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extern PartitionBoundSpec *transformPartitionBound(ParseState *pstate, Relation parent,
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PartitionBoundSpec *spec);
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extern List *expandTableLikeClause(RangeVar *heapRel,
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TableLikeClause *table_like_clause);
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extern IndexStmt *generateClonedIndexStmt(RangeVar *heapRel,
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Relation source_idx,
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const struct AttrMap *attmap,
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Oid *constraintOid);
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#endif /* PARSE_UTILCMD_H */
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