--# 覆盖索引 - idx_idinfo_indext create index idx_idinfo_indext on index_t(id) include(info) ; -- 再次查看执行计划 maleah_db=# explain (analyze on,verbose on) select info from index_t where id = 500 ; QUERY PLAN --- Index Only Scan using idx_idinfo_indext on public.index_t...
针对某个具体的表上索引,PG 提供了pg_index_column_has_property()等函数来查询索引相关的性质。 对于索引 AM,如果想被不同类型真正地使用,它还必须拥有一个或者多个相应的 opfamily (操作符族)和 opclass (操作符类),这些项的元信息记录在 pg_opfamily,pg_opclass,pg_amop 和pg_amproc 系统表中,被用于...
CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ] name ] ON [ ONLY ] table_name [ USING method ] ( { column_name | ( expression ) } [ COLLATE collation ] [ opclass [ ( opclass_parameter = value [, ... ] ) ] ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ...
Creating a multicolumn index in PostgreSQL is a common practice when we want to create an index on multiple columns. 在PostgreSQL 中创建多列索引是一种常见的做法,因为我们要在多列上创建索引。 PostgreSQL Index Types The PostgreSQL index facilitates the efficient retrieval of data from the table. Th...
in a multi-column index, a key tuple contains the pair (column number, key datum) where the column number is stored as an int2. This is needed to support different key data types in different columns. This much of the tuple is built by index_form_tuple according to the usual rules. ...
createindexmulticolumn_indexonemployees(name,salary); 结果2: 示例3:(如果表中有同样的行,就会报错) create uniqueindexunique_on_nameonemployees(name); 结果3: 2.删除索引 语法: DROPINDEX index_name; 示例: dropindexmulticolumn_index; 注意事项: ...
此外，Replay日志记录时需保证幂等操作，即无论Replay多少次，结果都应该保持一致。例如，假设有一个add操作redo/undo: {Add, TupleID,ColumnIndex, 10},给指定的某个列的super加10。这个操作不是幂等的，因为执行一次和执行多次的结果是不同的。在实际应用中，必须注意这类非幂等操作的处理。事务日志是一个序列的...
Creating a multicolumn index in PostgreSQL is a common practice when we want to create an index on multiple columns. 在PostgreSQL 中创建多列索引是一种常见的做法,因为我们要在多列上创建索引。 PostgreSQL Index Types The PostgreSQL index facilitates the efficient retrieval of data from the table. Th...
index_getprocinfo - get a support procedure's lookup info 1. index_open函数通过relation OID打开一个index relation,主要是通过调用relation.c中函数获取RelationData结构体,PostgreSQL数据库RelationAM——relation related routines。 Relationindex_open(OidrelationId,LOCKMODElockmode) { ...
index_scan | f bitmap_scan | t backward_scan | f 唯一可用的扫描技术是位图扫描。由于索引总是被完全扫描,因此实现按TID逐行返回行的常规索引访问没有意义。 1 2 3 4 5 6 7 8 9 10 11 name| pg_index_column_has_property ---+--- asc| f desc| f nulls_first | f nulls_last | f order...