array_prepend(anyelement, anyarray) anyarray 向一个数组开头附加一个元素 array_prepend(1, ARRAY[2,3]) {1,2,3} array_dims(anyarray) text 返回一个数组维数的文本表示 array_dims(ARRAY[[1,2,3], [4,5,6]]) [1:2][1:3] array_lower(anyarray, int) int 返回指定的数组维数的下界 array...
在之前的文章中,我们讨论了PostgreSQL索引引擎和访问方法的接口,以及哈希索引、b-tree、GiST、SP-GiST、GIN、RUM和BRIN。现在我们来看看Bloom索引。 典型的布隆过滤器是一种数据结构,使我们能够快速检查集合中元素的成员关系。过滤器是非常紧凑,但允许存在错误:it can mistakenly consider an element to be a member ...
if any */bool agg_star;/* argument was really '*' */bool agg_distinct;/* arguments were labeled DISTINCT */bool func_variadic;/* last argument was labeled
The array * elements are like a normal ScanKey array except that: * sk_flags must include SK_ROW_MEMBER, plus SK_ROW_END in the last * element (needed since row header does not include a count) * sk_func points to the btree comparison support function for the * opclass, NOT the ...
i_index := outpatient_visits.FIRST; -- Get first element of array WHILE i_index IS NOT NULL LOOP DBMS_Output.PUT_LINE ('outpatient visits of ' || i_index || ' is ' || outpatient_visits(i_index)); i_index := outpatient_visits.NEXT(i_index); -- Get next element of array ...
element_type 是元素类型 identifier 是用户使用自定义类型定义的变量 数组和嵌套表的区别: 关键字不同:table、varray 长度限制不同:table没有长度限制、varray有长度限制 3.举例 declare type type_arr_varchar2 is varray(10) of varchar2(20); v_arr type_arr_varchar2; ...
/** A "distinct elements count histogram" slot describes the distribution of* the number of distinct element values present in each row of an array-type* column. Only non-null rows are considered, and only non-null elements.* staop contains the equality operator appropriate to the element ty...
* BackendId.(Note: valid BackendIds run from 1 to MaxBackends; element * zero of each array is never used.) * * OldestMemberMXactId[k] is the oldest MultiXactId each backend's current * transaction(s) could possibly be a member of, or InvalidMultiXactId ...
name | pg_index_column_has_property ---+--- asc | f desc | f nulls_first | f nulls_last | f orderable | f search_array | f search_nulls | t 可见,不支持排序,不能查询数组,支持索引 NULL 值。 但是剩下的两个属性,distance_orderable 和 returnable,取决于所使用的运算符类。例如,对点而...
regexp_split_to_array函数的行为和regexp_split_to_table相同,不过regexp_split_to_array会把它的结果以一个text数组的形式返回。它的语法是regexp_split_to_array(string, pattern [, flags ])。这些参数和regexp_split_to_table的相同。 一些例子: ...