In RANGE mode, these options require that the ORDER BY clause specify exactly one column. The offset specifies the maximum difference between the value of that column in the current row and its value in precedin
ORDER BY <Ordering Expression> [ ASC | DESC ] [ ,...n ] OFFSET <Offset Expression> { ROW | ROWS } [FETCH { FIRST | NEXT } <Page Size Expression> { ROW | ROWS } ONLY ] Examples The following example creates the OrderItems table. CREATE TABLE OrderItems ...
class ArrayAgg(expression, distinct=False, filter=None, default=None, ordering=(), **extra)¶ 返回一个值的列表,包括空值,串联成一个数组,如果没有值,则返回 default。 distinct¶ 一个可选的布尔参数,用于确定数组值是否会被去重。默认值为 False。 ordering¶ 可选的字段名字符串(可选的 "-" 前...
聚合函数是从一组输入中计算出一个结果的函数。 测试表 test=# \d tbl_test Table "public.tbl_test" Column | Type | Modifiers ---+---+--- id | integer | name | character varying(32) | sex | character varying(1) | test=# select * from tbl_test; id | name | sex ---+---+-...
距离函数是为索引元素调用的,它必须计算从表达式(“indexed-field ordering-operator expression”)定义的值到给定元素的距离。对于叶元素,这只是到索引值的距离。对于内部元素,函数必须返回到子叶元素的最小距离。由于遍历所有子行代价很高,因此允许该函数乐观地低估距离,但以降低搜索效率为代价。但是,决不允许函数高估距...
(void) get_equality_op_for_ordering_op(sortOperator, &reverse); } /* Add NULLS FIRST/LAST only if it wouldn't be default */ if (nullsFirst && !reverse) { appendStringInfoString(buf, " NULLS FIRST"); } else if (!nullsFirst && reverse) { appendStringInfoString(buf, " NULLS LAST"...
* us represent knowledge about different sort orderings being equivalent. * Since every PathKey must reference an EquivalenceClass, we will end up * with single-member EquivalenceClasses whenever a sort key expression has * not been equivalenced to anything else. It is also possible that such an...
Ordering & Limiting Rows In this section, you’ll learn how to sort rows by values in one or more columns and limit the number of rows a query returns. ORDER BY –Sort rows by one or more columns. LIMIT –Return only a subset of rows from a query. FETCH –Work like the LIMIT ...
double rows; /* estimated number of result tuples */ Cost startup_cost; /* cost expended before fetching any tuples */ Cost total_cost; /* total cost (assuming all tuples fetched) */ List *pathkeys; /* sort ordering of path's output */ /* pathkeys is a List of PathKey nodes;...
ScanState ss;/* its first field is NodeTag */List *indexqual;//execution state for indexqual expressionsScanKey ioss_ScanKeys;//Skey structures for index qualsintioss_NumScanKeys;//number of ScanKeysScanKey ioss_OrderByKeys;//Skey structures for index ordering operatorsintioss_NumOrderByKe...