最后一行是 UNBOUNDED FOLLOWING first_value 可以忽略 ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING last_value 不能忽略 ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING first_value(取值字段) OVER ( PARTITION BY 分组字段 ORDER BY 排序字段 ) as firstInfo, last_value(取值字段) OVER ( ...
COALESCE返回它的第一个非NULL的参数的值。它常用于在为显示目的检索数据时用缺省值替换NULL值。 COALESCE(value[, ...]) 和CASE表达式一样,COALESCE将不会计算不需要用来判断结果的参数。也就是说,在第一个非空参数右边的参数不会被计算。5.10.3 NULLIF当且仅当value1和value2相等时,NULLIF才返回NULL。否则它...
select e_no,e_name,e_salary from employee where e_salary is null; 1. 排序(默认升序 asc,降序desc) select e_no,e_name,e_salary,e_hireDate from employee order by e_salary asc,e_hireDate desc; 1. 空值排在前面(默认 nulls last) select e_no,e_name,e_salary from employee order by e...
SELECT * FROM people WHERE (first_name || ' ' || last_name) = 'John Smith'; 和上面的例子一样,尽管我们可能会为first_name和last_name分别创建独立索引,或者是基于这两个字段的复合索引,在执行该查询语句时,这些索引均不会被使用,该查询能够使用的索引只有我们下面创建的表达式索引。 CREATE INDEX peopl...
字典是启蒙教育时期,大家不可获取的好帮手字典是无序的术语和定义的集合,这意味着: · 每个数据点都有标识符(即术语)和值(即定义)。...author = { "first_name":"Jonathan", "last_name":"Hsu", "username":"jhsu98" ...
hive 获取数组的最大值和最小值 exploded_column,XXXX.column2 from XXXX LATERAL VIEW explode(XXXX.column1) t1 as exploded_column 2、使用first_value获取最小值...,last_value获取最大值 select uid,point_id, first_value(loc_x)over(partition by uid order by point_id) as start 5.3K40 ...
Do ORDER BY first because both * transformGroupClause and transformDistinctClause need the results. Note * that these functions can also change the targetList, so it's passed to * them by reference. */ qry->sortClause = transformSortClause(pstate, stmt->sortClause, &qry->targetList, EXPR...
department_idINT);-- 插入示例数据INSERTINTOdepartments (department_name)VALUES('HR'), ('Engineering');INSERTINTOemployees (first_name, last_name, department_id)VALUES('John','Doe',1), ('Jane','Smith',2), ('Jim','Brown',NULL); ...
-2表示这是一个NULL结尾的C字符串 通常为flase, 变长类型通常是传引用。即使TYPLEN允许传值,TYPBYVAL也可以为false。 如下所示,每种类型都有自己的typlen,typbyval,typalign,typstorage等。\d+ table_name可以查看当前表各字段的存储方式,storage字段中。 postgres=# \d+ student Table "public.student" ...
second_cteAS(SELECTcolumn1FROMfirst_cte-- 错误,不能在 second_cte 中引用 first_cteUNIONSELECTcolumn2FROMtable2 )SELECT*FROMsecond_cte; 6. 总结 CTE 是 PostgreSQL 中一个强大的查询工具,能够帮助用户简化复杂查询、提高代码的可读性和维护性。通过 CTE,用户可以轻松地定义和使用临时结果集,支持递归查询和数...