在PostgreSQL中,IS NOT DISTINCT FROM 是一个特殊的比较运算符,用于处理包括 NULL 值在内的比较。下面我会按照你的要求,分点详细解释 IS NOT DISTINCT FROM。 1. 解释"IS NOT DISTINCT FROM"在PostgreSQL中的含义 IS NOT DISTINCT FROM 用于判断两个值是否相等,包括当两个值都是 NULL 的情况。这与标准的 = ...
postgres=#select1isnotdistinctfromcast('1'asvarchar); ERROR: operator doesnotexist:integer=charactervaryingLINE1:select1isnotdistinctfromcast('1'asvarchar);^HINT: No operator matches the given nameandargument type(s). You might needtoaddexplicit type casts. postgres=#select1isnotdistinctfromcast('...
在postgresql/lightdb 开发过程中有时会用到 is distinct from 和 is not distinct from 这个功能。 is distinct from 功能描述 A和B的数据类型、值不完全相同返回 true A和B的数据类型、值完全相同返回 false 将空值视为相同。 postgres=# \x Expanded display is on. postgres=# select 1 is...
AND blocking_locks.DATABASE IS NOT DISTINCT FROM blocked_locks.DATABASE AND blocking_locks.relation IS NOT DISTINCT FROM blocked_locks.relation AND blocking_locks.page IS NOT DISTINCT FROM blocked_locks.page AND blocking_locks.tuple IS NOT DISTINCT FROM blocked_locks.tuple AND blocking_locks.virtua...
from pg_locks a,pg_stat_activity b where a.pid=b.pid and a.granted ), t_overlap as ( select r.* from t_wait w join t_run r on ( r.locktype is not distinct from w.locktype and r.database is not distinct from w.database and ...
FROM pg_catalog.pg_locks blocked_locks JOIN pg_catalog.pg_stat_activity blocked_activity ON blocked_activity.pid = blocked_locks.pid JOIN pg_catalog.pg_locks blocking_locks ON blocking_locks.locktype = blocked_locks.locktype AND blocking_locks. DATABASE IS NOT DISTINCT FROM blocked_locks. ...
from pg_locks a,pg_stat_activity b where a.pid=b.pid and a.granted ), t_overlap as ( select r.* from t_wait w join t_run r on ( r.locktype is not distinct from w.locktype and r.database is not distinct from w.database and ...
DISTINCT应用于输出结果,并且需要遵循SELECT,您不能在单个列上调用它。GROUP BY可以给出单列结果,如果这正是您需要的。 -- filter all results SELECT DISTINCT film_id, rental_rate FROM film; -- filter on rental_rate SELECT film_id, rental_rate FROM film GROUP BY rental_rate; -- syntax error SEL...
对于非空输入,IS DISTINCT FROM和<>操作符一样。不过,如果两个输入都为空,它会返回假。而如果只有一个输入为空,它会返回真。类似地,IS NOT DISTINCT FROM对于非空输入的行为与=相同,但是当两个输入都为空时它返回真,并且当只有一个输入为空时返回假。因此,这些谓词实际上把空值当作一种普通数据值而不是"unk...
b.xact_start,b.query_start,b.usename,b.datname,b.client_addr,b.client_port,b.application_namefrompg_locks a,pg_stat_activity bwherea.pid=b.pid and a.granted ), t_overlapas(selectr.*fromt_wait w join t_run r on ( r.locktypeisnot distinctfromw.locktype and ...