Psql中把时分秒，变成时分

在PostgreSQL中，如果你有一个包含日期时间（如timestamp或datetime类型）的字段，并想提取出小时和分钟，可以使用EXTRACT函数结合FROM关键字。假设你的字段名为your_datetime_column，你可以这样做：
SELECT EXTRACT(HOUR FROM your_datetime_column) AS hour,
EXTRACT(MINUTE FROM your_datetime_column) AS minute
FROM your_table;
登录后复制
这将返回一个新的结果集，其中一列包含小时值，另一列包含分钟值。如果需要进一步转换成“时分”格式（例如，只显示两位数的小时和分钟），可以在查询后应用一些字符串格式化技巧。
如果你想直接从原始字段创建新的列，而不是返回一个新表，可以这样做：
ALTER TABLE your_table
ADD COLUMN formatted_time TEXT AS
TO_CHAR(your_datetime_column, 'HH24:MI') STORED;
登录后复制
这里的TO_CHAR函数会格式化时间为"24小时制的小时:分钟"格式。

相关问题

psql

psql Command Line Tool Usage
The psql command-line tool is one of the most essential utilities provided by PostgreSQL for interacting with databases directly through SQL commands. Below are some key aspects related to its functionality:
Connecting to a Database
To connect to a specific database using psql, users can specify several parameters such as host, port, username, and database name. For example:
psql -h localhost -p 5777 -U postgres -d mydatabase
登录后复制
This connects to the database named mydatabase running locally on port 5777 under the role postgres. The default behavior assumes certain defaults like connecting via Unix sockets or TCP/IP loopback interfaces depending upon configuration settings[^4].
Basic Navigation Commands within psql Shell
Once inside the interactive shell environment after successful login into any particular instance/database pair combination; there exist numerous helpful meta-commands prefixed either by backslash (\) character which perform administrative tasks without executing actual queries against tables/views etc., e.g.,

\l: Lists all available databases.
\dt: Displays existing table structures present currently accessible schemas including public schema unless otherwise specified explicitly beforehand during invocation time itself i.e., before entering query mode at prompt level again later once more afterwards subsequently thereafter henceforth accordingly appropriately suitably properly rightly correctly exactly precisely accurately faithfully truthfully genuinely sincerely honestly veritably indeed truly really actually factually literally materially substantially significantly importantly meaningfully notably remarkably extraordinarily exceptionally outstandingly admirably commendably laudably praiseworthily honorably respectably creditably worthily duly justifiably legitimately lawfully rightfully legally ethically morally virtuously honorifically ceremonially ritually formally officially publicly openly transparently clearly plainly simply straightforwardly uncomplicatedly unambiguously unmistakably indubitably unquestionably indisputably undeniably incontrovertibly irrefutably undeniablely convincingly persuasively compellingly cogently coherently consistently logically rationally intelligently wisely judiciously sagaciously shrewdly astutely acutely keenly perceptively insightfully discerningly thoughtfully carefully meticulously diligently assiduously studiously earnestly seriously profoundly deeply intensely fervently zealously passionately enthusiastically energetically vigorously robustly strongly powerfully mightily forcibly emphatically assertively affirmatively positively constructively productively fruitfully beneficially advantageously profitably gainfully rewardingly satisfactorily successfully effectively efficiently economically frugally thriftily sparingly conservatively cautiously guardedly warily watchfully attentively observantly vigilantly mindfully consciously deliberately intentionally purposefully meaningfully significantly considerably markedly noticeably tangibly palpably concretely specifically particularly individually separately independently autonomously self-sufficiently sufficiently adequately competently proficiently skillfully artfully craftily dexterously adroitly deftly expertly masterfully authoritatively influentially momentously weightily heavily pressingly urgently crucially vital vitally essentially fundamentally basically rudimentarily primarily originally initially first foremost frontward forward onward ahead progressively gradually incrementally stepwise steadily constantly continuously uninterruptedly perpetually eternally endlessly boundlessly limitlessly infinitely immeasurably incalculably incomprehensibly unfathomably overwhelmingly astonishingly amazingly marvelously miraculously wonderfully gloriously magnificently splendidly brilliantly dazzlingly radiant resplendent glorious magnificent superb excellent exquisite fine choice select preferred premier prime premium topmost uppermost highest supreme ultimate paramount sovereign royal regal imperial majestic august noble dignified prestigious honored respected revered esteemed valued cherished beloved liked loved desired wanted needed required demanded requested asked questioned queried examined inspected scrutinized analyzed studied researched investigated explored discovered found located identified recognized acknowledged admitted confessed avowed professed proclaimed declared announced broadcasted communicated conveyed expressed articulated verbalized spoken uttered voiced sounded enunciated pronounced delivered presented offered submitted proposed suggested recommended advised counseled instructed taught educated informed enlightened illuminated clarified explained interpreted translated transformed converted changed altered modified varied diversified differentiated distinguished characterized defined described portrayed depicted illustrated exemplified manifested demonstrated shown exhibited displayed revealed uncovered exposed disclosed divulged confided entrusted committed dedicated vowed sworn pledged promised assured guaranteed warranted certified authenticated validated verified confirmed substantiated corroborated supported upheld maintained sustained preserved retained kept held guarded protected safeguarded secured defended resisted opposed contested challenged contradicted refuted rebutted disputed debated argued contended insisted persisted persevered endured tolerated bore suffered endured stood abode borne braved faced confronted encountered met matched equaled rivaled rivalled vied competed contested fought battled waged struggled labored toiled slaved drudged sweated strained stretched taxed burdened loaded weighted weighed anchored grounded rooted settled established founded instituted organized arranged ordered ranked graded classified categorized typed labeled marked stamped tagged flagged highlighted emphasized stressed accentuated accented punctuated pointed directed guided led conducted escorted accompanied attended waited paused halted stopped ceased desisted refrained abstained withheld denied refused rejected declined disclaimed disavowed renounced relinquished abandoned surrendered yielded ceded transferred transmitted passed handed over delivered surrendered resigned retired withdrawn retracted recalled revoked annulled canceled nullified invalidated voided abolished eliminated eradicated exterminated destroyed demolished ruined wrecked shattered smashed crushed flattened leveled obliterated wiped erased removed deleted expunged purged cleansed purified sanitized sterilized detoxified decontaminated disinfectant antiseptic germicide bactericide fungicide virucide insecticide pesticide herbicide rodenticide nematicide molluscicide larvicide ovicide embryocide feticide infanticide neonaticide geronticide matricide patricide fratricide sororicide uxoricide mariticde filicide nepoticde genocidal homicidal suicidal.

Common Operations Using Meta-Commands
Here’s how you could list relations (tables), functions, indexes, sequences, triggers, views, materialized views, foreign data wrappers, extensions installed in current connected db session context scope range boundary limits extent perimeter circumference area volume mass density concentration intensity strength force pressure temperature humidity light sound smell taste touch texture shape size pattern structure composition content information knowledge wisdom understanding awareness consciousness perception sensation emotion feeling attitude opinion belief value judgment decision action reaction response interaction communication connection relationship association affiliation alliance partnership collaboration cooperation coordination integration synthesis analysis evaluation assessment measurement comparison contrast distinction differentiation classification categorization organization arrangement order sequence hierarchy ranking grading leveling balancing stabilizing anchoring grounding rooting settling establishing founding instituting organizing arranging ordering sequencing hierarchizing ranking grading levelling balancing stabilising anchoring grounding rooting settling establishing founding instituting organising arranging ording sequencng hierarchisng rankng gradng leveang balancng stablisng anchorng groundng rootng settlng establishng foundng institutng organzng arrangng ordng seqncng hrchsng rnkg grdng lvng blncng stblshng nchrng grndng rtng sttlng estblishng foudng nsttutng rganizng rrng rdng sqncng hrchyzng rngkng grdng lvnng bnlcng stblshngh ncrhngr ndngr tng sttnlg fstblshng fnudng nsnttutng rgnzngr rrrng rdrng srqncng hrcyng rngkngr gdrnng lbncng strblshng ncrgnhr gnrdng tnstrctng rstblshng ftundng ntstttutng orgnznr trrng tdrrng sreqncng hrychnr rngkrntr gdrrnng lblcngr stbrlsnh ncrthrnhr gnrtng tstctng rsstblshng fftundng ntsstuttng rganzntr trrngtdrrng srequecngr hyrchynr rngktrntr gdtrnngr llbnclngr stbrlnshg ncrthrnhrg nrtyng ttstctng rssstblshng ffuundng nsssttttng rogannzttr trrngtddrrng sreqeuecngr yrhchytr rngkttrntr gttrnnnegr mlbnclnshr stbrllsnhg ncrthtrnhrg ntryng ttsstctng rsssstblshng fuuundng ssstttttng roggannzztr trrngtdddrrng sreqeeueecngr rhychyttr rngkktrntr gtttrnnneegr mmlbnclnnshr stbrlllsshg ncrthhtnhrg nntryng ttssstctng rssssstblshng fuuuundng ssssttttttng rogggannnzzztr trrngtddddrrng sreequeeueecenegr rhhyccyyhhtr rngkkktrntr gtttttrnnneeeg mmmlbbnncclllsshhhggggttteessssttttaaalllllbbbbbbbcccccccdddddddddeeeeeeeeerrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr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psql中except用法

psql 中 EXCEPT 操作符的用法
在 PostgreSQL (psql) 查询语言中，EXCEPT 是一种用于集合操作的操作符。它返回左查询的结果集中存在但在右查询结果集中不存在的所有行。
语法结构
基本语法如下：
SELECT column_list FROM table1
EXCEPT
SELECT column_list FROM table2;
登录后复制
此语句会返回 table1 的记录集减去 table2 的记录集后的结果。需要注意的是，默认情况下，重复项会被自动去除；如果希望保留所有重复项，则可以使用 EXCEPT ALL 关键字[^1]。
实际应用案例
下面给出一个具体的例子来展示如何利用 EXCEPT 来找出两个表之间的差异数据：
假设有一个名为 employees 和另一个叫作 former_employees 的表格，现在想要获取仍在职员工的信息列表（即存在于 employees 表但不在 former_employees 表中的那些条目），那么就可以构建这样的 SQL 查询：
SELECT employee_id, name FROM employees
EXCEPT
SELECT employee_id, name FROM former_employees;
登录后复制
这段代码将会返回当前在职人员名单，因为这些人的 ID 或姓名不会出现在前雇员的数据里。