CREATE AGGREGATE

中文man手册

目录

NAME CREATE AGGREGATE
SYNOPSIS .sp .nf CREATE AGGREGATE
DESCRIPTION 描述
PARAMETERS 参数
EXAMPLES 例子
COMPATIBILITY 兼容性
SEE ALSO 参见
译者
跋

CREATE AGGREGATE

NAME
SYNOPSIS
DESCRIPTION æè¿°
PARAMETERS åæ°
EXAMPLES ä¾å
COMPATIBILITY å¼å®¹æ§
SEE ALSO åè§
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NAME

CREATE AGGREGATE - å®ä¹ä¸ä¸ªæ°çèéå½æ°

SYNOPSIS

CREATE AGGREGATE name (
BASETYPE = input_data_type,
SFUNC = sfunc,
STYPE = state_data_type
[ , FINALFUNC = ffunc ]
[ , INITCOND = initial_condition ]
)

DESCRIPTION æè¿°

CREATE AGGREGATE å®ä¹ä¸ä¸ªæ°çèéå½æ°ã ä¸äºç¨äºåºæ¬ç±»åçèéå½æ°å¦ min(integer) å avg(double precision) çå·²ç»åå«å¨åºç¡è½¯ä»¶åéäºã å¦æä½ éè¦å®ä¹ä¸ä¸ªæ°ç±»åæéè¦ä¸ä¸ªè¿æ²¡ææä¾çèéå½æ°ï¼è¿æ¶ä¾¿å¯ç¨ CREATE AGGREGATE æ¥æä¾æä»¬æéè¦çç¹æ§ã

å¦æç»åºäºä¸ä¸ªæ¨¡å¼çååï¼æ¯å¦ï¼CREATE AGGREGATE myschema.myagg ...ï¼ï¼é£ä¹è¯¥èéå½æ°æ¯å¨æå®æ¨¡å¼ä¸åå»ºçã å¦åå®æ¯å¨å½åæ¨¡å¼ä¸åå»ºçã

ä¸ä¸ªèéå½æ°æ¯ç¨å®çåååè¾å¥æ°æ®ç±»åæ¥æ è¯çã åä¸æ¨¡å¼ä¸- å¦æä¸¤ä¸ªèéå¤ççè¾å¥æ°æ®ä¸åï¼å®ä»¬å¯ä»¥æç¸åçååã ä¸ä¸ªèéå½æ°çè¾å¥æ°æ®ç±»åå¿é¡»åææåä¸æ¨¡å¼ä¸çæ®éå½æ°çåååè¾å¥ç±»åä¸åã

ä¸ä¸ªèéå½æ°æ¯ç¨ä¸ä¸ªæä¸¤ä¸ªæ®éå½æ°åæçï¼ ä¸ä¸ªç¶æè½¬æ¢å½æ° sfunc, åä¸ä¸ªå¯éçç»è®¡ç®å½æ° ffunc. å®ä»¬æ¯è¿æ ·ä½¿ç¨çï¼

sfunc( internal-state, next-data-item ) ---> next-internal-state
ffunc( internal-state ) ---> aggregate-value

PostgreSQL åå»ºä¸ä¸ªç±»åä¸º stypeçä¸´æ¶åéã å®ä¿åè¿ä¸ªèéçå½ååé¨ç¶æã å¯¹äºæ¯ä¸ªè¾å¥æ°æ®æ¡ç®ï¼ é½è°ç¨ç¶æè½¬æ¢å½æ°è®¡ç®åé¨ç¶æå¼çæ°æ°å¼ã å¨å¤çå®æææ°æ®åï¼è°ç¨ä¸æ¬¡æç»å¤çå½æ°ä»¥è®¡ç®èéçè¿åå¼ã å¦ææ²¡ææç»å¤çå½æ°ï¼é£ä¹å°æåçç¶æå¼å½åè¿åå¼ã

ä¸ä¸ªèéå½æ°è¿å¯è½æä¾ä¸ä¸ªåå§æ¡ä»¶ï¼ä¹å°±æ¯è¯´ï¼æç¨çè¯¥åé¨ç¶æå¼çåå§å¼ã è¿ä¸ªå¼æ¯ä½ä¸ºä¸ä¸ªç±»åä¸º text çåæ®µåå¨å¨æ°æ®åºéçï¼ ä¸è¿å®ä»¬å¿é¡»æ¯ç¶æå¼æ°æ®ç±»åçåæ³çå¤é¨è¡¨ç°å½¢å¼çå¸¸éã å¦ææ²¡ææä¾ç¶æï¼é£ä¹ç¶æå¼åå§åä¸º NULLã

å¦æè¯¥ç¶æè½¬æ¢å½æ°è¢«å®ä¹ä¸º "strict"ï¼ é£ä¹å°±ä¸è½ç¨ NULL è¾å¥è°ç¨å®ãè¿ä¸ªæ¶åï¼å¸¦æè¿æ ·çè½¬æ¢å½æ°çèéæ§è¡èµ·æ¥çç°è±¡å¦ä¸æè¿°ã NULL è¾å¥çå¼è¢«å¿½ç¥ï¼ä¸è°ç¨æ¤å½æ°å¹¶ä¸ä¿çåä¸ä¸ªç¶æå¼ï¼ãå¦æåå§ç¶æå¼æ¯ NULLï¼é£ä¹ç±ç¬¬ä¸ä¸ªé NULL å¼æ¿æ¢è¯¥ç¶æå¼ï¼ èç¶æè½¬æ¢å½æ°ä»ç¬¬äºä¸ªé NULL çè¾å¥å¼å¼å§è°ç¨ãè¿æ ·åè®©æä»¬æ¯è¾å®¹æå®ç°è±¡ max è¿æ ·çèéã è¯·æ³¨æè¿ç§è¡ä¸ºåªæ¯å½ state_type ä¸ input_data_type ç¸åçæ¶åæè¡¨ç°åºæ¥ã å¦æè¿äºç±»åä¸åï¼ä½ å¿é¡»æä¾ä¸ä¸ªé NULL çåå§æ¡ä»¶æèä½¿ç¨ä¸ä¸ªéstriceçç¶æè½¬æ¢å½æ°ã

å¦æç¶æè½¬æ¢å½æ°ä¸æ¯ strictï¼ä¸¥æ ¼ï¼çï¼ é£ä¹å®å°æ æ¡ä»¶å°ä¸ºæ¯ä¸ªè¾å¥å¼è°ç¨ï¼ å¹¶ä¸å¿é¡»èªè¡å¤ç NULL è¾å¥å NULL è½¬æ¢å¼ï¼ è¿æ ·å°±åè®¸èéçä½èå¯¹èéä¸çç©ºå¼æå®å¨çæ§å¶ã

å¦æç»è½¬æ¢å½æ°å®ä¹ä¸º"strict"ï¼åå¦ææç»ç¶æå¼æ¯ NULL æ¶å°±ä¸ä¼è°ç¨å®ï¼ èæ¯èªå¨è¾åºä¸ä¸ªNULLçç»æãï¼å½ç¶ï¼è¿ææ¯ strict å½æ°çæ£å¸¸ç¹å¾ãï¼ ä¸ç®¡æ¯é£ç§æåµï¼ç»å¤çå½æ°å¯ä»¥éæ©è¿å NULLãæ¯å¦ï¼ avg çç»å¤çå½æ°å¨é¶è¾å¥è®°å½æ¶å°±ä¼è¿å NULLã

PARAMETERS åæ°

name

è¦åå»ºçèéå½æ°åï¼å¯ä»¥ææ¨¡å¼ä¿®é¥°çï¼ã

input_data_type

æ¬èéå½æ°è¦å¤ççåºæ¬æ°æ®ç±»åã å¯¹äºä¸æ£æ¥è¾å¥ç±»åçèéæ¥è¯´ï¼è¿ä¸ªåæ°å¯ä»¥å£°æä¸º"ANY"ã ï¼æ¯å¦ count(*)ï¼ã

sfunc

ç¨äºå¤çæºæ°æ®åéçæ¯ä¸ä¸ªè¾å¥æ°æ®çç¶æè½¬æ¢å½æ°åç§°ã å®éå¸¸æ¯ä¸ä¸ªååæ°çå½æ°ï¼ç¬¬ä¸ä¸ªåæ°çç±»åæ¯ state_data_type èç¬¬äºä¸ªåæ°çç±»åæ¯ input_data_type. å¦å¤ï¼å¯¹äºä¸ä¸ªä¸æ£æ¥è¾å¥æ°æ®çèéï¼è¯¥å½æ°åªæ¥åä¸ä¸ªç±»åä¸º state_data_type çåæ°ã ä¸ç®¡æ¯åªç§æåµï¼æ- ¤å½æ°å¿é¡»è¿åä¸ä¸ªç±»åä¸º state_data_typeçå¼ã è¿ä¸ªå½æ°æ¥åå½åç¶æå¼åå½åè¾å¥æ°æ®æ¡ç®ï¼èè¿åä¸ä¸ªç¶æå¼ã

state_data_type

èéçç¶æå¼çæ°æ®ç±»åã

ffunc

å¨è½¬æ¢å®ææè¾å¥å/åæ®µåè°ç¨çæç»å¤çå½æ°ãå®è®¡ç®èéçç»æã æ- ¤å½æ°å¿é¡»æ¥åä¸ä¸ªç±»åä¸º state_data_type çåæ°ã èéçè¾åºæ°æ®ç±»åè¢«å®ä¹ä¸ºæ¤å½æ°çè¿åç±»åã å¦ææ²¡æå£°æ ffunc åä½¿ç¨èéç»æçç¶æå¼ä½ä¸ºèéçç»æï¼èè¾åºç±»åä¸º state_data_typeã

initial_condition

ç¶æå¼çåå§è®¾ç½®ï¼å¼ï¼ãå®å¿é¡»æ¯ä¸ä¸ªæ°æ®ç±»å state_data_type å¯ä»¥æ¥åçææ¬å¸¸éå¼ã å¦ææ²¡æå£°æï¼ç¶æå¼åå§ä¸º NULLã

CREATE AGGREGATE çåæ°å¯ä»¥ä»¥ä»»ä½é¡ºåºä¹¦åï¼èä¸åªæ¯ä¸é¢æ¾ç¤ºçé¡ºåºã

EXAMPLES ä¾å

åé ‘‘User-defined Aggregates’’

COMPATIBILITY å¼å®¹æ§

CREATE AGGREGATE æ¯ PostgreSQL è¯è¨çæ©å±ã å¨ SQL æ åéæ²¡æ CREATE AGGREGATEã

SEE ALSO åè§

ALTER AGGREGATE [alter_aggregate(7)], DROP AGGREGATE [drop_aggregate(l)]

è¯è

Postgresql ä¸æç½ç« ä½ä¼å¹³ <laser@pgsqldb.org>

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