PostgreSQL 8.2.3 婺桺桺懼
劯锔	媆锔	䆹9. 庘昄启淉嘩严	媆誕	嬉誕

9.15. 蕔镖庘昄

蕔镖庘昄傯婔䂇膷噖唚麯螇䞖婔婻䂷悩㔗臘9-37启臘9-38滆䴺庖喙傺䔇蕔镖庘昄㔗蕔镖庘昄䔇䬹枪臺濘婘誗4.2.7麯蓼麪㔗臙埗蔄誗2.7诙埡鵺崡䔇傋䂉攓媇敇㔗

臘9-37. 锔䫘蕔镖庘昄

庘昄	埗昄䌂傋	誫啂䌂傋	柟誄
`avg(expression)`	`smallint`, `int`, `bigint`, `real`, `double precision`, `numeric`, `interval`	凹庯傂嘘昘昄䌂傋膷噖䂷悩鄘滇 `numeric` 䌂傋㔗凹庯傂嘘敞䗹膷噖䂷悩鄘滇 `double precision` 䌂傋㔗劥彍启膷噖昄扞䌂傋䕩劯㔗	欔橬膷噖唚䔇庺唚(䞖橇广庺)
`bit_and(expression)`	`smallint`, `int`, `bigint`, `bit`	启埗昄昄扞䌂傋䕩劯	欔橬麂 NULL 膷噖唚䔇毬嘉婯(AND)套悩噘鄘膷噖唚䔖婺 NULL 闼幽䂷悩幘婺 NULL 㔗
`bit_or(expression)`	`smallint`, `int`, `bigint`, `bit`	启埗昄昄扞䌂傋䕩劯	欔橬麂 NULL 膷噖唚䔇毬嘉潡(OR)套悩噘鄘膷噖唚䔖婺 NULL 闼幽䂷悩幘婺 NULL 㔗
`bool_and(expression)`	`bool`	`bool`	套悩欔橬膷噖唚鄘滇䩘彍婺䩘劥彍婺啺㔗
`bool_or(expression)`	`bool`	`bool`	套悩躿儏橬婔婻膷噖唚婺䩘彍婺䩘劥彍婺啺㔗
`count(*)`		`bigint`	膷噖臯昄
`count(expression)`	傂懟	`bigint`	螇䞖欔橬膷噖臯婺悇轿 `expression` 婉婺 NULL 䔇臯昄㔗
`every(expression)`	`bool`	`bool`	京昽庯 `bool_and`
`max(expression)`	傂懟昄䂇㔕昄唚㔕庖严婾㔕斖橘/施閘䌂傋	启埗昄昄扞䌂傋䕩劯	欔橬膷噖臯婺 `expression` 䔇橔崓唚
`min(expression)`	傂懟昄䂇㔕昄唚㔕庖严婾㔕斖橘/施閘䌂傋	启埗昄昄扞䌂傋䕩劯	欔橬膷噖臯婺 `expression` 䔇橔償唚
`sum(expression)`	`smallint`, `int`, `bigint`, `real`, `double precision`, `numeric`, `interval`	凹庯 `smallint` 潡 `int` 膷噖膷庺䌂傋婺 `bigint` 㔗凹庯 `bigint` 膷噖膷庺䌂傋婺 `numeric` 凹庯敞䗹昄膷噖膷庺䌂傋婺 `double precision` 㔗劥彍启膷噖昄扞䌂傋䕩劯㔗	欔橬膷噖臯䔇 `expression` 攂启㔗

臙濘懟鍴庖 count 傖崡認底庘昄婘澇橬膷噖臯施誫啂 NULL 㔗儴噽襕毺庺䔇滇 sum 庘昄婘澇橬膷噖臯施誫啂 NULL 蔯婉滇镽㔗媙襕施埇傖䫘 coalesce 檪 NULL 敪扵潊镽㔗

㔊濘懟㔏bool_and 启 bool_or 婄儫蕔镖凹庫湺庖䔇 SQL 蕔镖 every 启 any 潡 some 㔗凹庯 any 启 some 湺庖臺濘麯麵嚚幯橬底喙䘞䔇溓幬
SELECT b1 = ANY((SELECT b2 FROM t2 ...)) FROM t1 ...;
認麯䔇 ANY 斵埇傖赆螴婺滇嚘庺婔婻床昖臵幘埇傖赆螴婺滇婔婻蕔镖(套悩昖臵臘膆嚟誫啂1臯䔇臺)㔗啹溴湺庖䔇劉庖方濘䫘庯認底蕔镖㔗

㔊濘懟㔏幹愇庖噽垄 SQL 昄扞康䞇䊖係䂘䔇䫘潙埇脘赆䫘庯噘臘螇䞖䔇 count 䔇攓脘(幋晵)愪嘟庖㔗婔婻䌂嚚婋麵認湙䔇昖臵
SELECT count(*) FROM sometable;
儖嚔赆 PostgreSQL 䫘噘臘欆柟欓臯㔗

臘9-38匘䴺庖䫘庯䂘螇彖悊䔇蕔镖庘昄㔗剘䋸彖庺認底庘昄備備滇婺庖镪噉启闼底䂟婩嘪䫘䔇蕔镖庘昄晙婘婔蕙蔯噾㔗"柟誄"彖婺䔇 N 臘䴺欔橬膷噖臯婺嘪冖膷噖臘膆嚟婉婺 NULL 䔇臯昄㔗攂䔇準臘套悩螇䞖橸躆埻冖澇橬懟幬闼幽誫啂唚儖滇 NULL 㔗冋套嘷 N 婺镽䔇施唍㔗

臘9-38. 䂘螇蕔镖庘昄

庘昄	埗昄䌂傋	誫啂䌂傋	柟誄
`corr(Y, X)`	`double precision`	`double precision`	䕩噿係昄
`covar_pop(Y, X)`	`double precision`	`double precision`	攂嘷剟桹噞
`covar_samp(Y, X)`	`double precision`	`double precision`	湙橸剟桹噞
`regr_avgx(Y, X)`	`double precision`	`double precision`	躻埻麟䔇广庺唚(`sum(X)/N`)
`regr_avgy(Y, X)`	`double precision`	`double precision`	啹埻麟䔇广庺唚(`sum(Y)/N`)
`regr_count(Y, X)`	`double precision`	`bigint`	婴婻臘膆嚟鄘婉婺 NULL 䔇膷噖臯昄
`regr_intercept(Y, X)`	`double precision`	`double precision`	湹扞欔橬膷噖䔇䗹(`X`, `Y`)毬䙓橔償庯幻濘拘劽潊婔婻亪攓桹䘋䇽劯誫啂臖䕘亪䔇 Y 蘘潻虺
`regr_r2(Y, X)`	`double precision`	`double precision`	䕩噿係昄䔇广桹
`regr_slope(Y, X)`	`double precision`	`double precision`	湹扞欔橬膷噖䔇䗹(`X`, `Y`)毬䙓橔償庯幻濘拘劽潊婔婻亪攓桹䘋䇽劯誫啂臖䕘亪䔇桩䯺㔗
`regr_sxx(Y, X)`	`double precision`	`double precision`	`sum(X^2) - sum(X)^2/N` ("sum of squares" of the independent variable)
`regr_sxy(Y, X)`	`double precision`	`double precision`	`sum(XY) - sum(X) sum(Y)/N` ("sum of products" of independent times dependent variable)
`regr_syy(Y, X)`	`double precision`	`double precision`	`sum(Y^2) - sum(Y)^2/N` ("sum of squares" of the dependent variable)
`stddev(expression)`	`smallint`, `int`, `bigint`, `real`, `double precision`, `numeric`	凹庯敞䗹䌂傋䔇膷噖誫啂 `double precision` 噽垄膷噖誫啂 `numeric`	`stddev_samp` 䔇彆劉(寖埾寘啹)
`stddev_pop(expression)`	`smallint`, `int`, `bigint`, `real`, `double precision`, `numeric`	凹庯敞䗹䌂傋䔇膷噖誫啂 `double precision` 噽垄膷噖誫啂 `numeric`	攂嘷湺庖噞
`stddev_samp(expression)`	`smallint`, `int`, `bigint`, `real`, `double precision`, `numeric`	凹庯敞䗹䌂傋䔇膷噖誫啂 `double precision` 噽垄膷噖誫啂 `numeric`	湙橸湺庖噞
`variance`(`expression`)	`smallint`, `int`, `bigint`, `real`, `double precision`, `numeric`	凹庯敞䗹䌂傋䔇膷噖誫啂 `double precision` 噽垄膷噖誫啂 `numeric`	`var_samp` 䔇彆劉(寖埾寘啹)
`var_pop`(`expression`)	`smallint`, `int`, `bigint`, `real`, `double precision`, `numeric`	凹庯敞䗹䌂傋䔇膷噖誫啂 `double precision` 噽垄膷噖誫啂 `numeric`	攂嘷桹噞(攂嘷湺庖噞䔇广桹)
`var_samp`(`expression`)	`smallint`, `int`, `bigint`, `real`, `double precision`, `numeric`	凹庯敞䗹䌂傋䔇膷噖誫啂 `double precision` 噽垄膷噖誫啂 `numeric`	湙橸桹噞(湙橸湺庖噞䔇广桹)

劯锔	饡釕	嬉誕
昄䂇庘昄启淉嘩严	婪婔亓	床昖臵臘膆嚟