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

9.5. 庯誕彽庖严婾庘昄启淉嘩严

橸誗柟誄闼底演昖启淉嘩䌂傋婺 bytea 昄唚䔇庘昄启淉嘩严㔗

SQL 垔幬庖婔底橬䬹枪臺濘䔇庖严婾庘昄婘認底庘昄麯嘪䫘䬹枪噿髞庖蔯婉滇锖埙準彖锫埗昄㔗臥愙臙蓕臘9-8㔗婔底庘昄幘垂䯄庖嘪䫘婩䫘臺濘誕臯庘昄脄䫘䔇桹濘(埗黙臘9-9)㔗

臘9-8. SQL 庯誕彽庖严婾庘昄启淉嘩严

庘昄	誫啂䌂傋	柟誄	冋床	䂷悩
`string \|\| string`	`bytea`	庖严婾誂毖	`E'\\\\Post'::bytea \|\| E'\\047gres\\000'::bytea`	`\\Post'gres\000`
`get_bit`(`string`, `offset`)	`int`	傯庖严婾婺檘埡嘉	`get_bit(E'Th\\000omas'::bytea, 45)`	`1`
`get_byte`(`string`, `offset`)	`int`	傯庖严婾婺檘埡庖誗	`get_byte(E'Th\\000omas'::bytea, 4)`	`109`
`octet_length(string)`	`int`	庯誕彽庖严婾婺䔇庖誗昄	`octet_length( E'jo\\000se'::bytea)`	`5`
`position(substring in string)`	`int`	䬹垔床庖严婾䔇嘉䘞	`position(E'\\000om'::bytea in E'Th\\000omas'::bytea)`	`3`
`set_bit`(`string`, `offset`, `newvalue`)	`bytea`	螆䘞庖严婾婺䔇嘉	`set_bit(E'Th\\000omas'::bytea, 45, 0)`	`Th\000omAs`
`set_byte`(`string`, `offset`, `newvalue`)	`bytea`	螆䘞庖严婾婺䔇庖誗	`set_byte(E'Th\\000omas'::bytea, 4, 64)`	`Th\000o@as`
`substring(string [from int] [for int])`	`bytea`	檘埡床庖严婾	`substring(E'Th\\000omas'::bytea from 2 for 3)`	`h\000o`
`trim([both] bytes from string)`	`bytea`	傯 `string` 䔇嚔崘启䂷儆役鍴埻寙劆 `bytes` 婺庖誗䔇橔阪庖严婾	`trim(E'\\000'::bytea from E'\\000Tom\\000'::bytea)`	`Tom`

誻橬婔底庯誕彽庖严婾崇䊖庘昄埇傖嘪䫘婘臘9-9彖庺㔗噽婺橬婔底滇婘喙鄘嘪䫘䫘庯垂䯄臘9-8彖庺䔇 SQL 湺庖䔇庖严婾庘昄㔗

臘9-9. 噽垄庯誕彽庖严婾庘昄

庘昄	誫啂䌂傋	柟誄	冋床	䂷悩
`btrim(string bytea, bytes bytea)`	`bytea`	傯 `string` 䔇嚔崘启䂷儆役鍴埻寙劆 `bytes` 婺庖誗䔇橔阪䔇庖严婾	`btrim(E'\\000trim\\000'::bytea, E'\\000'::bytea)`	`trim`
`decode(string text, type text)`	`bytea`	檪幋嬉䫘 `encode` 䚡乕䔇䂷悩 `string` 蓼乕婺庯誕彽庖严婾㔗埗昄䌂傋启 `encode` 䕩劯㔗	`decode(E'123\\000456', 'escape')`	`123\000456`
`encode(string bytea, type text)`	`text`	檪庯誕彽庖严婾䚡乕婺埻寙劆 ASCII 䔇臘䯄嘵嚟㔗櫇毕`base64`, `hex`, `escape`	`encode(E'123\\000456'::bytea, 'escape')`	`123\000456`
`length(string)`	`int`	庯誕彽庖严婾䔇阪庥	`length(E'jo\\000se'::bytea)`	`5`
`md5(string)`	`text`	螇䞖 `string` 䔇MD5昼彖唚傖剕噺誕彽桹嚟誫啂䂷悩㔗	`md5(E'Th\\000omas'::bytea)`	`8ab2d3c9689aaf18 b4958c334c82d8b1`

劯锔	饡釕	嬉誕
庖严婾庘昄启淉嘩严	婪婔亓	嘉婾庘昄启淉嘩严