本节描述了用于检查和操作字符串数值的函数和操作符。在这个环境中的字符串包括所有 character, character varying, text 类型的值。除非另外说明,所有下面列出的函数都可以处理这些类型,不过要小心的是,在使用 character
SQL 定义了一些字符串函数,它们有指定的语法(用特定的关键字而不是逗号来分隔参数)。详情请见表9-5,这些函数也用正常的函数调用语法实现了(参阅表9-6)。
表9-5. SQL 字符串函数和操作符
函数 | 返回类型 | 描述 | 例子 | 结果 |
string || string | text | 字符串连接 | 'Post' || 'greSQL' | PostgreSQL |
| int | 字符串里二进制位的个数 | bit_length('jose') | 32 |
| int | 字符串中的字符个数 | char_length('jose') | 4 |
| text | 使用指定的转换名字改变编码。转换可以通过 CREATE CONVERSION 定义。当然系统里有一些预定义的转换名字。参阅表9-7获取可用的转换名。 | convert('PostgreSQL' using iso_8859_1_to_utf8) | UTF8编码的'PostgreSQL' |
| text | 把字符串转化为小写 | lower('TOM') | tom |
| int | 字符串中的字节数 | octet_length('jose') | 4 |
| text | 替换子字符串 | overlay('Txxxxas' placing 'hom' from 2 for 4) | Thomas |
| int | 指定的子字符串的位置 | position('om' in 'Thomas') | 3 |
| text | 抽取子字符串 | substring('Thomas' from 2 for 3) | hom |
| text | 抽取匹配 POSIX 正则表达式的子字符串。参见节9.7获取更多关于模式匹配的信息。 | substring('Thomas' from '...$') | mas |
| text | 抽取匹配 SQL 正则表达式的子字符串。参见节9.7获取更多关于模式匹配的信息。 | substring('Thomas' from '%#"o_a#"_' for '#') | oma |
| text | 从字符串 string 的开头/结尾/两边删除只包含 characters | trim(both 'x' from 'xTomxx') | Tom |
| text | 把字符串转化为大写 | upper('tom') | TOM |
还有额外的字符串操作函数可以用,它们在表9-6列出。它们有些在内部用于实现表9-5列出的 SQL 标准字符串函数。
表9-6. 其它字符串函数
函数 | 返回类型 | 描述 | 例子 | 结果 |
| int | 参数第一个字符的 ASCII 码 | ascii('x') | 120 |
| text | 从 string 开头和结尾删除只包含 characters | btrim('xyxtrimyyx', 'xy') | trim |
| text | 给出 ASCII 码的字符 | chr(65) | A |
| text | 把原来编码为 src_encoding 的字符串转换为 dest_encoding 编码(如果省略了src_encoding | convert( 'text_in_utf8', 'UTF8', 'LATIN1') | 以ISO 8859-1编码表示的text_in_utf8 |
| bytea | 把早先用 | decode('MTIzAAE=', 'base64') | 123\000\001 |
| text | 把二进制数据编码为只包含 ASCII 形式的数据。支持的类型有:base64, hex,escape | encode( E'123\\000\\001', 'base64') | MTIzAAE= |
| text | 把每个单词的第一个子母转为大写,其它的保留小写。单词是一系列字母数字组成的字符,用非字母数字分隔。 | initcap('hi THOMAS') | Hi Thomas |
| int | string | length('jose') | 4 |
| text | 通过填充字符 fill(缺省时为空白),把 string 填充为 length 长度。如果string 已经比 length | lpad('hi', 5, 'xy') | xyxhi |
| text | 从字符串 string 的开头删除只包含 characters | ltrim('zzzytrim', 'xyz') | trim |
| text | 计算 string | md5('abc') | 900150983cd24fb0 d6963f7d28e17f72 |
| name | 当前客户端编码名称 | pg_client_encoding() | SQL_ASCII |
| text | 返回适用于 SQL 语句的标识符形式(使用适当的引号进行界定)。只有在必要的时候才会添加引号(字符串包含非标识符字符或者会转换大小写的字符)。嵌入的引号被恰当地写了双份。 | quote_ident('Foo bar') | "Foo bar" |
| text | 返回适用于在 SQL 语句里当作文本使用的形式。嵌入的引号和反斜杠被恰当地写了双份。 | quote_literal( 'O\'Reilly') | 'O''Reilly' |
| text | 替换匹配 POSIX 正则表达式的子字符串。参见节9.7以获取更多模式匹配的信息。 | regexp_replace('Thomas', '.[mN]a.', 'M') | ThM |
| text | 将 string 重复 number | repeat('Pg', 4) | PgPgPgPg |
| text | 把字符串 string 里出现地所有子字符串 from 替换成子字符串 to | replace( 'abcdefabcdef', 'cd', 'XX') | abXXefabXXef |
| text | 使用填充字符 fill(缺省时为空白),把 string 填充到 length 长度。如果string 已经比 length | rpad('hi', 5, 'xy') | hixyx |
| text | 从字符串 string 的结尾删除只包含 characters | rtrim('trimxxxx', 'x') | trim |
| text | 根据 delimiter 分隔 string 返回生成的第 field | split_part('abc~@~def~@~ghi', '~@~', 2) | def |
| int | 指定的子字符串的位置。和 position(substring in string) | strpos('high', 'ig') | 2 |
| text | 抽取子字符串。和 substring(string from from for count) | substr('alphabet', 3, 2) | ph |
| text | 把 string 从其它编码转换为 ASCII (仅支持 LATIN1, LATIN2, LATIN9, WIN1250编码)。 | to_ascii('Karel') | Karel |
| text | 把 number | to_hex(2147483647) | 7fffffff |
| text | 把在 string 中包含的任何匹配 from 中字符的字符转化为对应的在 to | translate('12345', '14', 'ax') | a23x5 |
表9-7. 内置的转换
ascii_to_mic | SQL_ASCII | MULE_INTERNAL |
ascii_to_utf8 | SQL_ASCII | UTF8 |
big5_to_euc_tw | BIG5 | EUC_TW |
big5_to_mic | BIG5 | MULE_INTERNAL |
big5_to_utf8 | BIG5 | UTF8 |
euc_cn_to_mic | EUC_CN | MULE_INTERNAL |
euc_cn_to_utf8 | EUC_CN | UTF8 |
euc_jp_to_mic | EUC_JP | MULE_INTERNAL |
euc_jp_to_sjis | EUC_JP | SJIS |
euc_jp_to_utf8 | EUC_JP | UTF8 |
euc_kr_to_mic | EUC_KR | MULE_INTERNAL |
euc_kr_to_utf8 | EUC_KR | UTF8 |
euc_tw_to_big5 | EUC_TW | BIG5 |
euc_tw_to_mic | EUC_TW | MULE_INTERNAL |
euc_tw_to_utf8 | EUC_TW | UTF8 |
gb18030_to_utf8 | GB18030 | UTF8 |
gbk_to_utf8 | GBK | UTF8 |
iso_8859_10_to_utf8 | LATIN6 | UTF8 |
iso_8859_13_to_utf8 | LATIN7 | UTF8 |
iso_8859_14_to_utf8 | LATIN8 | UTF8 |
iso_8859_15_to_utf8 | LATIN9 | UTF8 |
iso_8859_16_to_utf8 | LATIN10 | UTF8 |
iso_8859_1_to_mic | LATIN1 | MULE_INTERNAL |
iso_8859_1_to_utf8 | LATIN1 | UTF8 |
iso_8859_2_to_mic | LATIN2 | MULE_INTERNAL |
iso_8859_2_to_utf8 | LATIN2 | UTF8 |
iso_8859_2_to_windows_1250 | LATIN2 | WIN1250 |
iso_8859_3_to_mic | LATIN3 | MULE_INTERNAL |
iso_8859_3_to_utf8 | LATIN3 | UTF8 |
iso_8859_4_to_mic | LATIN4 | MULE_INTERNAL |
iso_8859_4_to_utf8 | LATIN4 | UTF8 |
iso_8859_5_to_koi8_r | ISO_8859_5 | KOI8 |
iso_8859_5_to_mic | ISO_8859_5 | MULE_INTERNAL |
iso_8859_5_to_utf8 | ISO_8859_5 | UTF8 |
iso_8859_5_to_windows_1251 | ISO_8859_5 | WIN1251 |
iso_8859_5_to_windows_866 | ISO_8859_5 | WIN866 |
iso_8859_6_to_utf8 | ISO_8859_6 | UTF8 |
iso_8859_7_to_utf8 | ISO_8859_7 | UTF8 |
iso_8859_8_to_utf8 | ISO_8859_8 | UTF8 |
iso_8859_9_to_utf8 | LATIN5 | UTF8 |
johab_to_utf8 | JOHAB | UTF8 |
koi8_r_to_iso_8859_5 | KOI8 | ISO_8859_5 |
koi8_r_to_mic | KOI8 | MULE_INTERNAL |
koi8_r_to_utf8 | KOI8 | UTF8 |
koi8_r_to_windows_1251 | KOI8 | WIN1251 |
koi8_r_to_windows_866 | KOI8 | WIN866 |
mic_to_ascii | MULE_INTERNAL | SQL_ASCII |
mic_to_big5 | MULE_INTERNAL | BIG5 |
mic_to_euc_cn | MULE_INTERNAL | EUC_CN |
mic_to_euc_jp | MULE_INTERNAL | EUC_JP |
mic_to_euc_kr | MULE_INTERNAL | EUC_KR |
mic_to_euc_tw | MULE_INTERNAL | EUC_TW |
mic_to_iso_8859_1 | MULE_INTERNAL | LATIN1 |
mic_to_iso_8859_2 | MULE_INTERNAL | LATIN2 |
mic_to_iso_8859_3 | MULE_INTERNAL | LATIN3 |
mic_to_iso_8859_4 | MULE_INTERNAL | LATIN4 |
mic_to_iso_8859_5 | MULE_INTERNAL | ISO_8859_5 |
mic_to_koi8_r | MULE_INTERNAL | KOI8 |
mic_to_sjis | MULE_INTERNAL | SJIS |
mic_to_windows_1250 | MULE_INTERNAL | WIN1250 |
mic_to_windows_1251 | MULE_INTERNAL | WIN1251 |
mic_to_windows_866 | MULE_INTERNAL | WIN866 |
sjis_to_euc_jp | SJIS | EUC_JP |
sjis_to_mic | SJIS | MULE_INTERNAL |
sjis_to_utf8 | SJIS | UTF8 |
tcvn_to_utf8 | WIN1258 | UTF8 |
uhc_to_utf8 | UHC | UTF8 |
utf8_to_ascii | UTF8 | SQL_ASCII |
utf8_to_big5 | UTF8 | BIG5 |
utf8_to_euc_cn | UTF8 | EUC_CN |
utf8_to_euc_jp | UTF8 | EUC_JP |
utf8_to_euc_kr | UTF8 | EUC_KR |
utf8_to_euc_tw | UTF8 | EUC_TW |
utf8_to_gb18030 | UTF8 | GB18030 |
utf8_to_gbk | UTF8 | GBK |
utf8_to_iso_8859_1 | UTF8 | LATIN1 |
utf8_to_iso_8859_10 | UTF8 | LATIN6 |
utf8_to_iso_8859_13 | UTF8 | LATIN7 |
utf8_to_iso_8859_14 | UTF8 | LATIN8 |
utf8_to_iso_8859_15 | UTF8 | LATIN9 |
utf8_to_iso_8859_16 | UTF8 | LATIN10 |
utf8_to_iso_8859_2 | UTF8 | LATIN2 |
utf8_to_iso_8859_3 | UTF8 | LATIN3 |
utf8_to_iso_8859_4 | UTF8 | LATIN4 |
utf8_to_iso_8859_5 | UTF8 | ISO_8859_5 |
utf8_to_iso_8859_6 | UTF8 | ISO_8859_6 |
utf8_to_iso_8859_7 | UTF8 | ISO_8859_7 |
utf8_to_iso_8859_8 | UTF8 | ISO_8859_8 |
utf8_to_iso_8859_9 | UTF8 | LATIN5 |
utf8_to_johab | UTF8 | JOHAB |
utf8_to_koi8_r | UTF8 | KOI8 |
utf8_to_sjis | UTF8 | SJIS |
utf8_to_tcvn | UTF8 | WIN1258 |
utf8_to_uhc | UTF8 | UHC |
utf8_to_windows_1250 | UTF8 | WIN1250 |
utf8_to_windows_1251 | UTF8 | WIN1251 |
utf8_to_windows_1252 | UTF8 | WIN1252 |
utf8_to_windows_1253 | UTF8 | WIN1253 |
utf8_to_windows_1254 | UTF8 | WIN1254 |
utf8_to_windows_1255 | UTF8 | WIN1255 |
utf8_to_windows_1256 | UTF8 | WIN1256 |
utf8_to_windows_1257 | UTF8 | WIN1257 |
utf8_to_windows_866 | UTF8 | WIN866 |
utf8_to_windows_874 | UTF8 | WIN874 |
windows_1250_to_iso_8859_2 | WIN1250 | LATIN2 |
windows_1250_to_mic | WIN1250 | MULE_INTERNAL |
windows_1250_to_utf8 | WIN1250 | UTF8 |
windows_1251_to_iso_8859_5 | WIN1251 | ISO_8859_5 |
windows_1251_to_koi8_r | WIN1251 | KOI8 |
windows_1251_to_mic | WIN1251 | MULE_INTERNAL |
windows_1251_to_utf8 | WIN1251 | UTF8 |
windows_1251_to_windows_866 | WIN1251 | WIN866 |
windows_1252_to_utf8 | WIN1252 | UTF8 |
windows_1256_to_utf8 | WIN1256 | UTF8 |
windows_866_to_iso_8859_5 | WIN866 | ISO_8859_5 |
windows_866_to_koi8_r | WIN866 | KOI8 |
windows_866_to_mic | WIN866 | MULE_INTERNAL |
windows_866_to_utf8 | WIN866 | UTF8 |
windows_866_to_windows_1251 | WIN866 | WIN |
windows_874_to_utf8 | WIN874 | UTF8 |
转换名[a] | 源编码 | 目的编码 |
【注意】a. 转换名遵循一个标准的命名模式:将源编码中的所有非字母数字字符用下划线替换,后面跟着 _to_ |