Datatype formatting functions:
PostgreSQL formatting functions provide a set of efficient tools for converting various datatypes (date/time, integer, floating point, and numeric) to formatted strings and back from formatted characters String to the specified data type. The functions are listed below, and they all follow a common calling convention: the first argument is the value to be formatted, and the second is a template that defines the output or output format.
PostgreSQL formatting functions provide a set of efficient tools for converting various datatypes (date/time, integer, floating point, and numeric) to formatted strings and back from formatted characters String to the specified data type. The functions are listed below, and they all follow a common calling convention: the first argument is the value to be formatted, and the second is a template that defines the output or output format.
| function | return type | describe | example |
| to_char(timestamp, text) | text | convert timestamp to string | to_char(current_timestamp, ‘HH12:MI:SS’) |
| to_char(interval, text) | text | Convert time interval to string | to_char(interval ‘15h 2m 12s’, ‘HH24:MI:SS’) |
| to_char(int, text) | text | convert integer to string | to_char(125, ‘999’) |
| to_char(double precision, text) | text | Convert Real/Double to String | to_char(125.8::real, ‘999D9’) |
| to_char(numeric, text) | text | convert numeric to string | to_char(-125.8, ‘999D99S’) |
| to_date(text, text) | date | convert string to date | to_date(‘05 Dec 2000’, ‘DD Mon YYYY’) |
| to_timestamp(text, text) | timestamp | convert string to timestamp | to_timestamp(‘05 Dec 2000’, ‘DD Mon YYYY’) |
| to_timestamp(double) | timestamp | Convert UNIX epoch to timestamp | to_timestamp(200120400) |
| to_number(text, text) | numeric | convert string to numeric | to_number(‘12,454.8-‘, ‘99G999D9S’) |
1. Patterns for date/time formatting:
| model | describe |
| HH | Hours of the day (01-12) |
| HH12 | Hours of the day (01-12) |
| HH24 | Hour of the day (00-23) |
| ME | minutes (00-59) |
| SS | Seconds (00-59) |
| MS | milliseconds (000-999) |
| US | Microseconds (000000-999999) |
| AM | noon sign (uppercase) |
| Y,YYY | year with comma (4 and more digits) |
| YYYY | Years (4 and more digits) |
| YYY | last three years |
| YY | last two years |
| AND | last of the year |
| MONTH | Full-length month name (9 characters padded with blanks) |
| Month | Full-length mixed-case month name (9 characters padded with blanks) |
| month | Full-length lowercase month name (9 characters padded with blanks) |
| MON | Uppercase abbreviated month name (3 characters) |
| Mon | Abbreviated mixed case month name (3 characters) |
| mon | Lowercase abbreviated month name (3 characters) |
| MM | Month number (01-12) |
| DAY | Date name in full length case (9 characters padded with blanks) |
| Day | Full-length mixed-case date name (9 characters padded with blanks) |
| day | Full-length lowercase date name (whitespace padded to 9 characters) |
| two | Abbreviated uppercase date name (3 characters) |
| two | Abbreviated mixed case date name (3 characters) |
| two | Abbreviated lowercase date name (3 characters) |
| DDD | Day of the year (001-366) |
| DD | Day of the month (01-31) |
| D | Day of the week (1-7; Sunday is 1) |
| W | Week number (1-5) in a month (the first week starts on the first day of the month) |
| WW | Week number in the year (1-53) (the first week starts on the first day of the year) |
2. Template mode for numeric formatting:
| model | describe |
| 9 | a value with the specified number of digits |
| 0 | value with leading zeros |
| . (Kukuten) | decimal point |
| ,(comma) | grouping (thousands) separator |
| PR | Negative values in angle brackets |
| S | signed value |
| L | currency symbol |
| D | decimal point |
| G | grouping separator |
| ME | minus sign at indicated position (if number < 0) |
| PL | plus sign at indicated position (if number > 0) |
| SG | plus/minus sign at the indicated position |
8. Time/date functions and operators:
1. The following is a list of time/date operators supported in PostgreSQL:
| operator | example | result |
| + | date ‘2001-09-28’ + integer ‘7’ | date ‘2001-10-05’ |
| + | date ‘2001-09-28’ + interval ‘1 hour’ | timestamp ‘2001-09-28 01:00’ |
| + | date ‘2001-09-28’ + time ‘03:00’ | timestamp ‘2001-09-28 03:00’ |
| + | interval ‘1 day’ + interval ‘1 hour’ | interval ‘1 day 01:00’ |
| + | timestamp ‘2001-09-28 01:00’ + interval ‘23 hours’ | timestamp ‘2001-09-29 00:00’ |
| + | time ‘01:00’ + interval ‘3 hours’ | time ‘04:00’ |
| - | - interval ‘23 hours’ | interval ‘-23:00’ |
| - | date ‘2001-10-01’ - date ‘2001-09-28’ | integer ‘3’ |
| - | date ‘2001-10-01’ - integer ‘7’ | date ‘2001-09-24’ |
| - | date ‘2001-09-28’ - interval ‘1 hour’ | timestamp ‘2001-09-27 23:00’ |
| - | time ‘05:00’ - time ‘03:00’ | interval ‘02:00’ |
| - | time ‘05:00’ - interval ‘2 hours’ | time ‘03:00’ |
| - | timestamp ‘2001-09-28 23:00’ - interval ‘23 hours’ | timestamp ‘2001-09-28 00:00’ |
| - | interval ‘1 day’ - interval ‘1 hour’ | interval ‘23:00’ |
| - | timestamp ‘2001-09-29 03:00’ - timestamp ‘2001-09-27 12:00’ | interval ‘1 day 15:00’ |
| * | interval ‘1 hour’ * double precision ‘3.5’ | interval ‘03:30’ |
| / | interval ‘1 hour’ / double precision ‘1.5’ | interval ‘00:40’ |
2. 日期/时间函数：
| 函数 | 返回类型 | 描述 | 例子 | 结果 |
| age(timestamp, timestamp) | interval | 减去参数，生成一个使用年、月的”符号化”的结果 | age(‘2001-04-10’, timestamp ‘1957-06-13’) | 43 years 9 mons 27 days |
| age(timestamp) | interval | 从current_date减去得到的数值 | age(timestamp ‘1957-06-13’) | 43 years 8 mons 3 days |
| current_date | date | 今天的日期 | ||
| current_time | time | 现在的时间 | ||
| current_timestamp | timestamp | 日期和时间 | ||
| date_part(text, timestamp) | double | 获取子域(等效于extract) | date_part(‘hour’, timestamp ‘2001-02-16 20:38:40’) | 20 |
| date_part(text, interval) | double | 获取子域(等效于extract) | date_part(‘month’, interval ‘2 years 3 months’) | 3 |
| date_trunc(text, timestamp) | timestamp | 截断成指定的精度 | date_trunc(‘hour’, timestamp ‘2001-02-16 20:38:40’) | 2001-02-16 20:00:00+00 |
| extract(field from timestamp) | double | 获取子域 | extract(hour from timestamp ‘2001-02-16 20:38:40’) | 20 |
| extract(field from interval) | double | 获取子域 | extract(month from interval ‘2 years 3 months’) | 3 |
| localtime | time | 今日的时间 | ||
| localtimestamp | timestamp | 日期和时间 | ||
| now() | timestamp | 当前的日期和时间(等效于 current_timestamp) | ||
| timeofday() | text | 当前日期和时间 |
3. EXTRACT，date_part函数支持的field：
| 域 | 描述 | 例子 | 结果 |
| CENTURY | 世纪 | EXTRACT(CENTURY FROM TIMESTAMP ‘2000-12-16 12:21:13’); | 20 |
| DAY | (月分)里的日期域(1-31) | EXTRACT(DAY from TIMESTAMP ‘2001-02-16 20:38:40’); | 16 |
| DECADE | 年份域除以10 | EXTRACT(DECADE from TIMESTAMP ‘2001-02-16 20:38:40’); | 200 |
| DOW | 每周的星期号(0-6；星期天是0) (仅用于timestamp) | EXTRACT(DOW FROM TIMESTAMP ‘2001-02-16 20:38:40’); | 5 |
| DOY | 一年的第几天(1 -365/366) (仅用于 timestamp) | EXTRACT(DOY from TIMESTAMP ‘2001-02-16 20:38:40’); | 47 |
| HOUR | 小时域(0-23) | EXTRACT(HOUR from TIMESTAMP ‘2001-02-16 20:38:40’); | 20 |
| MICROSECONDS | 秒域，包括小数部分，乘以 1,000,000。 | EXTRACT(MICROSECONDS from TIME ‘17:12:28.5’); | 28500000 |
| MILLENNIUM | 千年 | EXTRACT(MILLENNIUM from TIMESTAMP ‘2001-02-16 20:38:40’); | 3 |
| MILLISECONDS | 秒域，包括小数部分，乘以 1000。 | EXTRACT(MILLISECONDS from TIME ‘17:12:28.5’); | 28500 |
| MINUTE | 分钟域(0-59) | EXTRACT(MINUTE from TIMESTAMP ‘2001-02-16 20:38:40’); | 38 |
| MONTH | 对于timestamp数值，它是一年里的月份数(1-12)；对于interval数值，它是月的数目，然后对12取模(0-11) | EXTRACT(MONTH from TIMESTAMP ‘2001-02-16 20:38:40’); | 2 |
| QUARTER | 该天所在的该年的季度(1-4)(仅用于 timestamp) | EXTRACT(QUARTER from TIMESTAMP ‘2001-02-16 20:38:40’); | 1 |
| SECOND | 秒域，包括小数部分(0-59[1]) | EXTRACT(SECOND from TIMESTAMP ‘2001-02-16 20:38:40’); | 40 |
| WEEK | 该天在所在的年份里是第几周。 | EXTRACT(WEEK from TIMESTAMP ‘2001-02-16 20:38:40’); | 7 |
| YEAR | 年份域 | EXTRACT(YEAR from TIMESTAMP ‘2001-02-16 20:38:40’); | 2001 |
4. 当前日期/时间：
我们可以使用下面的函数获取当前的日期和/或时间∶
CURRENT_DATE
CURRENT_TIME
CURRENT_TIMESTAMP
CURRENT_TIME (precision)
CURRENT_TIMESTAMP (precision)
LOCALTIME
LOCALTIMESTAMP
LOCALTIME (precision)
LOCALTIMESTAMP (precision)
该博客中提供的所有信息均源自PostgreSQL官方文档，编写该篇博客的主要目的是便于今后的查阅，特此声明。
转载自http://www.cnblogs.com/stephen-liu74/archive/2012/05/04/2294643.html