小技巧 存在有 to_timestamp 和 to_date 來處理無法透過簡單轉換進行轉換的輸入格式。對於大多數標準日期/時間格式，只需將來源字串強制轉換為所需的資料型別即可，並且非常容易。同樣地，對於標準數字表示形式，to_number 也不是必要的。
在 to_char 輸出樣版字串中，基於給予值識別並替換為某些格式資料的某些樣式。 非樣板的任何文字都將被逐字複製。同樣地，在輸入樣板字串（用於其他功能）中，樣板標識輸入資料字串要提供的值。如果樣板字串中存在不是樣板的字串，則只需跳過輸入資料字串中的相對應字元（無論它們是否等於樣板字串字元）。
Modifiers can be applied to any template pattern to alter its behavior. For example,
Monthpattern with the
FMmodifier. Table 9.26 shows the modifier patterns for date/time formatting.
Usage notes for date/time formatting:
FMsuppresses leading zeroes and trailing blanks that would otherwise be added to make the output of a pattern be fixed-width. In PostgreSQL,
FMmodifies only the next specification, while in Oracle
FMaffects all subsequent specifications, and repeated
FMmodifiers toggle fill mode on and off.
TMdoes not include trailing blanks.
to_dateskip multiple blank spaces at the beginning of the input string and around date and time values unless the
FXoption is used. For example,
to_timestamp(' 2000 JUN', 'YYYY MON')and
to_timestamp('2000 - JUN', 'YYYY-MON')work, but
to_timestamp('2000 JUN', 'FXYYYY MON')returns an error because
to_timestampexpects only a single space.
FXmust be specified as the first item in the template.
- A separator (a space or non-letter/non-digit character) in the template string of
to_datematches any single separator in the input string or is skipped, unless the
FXoption is used. For example,
to_timestamp('2000/JUN', 'YYYY MON')work, but
to_timestamp('2000//JUN', 'YYYY/MON')returns an error because the number of separators in the input string exceeds the number of separators in the template.If
FXis specified, a separator in the template string matches exactly one character in the input string. But note that the input string character is not required to be the same as the separator from the template string. For example,
to_timestamp('2000/JUN', 'FXYYYY MON')works, but
to_timestamp('2000/JUN', 'FXYYYY MON')returns an error because the second space in the template string consumes the letter
Jfrom the input string.
TZHtemplate pattern can match a signed number. Without the
FXoption, minus signs may be ambiguous, and could be interpreted as a separator. This ambiguity is resolved as follows: If the number of separators before
TZHin the template string is less than the number of separators before the minus sign in the input string, the minus sign is interpreted as part of
TZH. Otherwise, the minus sign is considered to be a separator between values. For example,
to_timestamp('2000 -10', 'YYYY TZH')matches
to_timestamp('2000 -10', 'YYYY TZH')matches
- Ordinary text is allowed in
to_chartemplates and will be output literally. You can put a substring in double quotes to force it to be interpreted as literal text even if it contains template patterns. For example, in
'"Hello Year "YYYY', the
YYYYwill be replaced by the year data, but the single
Yearwill not be. In
to_timestamp, literal text and double-quoted strings result in skipping the number of characters contained in the string; for example
"XX"skips two input characters (whether or not they are
XX).TipPrior to PostgreSQL 12, it was possible to skip arbitrary text in the input string using non-letter or non-digit characters. For example,
to_timestamp('2000y6m1d', 'yyyy-MM-DD')used to work. Now you can only use letter characters for this purpose. For example,
- If you want to have a double quote in the output you must precede it with a backslash, for example
'\"YYYY Month\"'. Backslashes are not otherwise special outside of double-quoted strings. Within a double-quoted string, a backslash causes the next character to be taken literally, whatever it is (but this has no special effect unless the next character is a double quote or another backslash).
to_date, if the year format specification is less than four digits, e.g.
YYY, and the supplied year is less than four digits, the year will be adjusted to be nearest to the year 2020, e.g.
YYYYconversion has a restriction when processing years with more than 4 digits. You must use some non-digit character or template after
YYYY, otherwise the year is always interpreted as 4 digits. For example (with the year 20000):
to_date('200001131', 'YYYYMMDD')will be interpreted as a 4-digit year; instead use a non-digit separator after the year, like
CC(century) field is accepted but ignored if there is a
CCis used with
Ythen the result is computed as that year in the specified century. If the century is specified but the year is not, the first year of the century is assumed.
to_date, weekday names or numbers (
D, and related field types) are accepted but are ignored for purposes of computing the result. The same is true for quarter (
to_date, an ISO 8601 week-numbering date (as distinct from a Gregorian date) can be specified in one of two ways:
Attempting to enter a date using a mixture of ISO 8601 week-numbering fields and Gregorian date fields is nonsensical, and will cause an error. In the context of an ISO 8601 week-numbering year, the concept of a “month” or “day of month” has no meaning. In the context of a Gregorian year, the ISO week has no meaning.CautionWhile
- Year, week number, and weekday: for example
to_date('2006-42-4', 'IYYY-IW-ID')returns the date
2006-10-19. If you omit the weekday it is assumed to be 1 (Monday).
- Year and day of year: for example
to_date('2006-291', 'IYYY-IDDD')also returns
to_datewill reject a mixture of Gregorian and ISO week-numbering date fields,
to_charwill not, since output format specifications like
YYYY-MM-DD (IYYY-IDDD)can be useful. But avoid writing something like
IYYY-MM-DD; that would yield surprising results near the start of the year. (See Section 9.9.1 for more information.)
to_timestamp, millisecond (
MS) or microsecond (
US) fields are used as the seconds digits after the decimal point. For example
to_timestamp('12.3', 'SS.MS')is not 3 milliseconds, but 300, because the conversion treats it as 12 + 0.3 seconds. So, for the format
SS.MS, the input values
12.300specify the same number of milliseconds. To get three milliseconds, one must write
12.003, which the conversion treats as 12 + 0.003 = 12.003 seconds.Here is a more complex example:
to_timestamp('15:12:02.020.001230', 'HH24:MI:SS.MS.US')is 15 hours, 12 minutes, and 2 seconds + 20 milliseconds + 1230 microseconds = 2.021230 seconds.
to_char(..., 'ID')'s day of the week numbering matches the
extract(isodow from ...)function, but
to_char(..., 'D')'s does not match
extract(dow from ...)'s day numbering.
HH12as shown on a 12-hour clock, for example zero hours and 36 hours both output as
HH24outputs the full hour value, which can exceed 23 in an
Usage notes for numeric formatting:
0specifies a digit position that will always be printed, even if it contains a leading/trailing zero.
9also specifies a digit position, but if it is a leading zero then it will be replaced by a space, while if it is a trailing zero and fill mode is specified then it will be deleted. (For
to_number(), these two pattern characters are equivalent.)
- The pattern characters
Grepresent the sign, currency symbol, decimal point, and thousands separator characters defined by the current locale (see lc_monetary and lc_numeric). The pattern characters period and comma represent those exact characters, with the meanings of decimal point and thousands separator, regardless of locale.
- If no explicit provision is made for a sign in
to_char()'s pattern, one column will be reserved for the sign, and it will be anchored to (appear just left of) the number. If
Sappears just left of some
9's, it will likewise be anchored to the number.
- A sign formatted using
MIis not anchored to the number; for example,
' -12'. (The Oracle implementation does not allow the use of
9, but rather requires that
THdoes not convert values less than zero and does not convert fractional numbers.
THare PostgreSQL extensions.
to_number, if non-data template patterns such as
THare used, the corresponding number of input characters are skipped, whether or not they match the template pattern, unless they are data characters (that is, digits, sign, decimal point, or comma). For example,
THwould skip two non-data characters.
to_charmultiplies the input values by
nis the number of digits following
to_numberdivides in a similar manner.
to_numberdo not support the use of
Vcombined with a decimal point (e.g.,
99.9V99is not allowed).
EEEE(scientific notation) cannot be used in combination with any of the other formatting patterns or modifiers other than digit and decimal point patterns, and must be at the end of the format string (e.g.,
9.99EEEEis a valid pattern).
Certain modifiers can be applied to any template pattern to alter its behavior. For example,
99.99pattern with the
FMmodifier. Table 9.28 shows the modifier patterns for numeric formatting.