6.7. Data Type Formatting Functions

The PostgreSQL formatting functions provide a powerful set of tools for converting various data types (date/time, integer, floating point, numeric) to formatted strings and for converting from formatted strings to specific data types. Table 6-12 lists them. These functions all follow a common calling convention: the first argument is the value to be formatted and the second argument is a template that defines the output or input format.

In an output template string, there are certain patterns that are recognized and replaced with appropriately-formatted data from the value to be formatted. Any text that is not a template pattern is simply copied verbatim. Similarly, in an input template string, template patterns identify the parts of the input data string to be looked at and the values to be found there.

Table 6-13 shows the template patterns available for formatting date and time values.

Certain modifiers may be applied to any template pattern to alter its behavior. For example, "FMMonth" is the "Month" pattern with the "FM" prefix. Table 6-14 shows the modifier patterns for date/time formatting.

Usage notes for the date/time formatting:

• FM suppresses leading zeroes and trailing blanks that would otherwise be added to make the output of a pattern be fixed-width.

• to_timestamp and to_date skip multiple blank spaces in the input string if the FX option is not used. FX must be specified as the first item in the template; for example to_timestamp('2000 JUN','YYYY MON') is right, but to_timestamp('2000 JUN','FXYYYY MON') returns an error, because to_timestamp expects one blank space only.

• If a backslash ("\") is desired in a string constant, a double backslash ("\\") must be entered; for example '\\HH\\MI\\SS'. This is true for any string constant in PostgreSQL.

• Ordinary text is allowed in to_char templates 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 pattern keywords. For example, in '"Hello Year "YYYY', the YYYY will be replaced by the year data, but the single Y in "Year" will not be.

• If you want to have a double quote in the output you must precede it with a backslash, for example '\\"YYYY Month\\"'.

• YYYY conversion from string to timestamp or date is restricted if you use a year 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 year 20000): to_date('200001131', 'YYYYMMDD') will be interpreted as a 4-digit year; better is to use a non-digit separator after the year, like to_date('20000-1131', 'YYYY-MMDD') or to_date('20000Nov31', 'YYYYMonDD').

• Millisecond MS and microsecond US values in a conversion from string to time stamp are used as part of the seconds after the decimal point. For example to_timestamp('12:3', 'SS:MS') is not 3 milliseconds, but 300, because the conversion counts it as 12 + 0.3. This means for the format SS:MS, the input values 12:3, 12:30, and 12:300 specify the same number of milliseconds. To get three milliseconds, one must use 12:003, which the conversion counts as 12 + 0.003 = 12.003 seconds.

  Here is a more complex example: to_timestamp('15:12:02.020.001230','HH:MI:SS.MS.US') is 15 hours, 12 minutes, and 2 seconds + 20 milliseconds + 1230 microseconds = 2.021230 seconds.

Table 6-15 shows the template patterns available for formatting numeric values.

Usage notes for the numeric formatting:

• A sign formatted using SG, PL, or MI is not an anchor in the number; for example, to_char(-12, 'S9999') produces ' -12', but to_char(-12, 'MI9999') produces '- 12'. The Oracle implementation does not allow the use of MI ahead of 9, but rather requires that 9 precede MI.

• 9 specifies a value with the same number of digits as there are 9s. If a digit is not available it outputs a space.

• TH does not convert values less than zero and does not convert decimal numbers.

• PL, SG, and TH are PostgreSQL extensions.

• V effectively multiplies the input values by 10^n, where n is the number of digits following V. to_char does not support the use of V combined with a decimal point. (E.g., 99.9V99 is not allowed.)

Table 6-16 shows some examples of the use of the to_char function.