Okay, here’s a comprehensive article on String Formatting in SQL Server using the FORMAT function, aiming for approximately 5000 words. This will be a deep dive, covering various aspects, nuances, and practical examples.
String Formatting in SQL Server with the FORMAT Function: A Comprehensive Guide
SQL Server provides various methods for manipulating and displaying data. One of the most powerful and versatile tools for controlling the presentation of data, particularly strings, dates, and numbers, is the FORMAT function. Introduced in SQL Server 2012, FORMAT offers a flexible and .NET-inspired approach to formatting, allowing developers to create highly customized output without resorting to complex string concatenation or numerous CONVERT calls.
This article will delve into the FORMAT function in detail, covering its syntax, capabilities, limitations, performance considerations, and practical examples. We’ll explore a wide range of formatting scenarios, from basic number and date formatting to advanced custom formats and culture-specific output.
1. Introduction to the FORMAT Function
The FORMAT function in SQL Server is designed to format a value according to a specified format string and, optionally, a culture. It’s conceptually similar to the String.Format method in .NET languages like C# and VB.NET. The function leverages the .NET Framework’s formatting capabilities, providing a consistent and predictable way to format data within SQL Server.
1.1. Basic Syntax
The basic syntax of the FORMAT function is as follows:
sql
FORMAT ( value, format [, culture ] )
value: The value to be formatted. This can be a column from a table, a variable, or a literal value. Supported data types include numeric types (int, bigint, smallint, tinyint, decimal, numeric, float, real, money, smallmoney), date and time types (date, datetime, datetime2, datetimeoffset, smalldatetime, time), and, in some cases, strings (althoughFORMATis primarily intended for numeric and date/time values).format: A string that specifies the desired format. This string uses standard .NET format specifiers, which we’ll explore in detail later. This is a required parameter.culture: (Optional) A string representing a culture code (e.g., ‘en-US’, ‘fr-FR’, ‘de-DE’). This determines the culture-specific formatting rules to be applied, such as date separators, decimal separators, currency symbols, and number grouping. If omitted, the current session’s culture is used.
1.2. Simple Examples
Let’s start with some basic examples to illustrate the function’s usage:
“`sql
— Format a number as currency (using the current session’s culture)
SELECT FORMAT(1234.56, ‘C’); — Output (en-US): $1,234.56
— Format a number as currency with a specific culture (French)
SELECT FORMAT(1234.56, ‘C’, ‘fr-FR’); — Output: 1 234,56 €
— Format a date in a standard short date format (using the current session’s culture)
SELECT FORMAT(GETDATE(), ‘d’); — Output (en-US): 11/15/2023 (Date may vary)
— Format a date in a standard long date format (using a specific culture – German)
SELECT FORMAT(GETDATE(), ‘D’, ‘de-DE’); — Output: Mittwoch, 15. November 2023 (Date may vary)
— Format a number with a fixed number of decimal places
SELECT FORMAT(123.4567, ‘N2’); — Output: 123.46
“`
These examples demonstrate the fundamental principle of FORMAT: providing a value and a format string to control the output. The real power of FORMAT comes from the wide range of format specifiers available.
2. Standard Numeric Format Strings
FORMAT supports a variety of standard numeric format strings, which are single-character codes that represent common formatting patterns. These format strings can often be followed by an optional precision specifier, which controls the number of digits or decimal places.
2.1. Common Numeric Format Specifiers
Here’s a table summarizing some of the most commonly used numeric format specifiers:
| Format Specifier | Description | Example (1234.567) | Example (0.1234) |
|---|---|---|---|
C or c |
Currency. Formats the number as currency, using the culture’s currency symbol, decimal separator, etc. | $1,234.57 (en-US) |
$0.12 (en-US) |
D or d |
Decimal. Formats an integer with leading zeros (if specified). Only works with integer types. | 1235 (D) |
N/A (integer only) |
E or e |
Exponential (scientific) notation. | 1.234567E+003 |
1.234000E-001 |
F or f |
Fixed-point. Formats the number with a fixed number of decimal places. | 1234.57 (F2) |
0.12 (F2) |
G or g |
General. Uses the most compact of either fixed-point or scientific notation. | 1234.567 |
0.1234 |
N or n |
Number. Formats the number with group separators (e.g., commas) and a fixed number of decimal places. | 1,234.57 (N2) |
0.12 (N2) |
P or p |
Percent. Multiplies the number by 100 and displays it as a percentage. | 123,456.70% (P1) |
12.34% (P2) |
X or x |
Hexadecimal. Formats an integer as a hexadecimal number. Only works with integer types. | 4D2 (X) |
N/A (integer only) |
R or r |
Round Trip. Format a floating number in the most precise way. | 1234.567 |
0.1234 |
2.2. Precision Specifiers
The precision specifier, which follows the format specifier, controls the number of digits or decimal places displayed. Its meaning varies slightly depending on the format specifier:
C,F,N,P: Specifies the number of decimal places.D: Specifies the minimum number of digits (leading zeros are added if necessary).E,G: Specifies the number of significant digits (total digits, not just after the decimal).R: No effect.X: Specifies the minimum number of digits (leading zeros are added if necessary).
2.3. Examples with Precision Specifiers
“`sql
— Currency with 4 decimal places
SELECT FORMAT(1234.56789, ‘C4’); — Output (en-US): $1,234.5679
— Fixed-point with 0 decimal places
SELECT FORMAT(1234.567, ‘F0’); — Output: 1235
— Number with 3 decimal places and group separators
SELECT FORMAT(1234567.89, ‘N3’); — Output: 1,234,567.890
— Percent with 1 decimal place
SELECT FORMAT(0.12345, ‘P1’); — Output: 12.3%
— Decimal with 5 digits (leading zeros)
SELECT FORMAT(123, ‘D5’); — Output: 00123
— Exponential with 2 significant digits
SELECT FORMAT(12345.67, ‘E2’); — Output: 1.2E+004
— Hexadecimal with 8 digits
SELECT FORMAT(255, ‘X8’); — Output: 000000FF
“`
3. Standard Date and Time Format Strings
FORMAT also provides a rich set of standard format strings for dates and times. These are single-character codes (case-sensitive) that represent common date and time patterns.
3.1. Common Date and Time Format Specifiers
| Format Specifier | Description | Example (2023-11-15 14:30:45.123) |
|---|---|---|
d |
Short date pattern. | 11/15/2023 (en-US) |
D |
Long date pattern. | Wednesday, November 15, 2023 (en-US) |
f |
Full date/time pattern (short time). | Wednesday, November 15, 2023 2:30 PM (en-US) |
F |
Full date/time pattern (long time). | Wednesday, November 15, 2023 2:30:45 PM (en-US) |
g |
General date/time pattern (short time). | 11/15/2023 2:30 PM (en-US) |
G |
General date/time pattern (long time). | 11/15/2023 2:30:45 PM (en-US) |
M or m |
Month/day pattern. | November 15 (en-US) |
O or o |
Round-trip (ISO 8601) date/time pattern. Culture-insensitive. | 2023-11-15T14:30:45.1230000 |
R or r |
RFC1123 pattern (GMT/UTC). | Wed, 15 Nov 2023 14:30:45 GMT |
s |
Sortable date/time pattern. Culture-insensitive. | 2023-11-15T14:30:45 |
t |
Short time pattern. | 2:30 PM (en-US) |
T |
Long time pattern. | 2:30:45 PM (en-US) |
u |
Universal sortable date/time pattern. | 2023-11-15 14:30:45Z |
U |
Universal full date/time pattern. | Wednesday, November 15, 2023 2:30:45 PM (en-US) |
Y or y |
Year/month pattern. | November 2023 (en-US) |
3.2. Key Differences and Considerations
- Case Sensitivity: Date and time format specifiers are case-sensitive.
d(short date) is different fromD(long date). - Culture Influence: Most date and time formats are culture-sensitive. The output will vary depending on the culture specified (or the session’s culture if none is specified).
Oands: TheO(round-trip) ands(sortable) formats are culture-insensitive and are recommended for storing or exchanging date/time values in a consistent format.Oincludes fractional seconds, whilesdoes not.R: TheR(RFC1123) format is always in GMT/UTC, regardless of the culture setting.U: The culture ofUformat is determined by the current setting, the string that displayed is in Coordinated Universal Time (UTC)
3.3. Examples with Different Cultures
“`sql
DECLARE @MyDate DATETIME2 = ‘2023-11-15 14:30:45.123’;
— Short date (en-US)
SELECT FORMAT(@MyDate, ‘d’, ‘en-US’); — Output: 11/15/2023
— Short date (fr-FR)
SELECT FORMAT(@MyDate, ‘d’, ‘fr-FR’); — Output: 15/11/2023
— Long date (de-DE)
SELECT FORMAT(@MyDate, ‘D’, ‘de-DE’); — Output: Mittwoch, 15. November 2023
— Long date (ja-JP)
SELECT FORMAT(@MyDate, ‘D’, ‘ja-JP’); — Output: 2023年11月15日
— Round-trip (ISO 8601) – culture-insensitive
SELECT FORMAT(@MyDate, ‘O’); — Output: 2023-11-15T14:30:45.1230000
— Short time (en-GB)
SELECT FORMAT(@MyDate, ‘t’, ‘en-GB’); — Output: 14:30
— Long time (es-ES)
SELECT FORMAT(@MyDate, ‘T’, ‘es-ES’); — Output: 14:30:45
“`
These examples demonstrate how the same date/time value can be displayed in significantly different ways depending on the format string and culture.
4. Custom Numeric Format Strings
While standard format strings cover many common scenarios, FORMAT also allows you to define custom numeric format strings. These strings provide fine-grained control over the appearance of numeric values, allowing you to specify:
- Digit placeholders
- Decimal and group separators
- Positive, negative, and zero value formatting
- Section separators
- Literal characters
4.1. Custom Numeric Format Specifiers
| Specifier | Description | Example (1234.56) | Example (-1234.56) | Example (0) |
|---|---|---|---|---|
0 |
Digit placeholder. Displays a digit or a zero if no digit is present. | 001234.56 (000000.00) |
-001234.56 (000000.00) |
000000.00 (000000.00) |
# |
Digit placeholder. Displays a digit if present; otherwise, nothing is displayed. | 1234.56 (####.##) |
-1234.56 (####.##) |
“ (####.##) |
. |
Decimal separator. The actual character used depends on the culture. | 1234.56 |
-1234.56 |
0.00 |
, |
Group separator (thousands separator). The actual character used depends on the culture. | 1,234.56 |
-1,234.56 |
0 |
% |
Percentage placeholder. Multiplies the value by 100 and displays it as a percentage. | 123456.00% |
-123456.00% |
0.00% |
‰ |
Per mille placeholder. Multiplies by 1000. | 1234560‰ |
-1234560‰ |
0‰ |
E0, E+0, e0, e+0 |
Scientific notation. | 1.23456E+03 |
-1.23456E+03 |
0.00000E+00 |
; |
Section separator. Separates formats for positive, negative, and zero values. | 1,234.56 (+#,##0.00;(#,##0.00);Zero) |
(1,234.56) (+#,##0.00;(#,##0.00);Zero) |
Zero (+#,##0.00;(#,##0.00);Zero) |
\ |
Escape character. Displays the next character literally. | \1234.56 (####.##) |
\-1234.56 (####.##) |
|
'...' or "..." |
Literal string. Displays the enclosed text literally. | Value: 1234.56 (‘Value: ‘ #,##0.00) |
Value: -1234.56 (‘Value: ‘ #,##0.00) |
4.2. Section Separators (;)
The semicolon (;) is crucial for defining different formats for positive, negative, and zero values. The format string is divided into up to three sections:
- Positive Format: Applied to positive values.
- Negative Format: Applied to negative values. If omitted, the positive format is used, and the negative sign is displayed.
- Zero Format: Applied to zero values. If omitted, the positive format is used.
4.3. Examples of Custom Numeric Formats
“`sql
— Basic custom format with digit placeholders
SELECT FORMAT(1234.567, ‘####.##’); — Output: 1234.57
— Leading zeros and fixed decimal places
SELECT FORMAT(12.34, ‘0000.00’); — Output: 0012.34
— Group separators and currency symbol
SELECT FORMAT(1234567.89, ‘$#,##0.00’); — Output: $1,234,567.89 (en-US)
— Different formats for positive, negative, and zero
SELECT FORMAT(1234.56, ‘#,##0.00;(#,##0.00);Zero’); — Output: 1,234.56
SELECT FORMAT(-1234.56, ‘#,##0.00;(#,##0.00);Zero’); — Output: (1,234.56)
SELECT FORMAT(0, ‘#,##0.00;(#,##0.00);Zero’); — Output: Zero
— Percentage with custom formatting
SELECT FORMAT(0.1234, ‘##.00%’); — Output: 12.34%
— Scientific notation with custom exponent format
SELECT FORMAT(1234567, ‘0.###E+00’); — Output: 1.235E+06
— Per mille example
SELECT FORMAT(0.005, ‘0.00‰’); — Output: 5.00‰
–Escaping Characters:
SELECT FORMAT (123, ‘###0’) — Output: #123
–Literal string:
SELECT FORMAT(1234.56, ‘”The value is: ” #,##0.00’) — Output: The value is: 1,234.56
— Combination of custom and standard parts
SELECT FORMAT (0.12, ‘This is #0.00\%’) –Output: This is 12.00%
“`
5. Custom Date and Time Format Strings
Similar to custom numeric formats, FORMAT allows you to define custom date and time format strings. This gives you precise control over how date and time components are displayed.
5.1. Custom Date and Time Format Specifiers
| Specifier | Description | Example (2023-11-15 14:30:45.123) |
|---|---|---|
d |
Day of the month (1-31). | 15 |
dd |
Day of the month (01-31). | 15 |
ddd |
Abbreviated day name (e.g., “Wed”). | Wed (en-US) |
dddd |
Full day name (e.g., “Wednesday”). | Wednesday (en-US) |
f to fffffff |
Fractional seconds (1 to 7 digits). | .1, .12, .123, etc. |
F to FFFFFFF |
Fractional seconds (1 to 7 digits), trailing zeros are omitted. | .1, .12, .123, etc. |
g, gg |
Period/era (e.g., “A.D.”). | A.D. (en-US) |
h |
Hour (1-12, 12-hour clock). | 2 |
hh |
Hour (01-12, 12-hour clock). | 02 |
H |
Hour (0-23, 24-hour clock). | 14 |
HH |
Hour (00-23, 24-hour clock). | 14 |
K |
Time zone information. | (Varies) |
m |
Minute (0-59). | 30 |
mm |
Minute (00-59). | 30 |
M |
Month (1-12). | 11 |
MM |
Month (01-12). | 11 |
MMM |
Abbreviated month name (e.g., “Nov”). | Nov (en-US) |
MMMM |
Full month name (e.g., “November”). | November (en-US) |
s |
Second (0-59). | 45 |
ss |
Second (00-59). | 45 |
t |
First character of AM/PM designator (e.g., “A” or “P”). | P (en-US) |
tt |
AM/PM designator (e.g., “AM” or “PM”). | PM (en-US) |
y |
Year (last digit). | 3 |
yy |
Year (last two digits). | 23 |
yyy |
Year (at least three digits, adding leading zeros if necessary). | 2023 |
yyyy |
Year (four digits). | 2023 |
yyyyy |
Year (at least five digits, adding leading zeros if necessary). | 02023 |
z |
Hours offset from UTC (-12 to +14). Displays sign only if non-zero. | (Varies) |
zz |
Hours offset from UTC (-12 to +14, with leading zero). Displays sign only if non-zero. | (Varies) |
zzz |
Full time zone offset (e.g., “-08:00”). | (Varies) |
: |
Time separator. The actual character used depends on the culture. | : (en-US) |
/ |
Date separator. The actual character used depends on the culture. | / (en-US) |
\ |
Escape character. | |
'...' or "..." |
Literal string. |
5.2. Key Differences and Considerations
* Case-Sensitivity: Just as with standard date and time formats, custom format specifiers are case-sensitive.
* f vs F: f specifiers always display the specified number of fractional second digits, padding with zeros if necessary. F specifiers display only the non-zero fractional second digits.
* K: The K specifier displays time zone information if the input value is a datetimeoffset type. It has no effect on other date/time types.
* z, zz, zzz: These specifiers also require a datetimeoffset input value to display time zone information.
5.3. Examples of Custom Date and Time Formats
“`sql
DECLARE @MyDateTime DATETIME2 = ‘2023-11-15 14:30:45.123’;
DECLARE @MyDateTimeOffset DATETIMEOFFSET = ‘2023-11-15 14:30:45.123 -08:00’;
— Custom date format
SELECT FORMAT(@MyDateTime, ‘yyyy-MM-dd’); — Output: 2023-11-15
— Custom date and time format
SELECT FORMAT(@MyDateTime, ‘MM/dd/yyyy hh:mm:ss tt’); — Output: 11/15/2023 02:30:45 PM (en-US)
— Abbreviated day and month
SELECT FORMAT(@MyDateTime, ‘ddd, MMM dd, yyyy’); — Output: Wed, Nov 15, 2023 (en-US)
— Fractional seconds
SELECT FORMAT(@MyDateTime, ‘yyyy-MM-dd HH:mm:ss.fff’); — Output: 2023-11-15 14:30:45.123
SELECT FORMAT(@MyDateTime, ‘yyyy-MM-dd HH:mm:ss.FFF’); — Output: 2023-11-15 14:30:45.123
— 12-hour clock with AM/PM
SELECT FORMAT(@MyDateTime, ‘hh:mm tt’); — Output: 02:30 PM (en-US)
— 24-hour clock
SELECT FORMAT(@MyDateTime, ‘HH:mm’); — Output: 14:30
— Time zone information (datetimeoffset)
SELECT FORMAT(@MyDateTimeOffset, ‘yyyy-MM-dd HH:mm:ss zzz’); — Output: 2023-11-15 14:30:45 -08:00
— Combining custom and literal characters
SELECT FORMAT(@MyDateTime, ‘The date is: dddd, MMMM dd, yyyy’); — Output: The date is: Wednesday, November 15, 2023 (en-US)
“`
6. Culture and Localization
The culture parameter in the FORMAT function is essential for producing localized output. It determines how date separators, time separators, decimal separators, group separators, currency symbols, and other culture-specific elements are displayed.
6.1. Culture Codes
Culture codes follow the IETF BCP 47 standard (also known as RFC 5646). A culture code typically consists of:
- Language code: A two-letter lowercase code representing the language (e.g., “en” for English, “fr” for French, “es” for Spanish).
- Region code: (Optional) A two-letter uppercase code representing a specific region or country (e.g., “US” for the United States, “GB” for Great Britain, “CA” for Canada).
Examples:
en-US: English (United States)en-GB: English (Great Britain)fr-FR: French (France)fr-CA: French (Canada)es-ES: Spanish (Spain)es-MX: Spanish (Mexico)de-DE: German (Germany)ja-JP: Japanese (Japan)zh-CN: Chinese (Simplified, China)zh-TW: Chinese (Traditional, Taiwan)
6.2. Determining the Current Session Culture
If you omit the culture parameter, FORMAT uses the current session’s culture. You can determine the current session culture using the following query:
sql
SELECT @@LANGUAGE;
Or
“`sql
SELECT sys.syslanguages.name
FROM sys.syslanguages
WHERE sys.syslanguages.lcid = @@LANGID;
“`
6.3. Setting the Session Culture
You can change the session’s culture using the SET LANGUAGE statement:
“`sql
SET LANGUAGE ‘French’; — Sets the session culture to French
SELECT FORMAT(1234.56, ‘C’); — Output: 1 234,56 € (now using French formatting)
SET LANGUAGE ‘us_english’; — Sets it back to US English.
“`
Important: SET LANGUAGE only affects the current session. It doesn’t change the server’s default language or other users’ sessions. If you need a persistent cultural setting, you’ll need to manage this at the application level or rely on user login settings.
6.4. Culture-Specific Examples
Let’s revisit some earlier examples and see how the culture affects the output:
“`sql
DECLARE @MyNumber DECIMAL(10,2) = 1234.56;
DECLARE @MyDate DATETIME = ‘2023-11-15 14:30:45’;
— Currency formatting
SELECT FORMAT(@MyNumber, ‘C’, ‘en-US’); — Output: $1,234.56
SELECT FORMAT(@MyNumber, ‘C’, ‘fr-FR’); — Output: 1 234,56 €
SELECT FORMAT(@MyNumber, ‘C’, ‘de-DE’); — Output: 1.234,56 €
SELECT FORMAT(@MyNumber, ‘C’, ‘ja-JP’); — Output: ￥1,235
— Short date formatting
SELECT FORMAT(@MyDate, ‘d’, ‘en-US’); — Output: 11/15/2023
SELECT FORMAT(@MyDate, ‘d’, ‘fr-FR’); — Output: 15/11/2023
SELECT FORMAT(@MyDate, ‘d’, ‘de-DE’); — Output: 15.11.2023
SELECT FORMAT(@MyDate, ‘d’, ‘ja-JP’); — Output: 2023/11/15
— Long date formatting
SELECT FORMAT(@MyDate, ‘D’, ‘en-US’); — Output: Wednesday, November 15, 2023
SELECT FORMAT(@MyDate, ‘D’, ‘fr-FR’); — Output: mercredi 15 novembre 2023
SELECT FORMAT(@MyDate, ‘D’, ‘de-DE’); — Output: Mittwoch, 15. November 2023
SELECT FORMAT(@MyDate, ‘D’, ‘ja-JP’); — Output: 2023年11月15日
— Custom date format with culture-specific separators
SELECT FORMAT(@MyDate, ‘dd/MM/yyyy’, ‘en-US’); — Output: 15/11/2023 (Uses /)
SELECT FORMAT(@MyDate, ‘dd/MM/yyyy’, ‘de-DE’); — Output: 15/11/2023 (Still uses /, because it’s in the format string)
SELECT FORMAT(@MyDate, ‘dd.MM.yyyy’, ‘de-DE’); — Output: 15.11.2023 (Uses .)
“`
6.5. The Invariant Culture
.NET provides a special culture called the “invariant culture” (represented by an empty string '' or the culture name InvariantCulture). The invariant culture is culture-neutral; it’s not associated with any particular language or region. It provides a consistent set of formatting rules that are independent of user or system settings. However, SQL Server does not fully support passing an empty string or 'InvariantCulture' as the culture parameter to FORMAT. It’s generally better to use an explicit culture code or rely on the session’s culture. If an empty string is passed in, the current language of the session is used.
7. Performance Considerations
While FORMAT is a powerful and convenient function, it’s significantly slower than using CONVERT with style codes or performing string concatenation. This is because FORMAT relies on the .NET Framework’s formatting engine, which involves overhead compared to the native SQL Server operations.
7.1. Benchmarking FORMAT vs. CONVERT
Here’s a simple benchmark demonstrating the performance difference:
“`sql
— Create a test table
CREATE TABLE #FormatTest (
ID INT IDENTITY(1,1) PRIMARY KEY,
MyDate DATETIME,
MyNumber DECIMAL(10,2)
);
— Insert some test data
INSERT INTO #FormatTest (MyDate, MyNumber)
SELECT GETDATE() – (CHECKSUM(NEWID()) % 1000), — Random dates within the last 1000 days
(CHECKSUM(NEWID()) % 100000) / 100.0 — Random numbers
FROM sys.objects s1
CROSS JOIN sys.objects s2; — Generate a large number of rows
— Test using FORMAT
SET STATISTICS TIME ON;
SELECT FORMAT(MyDate, ‘yyyy-MM-dd’), FORMAT(MyNumber, ‘C’)
FROM #FormatTest;
SET STATISTICS TIME OFF;
— Test using CONVERT
SET STATISTICS TIME ON;
SELECT CONVERT(VARCHAR, MyDate, 120), CONVERT(VARCHAR