tsql-functions

name	tsql-functions
description	Complete T-SQL function reference for SQL Server and Azure SQL Database. Use this skill when: (1) User asks about T-SQL string, date, math, or conversion functions, (2) User needs help with window/ranking functions, (3) User works with JSON or XML in T-SQL, (4) User asks about aggregate functions or GROUP BY, (5) User needs system or metadata functions.

T-SQL Functions Reference

Complete reference for all T-SQL function categories with version-specific availability.

Quick Reference

String Functions

Function	Description	Version
CONCAT(str1, str2, ...)	NULL-safe concatenation	2012+
CONCAT_WS(sep, str1, ...)	Concatenate with separator	2017+
STRING_AGG(expr, sep)	Aggregate strings	2017+
STRING_SPLIT(str, sep)	Split to rows	2016+
STRING_SPLIT(str, sep, 1)	With ordinal column	2022+
TRIM([chars FROM] str)	Remove leading/trailing	2017+
TRANSLATE(str, from, to)	Character replacement	2017+
FORMAT(value, format)	.NET format strings	2012+

Date/Time Functions

Function	Description	Version
DATEADD(part, n, date)	Add interval	All
DATEDIFF(part, start, end)	Difference (int)	All
DATEDIFF_BIG(part, s, e)	Difference (bigint)	2016+
EOMONTH(date, [offset])	Last day of month	2012+
DATETRUNC(part, date)	Truncate to precision	2022+
DATE_BUCKET(part, n, date)	Group into buckets	2022+
AT TIME ZONE 'tz'	Timezone conversion	2016+

Window Functions

Function	Description	Version
ROW_NUMBER()	Sequential unique numbers	2005+
RANK()	Rank with gaps for ties	2005+
DENSE_RANK()	Rank without gaps	2005+
NTILE(n)	Distribute into n groups	2005+
LAG(col, n, default)	Previous row value	2012+
LEAD(col, n, default)	Next row value	2012+
FIRST_VALUE(col)	First in window	2012+
LAST_VALUE(col)	Last in window	2012+
IGNORE NULLS	Skip NULLs in offset funcs	2022+

SQL Server 2022 New Functions

Function	Description
GREATEST(v1, v2, ...)	Maximum of values
LEAST(v1, v2, ...)	Minimum of values
DATETRUNC(part, date)	Truncate date
GENERATE_SERIES(start, stop, [step])	Number sequence
JSON_OBJECT('key': val)	Create JSON object
JSON_ARRAY(v1, v2, ...)	Create JSON array
JSON_PATH_EXISTS(json, path)	Check path exists
IS [NOT] DISTINCT FROM	NULL-safe comparison

Core Patterns

String Manipulation

-- Concatenate with separator (NULL-safe)
SELECT CONCAT_WS(', ', FirstName, MiddleName, LastName) AS FullName

-- Split string to rows with ordinal
SELECT value, ordinal
FROM STRING_SPLIT('apple,banana,cherry', ',', 1)

-- Aggregate strings with ordering
SELECT DeptID,
       STRING_AGG(EmployeeName, ', ') WITHIN GROUP (ORDER BY HireDate)
FROM Employees
GROUP BY DeptID

Date Operations

-- Truncate to first of month
SELECT DATETRUNC(month, OrderDate) AS MonthStart

-- Group by week buckets
SELECT DATE_BUCKET(week, 1, OrderDate) AS WeekBucket,
       COUNT(*) AS OrderCount
FROM Orders
GROUP BY DATE_BUCKET(week, 1, OrderDate)

-- Generate date series
SELECT CAST(value AS date) AS Date
FROM GENERATE_SERIES(
    CAST('2024-01-01' AS date),
    CAST('2024-12-31' AS date),
    1
)

Window Functions

-- Running total with partitioning
SELECT OrderID, CustomerID, Amount,
       SUM(Amount) OVER (
           PARTITION BY CustomerID
           ORDER BY OrderDate
           ROWS UNBOUNDED PRECEDING
       ) AS RunningTotal
FROM Orders

-- Get previous non-NULL value (SQL 2022+)
SELECT Date, Value,
       LAST_VALUE(Value) IGNORE NULLS OVER (
           ORDER BY Date
           ROWS BETWEEN UNBOUNDED PRECEDING AND 1 PRECEDING
       ) AS PreviousNonNull
FROM Measurements

JSON Operations

-- Extract scalar value
SELECT JSON_VALUE(JsonColumn, '$.customer.name') AS CustomerName

-- Parse JSON array to rows
SELECT j.ProductID, j.Quantity
FROM Orders
CROSS APPLY OPENJSON(OrderDetails)
WITH (
    ProductID INT '$.productId',
    Quantity INT '$.qty'
) AS j

-- Build JSON object (SQL 2022+)
SELECT JSON_OBJECT('id': CustomerID, 'name': CustomerName) AS CustomerJson
FROM Customers

Additional References

For deeper coverage of specific function categories, see:

• references/string-functions.md - Complete string function reference with examples
• references/window-functions.md - Window and ranking functions with frame specifications