tsql-functions

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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.

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T-SQL Functions Reference

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

Quick Reference

String Functions

FunctionDescriptionVersion
CONCAT(str1, str2, ...)
NULL-safe concatenation2012+
CONCAT_WS(sep, str1, ...)
Concatenate with separator2017+
STRING_AGG(expr, sep)
Aggregate strings2017+
STRING_SPLIT(str, sep)
Split to rows2016+
STRING_SPLIT(str, sep, 1)
With ordinal column2022+
TRIM([chars FROM] str)
Remove leading/trailing2017+
TRANSLATE(str, from, to)
Character replacement2017+
FORMAT(value, format)
.NET format strings2012+

Date/Time Functions

FunctionDescriptionVersion
DATEADD(part, n, date)
Add intervalAll
DATEDIFF(part, start, end)
Difference (int)All
DATEDIFF_BIG(part, s, e)
Difference (bigint)2016+
EOMONTH(date, [offset])
Last day of month2012+
DATETRUNC(part, date)
Truncate to precision2022+
DATE_BUCKET(part, n, date)
Group into buckets2022+
AT TIME ZONE 'tz'
Timezone conversion2016+

Window Functions

FunctionDescriptionVersion
ROW_NUMBER()
Sequential unique numbers2005+
RANK()
Rank with gaps for ties2005+
DENSE_RANK()
Rank without gaps2005+
NTILE(n)
Distribute into n groups2005+
LAG(col, n, default)
Previous row value2012+
LEAD(col, n, default)
Next row value2012+
FIRST_VALUE(col)
First in window2012+
LAST_VALUE(col)
Last in window2012+
IGNORE NULLS
Skip NULLs in offset funcs2022+

SQL Server 2022 New Functions

FunctionDescription
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

sql
-- 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

sql
-- 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

sql
-- 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

sql
-- 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