How to Use the CONVERT() Function in SQL Server: A Complete Guide

The CONVERT() function converts a value (of any type) into a specified datatype.

Syntax:

CONVERT(data_type(length), expression, style)

Parameter Values

Value	Description
data_type	Required. The datatype to convert expression to. Can be one of the following: bigint, int, smallint, tinyint, bit, decimal, numeric, money, smallmoney, float, real, datetime, smalldatetime, char, varchar, text, nchar, nvarchar, ntext, binary, varbinary, or image
(length)	Optional. The length of the resulting data type (for char, varchar, nchar, nvarchar, binary and varbinary)
expression	Required. The value to convert to another data type
style	Optional. The format used to convert between data types, such as a date or string format. Can be one of the following values:

Converting datetime to character:

Without century	With century	Input/Output	Standard
0	100	mon dd yyyy hh:miAM/PM	Default
1	101	mm/dd/yyyy	US
2	102	yyyy.mm.dd	ANSI
3	103	dd/mm/yyyy	British/French
4	104	dd.mm.yyyy	German
5	105	dd-mm-yyyy	Italian
6	106	dd mon yyyy	-
7	107	Mon dd, yyyy	-
8	108	hh:mm:ss	-
9	109	mon dd yyyy hh:mi:ss:mmmAM (or PM)	Default + millisec
10	110	mm-dd-yyyy	USA
11	111	yyyy/mm/dd	Japan
12	112	yyyymmdd	ISO
13	113	dd mon yyyy hh:mi:ss:mmm	Europe (24 hour clock)>
14	114	hh:mi:ss:mmm	24 hour clock
20	120	yyyy-mm-dd hh:mi:ss	ODBC canonical (24 hour clock)
21	121	yyyy-mm-dd hh:mi:ss.mmm	ODBC canonical (24 hour clock)
	126	yyyy-mm-ddThh:mi:ss.mmm	ISO8601
	127	yyyy-mm-ddThh:mi:ss.mmmZ	ISO8601 (with time zone Z)
	130	dd mon yyyy hh:mi:ss:mmmAM	Hijiri
	131	dd/mm/yy hh:mi:ss:mmmAM	Hijiri

Converting float to real:

Value	Explanation
0	Maximum 6 digits (default)
1	8 digits
2	16 digits

Converting money to character:

Value	Explanation
0	No comma delimiters, 2 digits to the right of decimal
1	Comma delimiters, 2 digits to the right of decimal
2	No comma delimiters, 4 digits to the right of decimal

Code:

-- Convert an expression from one data type to another (varchar):
SELECT CONVERT(varchar, 25.65);

-- Convert an expression from one data type to another (datetime):
SELECT CONVERT(datetime, '2017-08-25');

--Convert an expression from one data type to another (varchar):
SELECT CONVERT(varchar, '2017-08-25', 101);

Output:

The above code will produce the following result-

25.65
2017-08-25 00:00:00.000
2017-08-25

Consider the Employees Table below

The following queries convert, DateOfBirth's DateTime datatype to NVARCHAR.

Code:

Select Id, Name, DOB, Convert(nvarchar, DOB, 103) as ConvertedDOB
from Employee

Prerequisite Code:

Drop table Employee

Create Table Employee(
 Id int NOT NULL primary key,
 Name nvarchar(50),
 DOB datetime
)

insert into Employee values ('1', 'Rambo', '1986-11-14 08:26:00.000')
insert into Employee values ('2', 'Azam', '1984-10-10 03:32:00.000')
insert into Employee values ('3', 'Inza', '1996-07-26 08:26:00.000')
insert into Employee values ('4', 'Jaman', '1990-11-02 03:32:00.000')
insert into Employee values ('5', 'Asad', '1991-01-03 03:32:00.000')
insert into Employee values ('6', 'kamran', '1990-11-02 03:32:00.000')

Select * from Employee