SQL SERVER: String or binary data would be truncated. nvarchar

Question

I'm trying to insert into the following table:

but for some reason I cannot insert more than 250 characters into slabel1 field, even though it's size it's 500. Every time this happens I receive the following error:

String or binary data would be truncated. The statement has been terminated.

I do not understand why.

Answer 1

Your results show the length in bytes of the column, not how many characters it can store. The column you are using is an nvarchar column, and so a character will take up 2 bytes instead of 1, so in your case (500 / 2) = 250 characters max.

This will show you the difference, we have two columns, each which can hold 50 characters, but the length of the nvarchar column is 100

CREATE TABLE [#text]
(
  [Text] VARCHAR(50),
  [NText] NVARCHAR(50)
)

SELECT COL_LENGTH( 'tempdb..#Text' , 'Text' ) [Varchar_Length],
       COL_LENGTH( 'tempdb..#Text' , 'NText' ) [NVarchar_Length]


DROP TABLE [#text]

The results are:

Varchar_Length | NVarchar_Length
50             | 100

Answer 2

Because it's NVARCHAR

nchar and nvarchar

nchar [ ( n ) ]

Fixed-length Unicode string data. n defines the string length and must be a value from 1 through 4,000. The storage size is two times n bytes. When the collation code page uses double-byte characters, the storage size is still n bytes. Depending on the string, the storage size of n bytes can be less than the value specified for n. The ISO synonyms for nchar are national char and national character..

nvarchar [ ( n | max ) ]

Variable-length Unicode string data. n defines the string length and can be a value from 1 through 4,000. max indicates that the maximum storage size is 2^31-1 bytes (2 GB). The storage size, in bytes, is two times the actual length of data entered + 2 bytes. The ISO synonyms for nvarchar are national char varying and national character varying.

Try this one to see the differences

DECLARE @text1 NVARCHAR(200)
DECLARE @text2 VARCHAR(200)

SET @text1 = 'aaaaaaaa'
SET @text2 = 'aaaaaaaa'

SELECT LEN(@text1), DATALENGTH(@text1)

SELECT LEN(@text2), DATALENGTH(@text2)