How to get the size of a varchar[n] field in one S

问题:

Suppose that I have a SQL table that has a varchar[1000] field called "Remarks".

I would like to craft a single SQL statement, which when executed, will return 1000, or whatever the size of the varchar field might be changed to in the future.

Something like SELECT size(Remarks) FROM mytable.

How do I do this?

回答1:

select column_name, data_type, character_maximum_length    
  from information_schema.columns  
 where table_name = 'myTable'

回答2:

On SQL Server specifically:

SELECT DATALENGTH(Remarks) AS FIELDSIZE FROM mytable

Documentation

回答3:

For SQL Server (2008 and above):

SELECT COLUMNPROPERTY(OBJECT_ID('mytable'), 'Remarks', 'PRECISION');

COLUMNPROPERTY returns information for a column or parameter (id, column/parameter, property). The PRECISION property returns the length of the data type of the column or parameter.

COLUMNPROPERTY documentation

回答4:

This will work on SQL SERVER...

SELECT COL_LENGTH('Table', 'Column')

回答5:

I was looking for the TOTAL size of the column and hit this article, my solution is based off of MarcE's.

SELECT sum(DATALENGTH(your_field)) AS FIELDSIZE FROM your_table

回答6:

Where is a function for calculating max valid length for varchar(Nn):

CREATE FUNCTION [dbo].[GetMaxVarcharColumnLength] (@TableSchema NVARCHAR(MAX), @TableName NVARCHAR(MAX), @ColumnName VARCHAR(MAX))
RETURNS INT
AS
BEGIN
    RETURN (SELECT character_maximum_length FROM information_schema.columns  
            WHERE table_schema = @TableSchema AND table_name = @TableName AND column_name = @ColumnName);
END

Usage:

IF LEN(@Name) > [dbo].[GetMaxVarcharColumnLength]('person', 'FamilyStateName', 'Name') 
            RETURN [dbo].[err_Internal_StringForVarcharTooLong]();

回答7:

For t-SQL I use the following query for varchar columns (shows the collation and is_null properties):

SELECT
    s.name
    , o.name as table_name
    , c.name as column_name
    , t.name as type
    , c.max_length
    , c.collation_name
    , c.is_nullable
FROM
    sys.columns c
    INNER JOIN sys.objects o ON (o.object_id = c.object_id)
    INNER JOIN sys.schemas s ON (s.schema_id = o.schema_id)
    INNER JOIN sys.types t ON (t.user_type_id = c.user_type_id)
WHERE
    s.name = 'dbo'
    AND t.name IN ('varchar') -- , 'char', 'nvarchar', 'nchar')
ORDER BY
    o.name, c.name

回答8:

select column_name, data_type, character_maximum_length    
from INFORMATION_SCHEMA.COLUMNS
where table_name = 'Table1'