Why does SQL INSERT only save the first character?

The Problem Where SQL INSERT Saves Only the First Character Instead of the Full Value

The problem where an SQL INSERT command saves only the first character instead of the full value most commonly occurs due to incorrect specification of varchar parameter lengths in stored procedures or when passing parameters from an application. This happens because in SQL Server, when no length is specified for varchar parameters, a default value of 1 is used.

Contents

• Main Causes of the Problem
• Solution for Stored Procedures
• Issues with Application Parameters
• Checking Table Structure
• Diagnosis and Debugging

Main Causes of the Problem

The most common reasons for only the first character being saved in the database are:

1. Not specifying parameter lengths in stored procedures

As noted in the official Microsoft documentation, “When n isn’t specified in a data definition or variable declaration statement, the default length is 1.”

This means that if you declare a parameter as varchar without specifying a length, SQL Server automatically uses a length of 1 character:

-- WRONG - only the first character will be stored
CREATE PROCEDURE InsertUser (@FirstName varchar)

2. Issues with parameter binding in application code

In applications written in PHP and other languages, there can be problems with proper parameter binding. For example, one discussion on Stack Overflow shows a problem with mysqli where parameters are not properly bound.

3. Errors in computed columns

Sometimes the issue is related to computed columns that use LEFT or SUBSTRING functions with incorrect parameters. As shown in a discussion on DBA StackExchange, this can cause “Invalid length parameter passed to the LEFT or SUBSTRING function” errors.

Solution for Stored Procedures

To fix the issue in stored procedures, always specify an explicit length for varchar parameters:

Correct Parameter Declaration

-- CORRECT - specifying explicit length
CREATE PROCEDURE InsertUser
    @FirstName varchar(255),
    @LastName varchar(255),
    @City varchar(100)
AS
BEGIN
    INSERT INTO public.user (user_name, last_name, city)
    VALUES (@FirstName, @LastName, @City)
END

Why This Matters

As experts explain on StackOverflow, “Then the length is ‘1’ by default. You can easily fix this by adding a length.”

Issues with Application Parameters

If the issue occurs when inserting data from an application, check the following aspects:

1. Correct Parameter Binding

Ensure that your code correctly specifies parameter types and lengths. For example, for PHP with mysqli:

// Correct parameter binding with type specification
$stmt = mysqli_prepare($link, "INSERT INTO public.user (user_name, last_name, city) VALUES (?,?,?)");
mysqli_stmt_bind_param($stmt, 'sss', $user_name, $last_name, $city);

2. Data Validation Before Insertion

Add data validation before performing INSERT:

-- Data validation before insertion
SELECT LEN(@test_param) AS length_check;

Checking Table Structure

Sometimes the issue may be related to the structure of the table itself:

1. Checking Column Types

Ensure that the column types in the table can store the expected data:

-- Checking table structure
SELECT column_name, data_type, character_maximum_length
FROM information_schema.columns
WHERE table_name = 'user';

2. Length Constraints

If a column has a length constraint, exceeding values will be truncated:

-- Example of a column with length constraint
ALTER TABLE public.user ALTER COLUMN user_name VARCHAR(50);

Diagnosis and Debugging

To diagnose the problem, use the following approaches:

1. Step-by-Step Verification

Execute queries step by step to determine the exact cause:

-- Checking parameters before insertion
DECLARE @test_name varchar(255) = 'names';
SELECT @test_name AS test_value, LEN(@test_name) AS length;

-- Checking insertion with explicit values
INSERT INTO public.user (user_name, last_name, city) 
VALUES ('names', 'lastname', 'city');

-- Checking the result
SELECT * FROM public.user;

2. Error Logging

Add error handling to get additional information:

BEGIN TRY
    INSERT INTO public.user (user_name, last_name, city) 
    VALUES ('names', 'lastname', 'city');
END TRY
BEGIN CATCH
    SELECT 
        ERROR_NUMBER() AS ErrorNumber,
        ERROR_MESSAGE() AS ErrorMessage;
END CATCH

3. Using a Debugger

For complex cases, use the SQL Server debugger or your application’s tools to track parameter values at each stage of execution.

Sources

1. Microsoft Learn - char and varchar (Transact-SQL)
2. StackOverflow - SQL Insert Only First Letter
3. DBA StackExchange - Invalid length parameter passed to the LEFT or SUBSTRING function when inserting
4. StackOverflow - Why my procedure insert just first character from string?
5. StackOverflow - MySQL inserts only first character

Conclusion

The main reasons why SQL INSERT saves only the first character are:

1. Not specifying parameter lengths - always use varchar(n) with an explicit length
2. Incorrect parameter binding in applications - ensure proper data type specification
3. Table structure constraints - check the types and lengths of columns in the target table
4. Issues with computed columns - verify the correctness of SUBSTRING and LEFT functions

To resolve the problem, it is recommended to:

• Always specify explicit lengths for varchar parameters in stored procedures
• Add data validation before performing INSERT
• Use debugging to track parameter values
• Verify that the target table structure matches the expected data

By following these recommendations, you can avoid the problem of saving only the first character instead of the full value in the database.