Why Does Inserting 0 into a MySQL BIT(1) Field Result in 1?

Inserting 0 into a MySQL BIT(1) Field Results in 1: Problem and Solution

An attempt to insert a 0 value into a BIT(1) field in MySQL using PDO prepared statements unexpectedly results in a value of 1 being written to the table. This behavior occurs despite using various forms of parameter binding and even raw SQL, but only when inserting the value 0.

Why Placeholders Fail for 0 Insertion

The BIT column in MySQL is a binary type, which may cause compatibility issues with client libraries like PDO. The problem arises due to the following reasons:

• BIT columns are byte-aligned, consuming a full byte for each row, regardless of the specified size.
• PDO incorrectly interprets the 0 value as a bit 1 due to byte alignment issues.

Solution: Use TINYINT(1) Instead

To resolve this issue, it is recommended to modify the column type from BIT(1) to TINYINT(1). This will ensure that a single byte is allocated for each row, regardless of the inserted value. TINYINT(1) can also be used to store boolean values, eliminating the compatibility issues with BIT columns.

For example, the following code should work correctly:

$pdo = new PDO("connection string etc") ;
$statement = $pdo->prepare('INSERT INTO `test` (SomeText,TestBool) VALUES (?,?)') ;
$statement->execute(array("TEST",0)) ;

If you still want to use BIT(1), you can attempt the following workaround:

$statement = $pdo->prepare('INSERT INTO `test` (SomeText,TestBool) VALUES (:someText,:testBool)') ;
$statement->bindValue(':someText', "TEST");
$statement->bindValue(':testBool', 0, PDO::PARAM_INT);
$statement->execute();

However, switching to TINYINT(1) is the preferred solution as it provides consistent behavior across different data types and ensures compatibility with various client libraries.

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