PHP PDO::bindParam() data types.. how does it work?

In other DB abstraction frameworks in other languages it can be used for things like making sure you're doing the proper escaping for in-lining values (for drivers that don't support proper bound parameters) and improving network efficiency by making sure numbers are binary packed appropriately (given protocol support). It looks like in PDO, it doesn't do much.

   if (PDO_PARAM_TYPE(param->param_type) == PDO_PARAM_STR && param->max_value_len <= 0 && ! ZVAL_IS_NULL(param->parameter)) {                if (Z_TYPE_P(param->parameter) == IS_DOUBLE) {                        char *p;                        int len = spprintf(&p, 0, "%F", Z_DVAL_P(param->parameter));                        ZVAL_STRINGL(param->parameter, p, len, 0);                } else {                        convert_to_string(param->parameter);                }        } else if (PDO_PARAM_TYPE(param->param_type) == PDO_PARAM_INT && Z_TYPE_P(param->parameter) == IS_BOOL) {                convert_to_long(param->parameter);        } else if (PDO_PARAM_TYPE(param->param_type) == PDO_PARAM_BOOL && Z_TYPE_P(param->parameter) == IS_LONG) {                convert_to_boolean(param->parameter);        }

So, if you say it is a STR (or if you say nothing at all as that is the default) and your data's internal type is a double then it will turn it into a string using one method, if it's not a double then it will convert it to a string using a different method.

If you say it's an int but it is really a bool then it will convert it to a long.

If you say it's a bool but it's really a number then it will convert it to a true boolean.

This is really all I saw (quickly) looking at the stmt source, I imagine once you pass the parameters into the driver they can do additional magic. So, I'd guess that all you get is a little bit of do the right and a whole lot of behavior ambiguity and variance between drivers.

So I decided to dive into the PHP source code and this is what I found.

static int really_register_bound_param in ext/pdo/pdo_stmt.c on line 329 of version 5.2.9

if (PDO_PARAM_TYPE(param->param_type) == PDO_PARAM_STR && param->max_value_len <= 0 && ! ZVAL_IS_NULL(param->parameter)) {    if (Z_TYPE_P(param->parameter) == IS_DOUBLE) {        char *p;        int len = spprintf(&p, 0, "%F", Z_DVAL_P(param->parameter));        ZVAL_STRINGL(param->parameter, p, len, 0);    } else {        convert_to_string(param->parameter);    }} else if (PDO_PARAM_TYPE(param->param_type) == PDO_PARAM_INT && Z_TYPE_P(param->parameter) == IS_BOOL) {    convert_to_long(param->parameter);} else if (PDO_PARAM_TYPE(param->param_type) == PDO_PARAM_BOOL && Z_TYPE_P(param->parameter) == IS_LONG) {    convert_to_boolean(param->parameter);}

These are the conversions PDO does during binding.

• PDO::PARAM_STR converts whatever you give it to a string except null.
• PDO::PARAM_INT converts bools into longs
• PDO::PARAM_BOOL converts longs into bools

That's it. Nothing else is converted. PDO uses the PARAM flags to format SQL not to cast data types.

There's at least one effect PDO::PARAM_INT has on INSERT queries: boolean values are converted to 0 or 1. Like in

$i = true;$stmt->bindParam(':i', $v, PDO::PARAM_INT);

pdo_stmt.c:

else if (PDO_PARAM_TYPE(param->param_type) == PDO_PARAM_INT && Z_TYPE_P(param->parameter) == IS_BOOL) {        convert_to_long(param->parameter);}