MySQL HY093: what “Invalid parameter number” actually means
HY093 usually means the SQL placeholders and bound values do not match. The fastest fix is to compare the final SQL contract, not stare at the exception.
Translate the exception
PDO uses placeholders so SQL and values can be handled separately. HY093 often appears when the query contains a different number or set of placeholders than the values supplied to execute(), or when a named placeholder is missing, misspelled or reused in a way the driver does not support.
The error may surface far away from where the query string was built, especially when filters are assembled dynamically.
Count the final placeholders
Log or inspect the final SQL with sensitive values excluded. For positional placeholders, count every question mark and compare it with the parameter array. For named placeholders, list the unique names and compare them with the bound keys.
A common bug is adding a WHERE clause conditionally but forgetting to add the corresponding parameter, or adding the parameter even when the condition was not added.
Be careful with IN clauses
One placeholder does not automatically expand to an array. `WHERE id IN (?)` with an array value is not equivalent to several placeholders. Generate the correct number of placeholders and merge the values into the final parameter list.
Wrap query-building logic in small functions and test combinations of optional filters so placeholder mismatches are caught before production.
Prefer one binding style
Avoid mixing named and positional placeholders in the same statement. Consistency makes dynamic SQL easier to reason about. If a query is complex enough that parameter management becomes fragile, a query builder can help — but understanding the final SQL remains essential.
Turn the idea into a clear implementation plan.
Use TWE to structure requirements first. If you later want implementation, Valron can pick up the same brief.