What is prepared statement
Prepares the SQL query, and returns a statement handle to be used for further operations on the statement. The query must consist of a single SQL statement.
The parameter markers must be bound to application variables using mysqli_stmt_bind_param() and/or mysqli_stmt_bind_result() before executing the statement or fetching rows.
The query, as a string.
You should not add a terminating semicolon or \g to the statement.
This parameter can include one or more parameter markers in the SQL statement by embedding question mark (? ) characters at the appropriate positions.
The markers are legal only in certain places in SQL statements. For example, they are allowed in the VALUES() list
of an INSERT statement (to specify column values for a row), or in a comparison with a column in a WHERE clause to specify a comparison value.
However, they are not allowed for identifiers (such as table or column names), in the select list that names the columns to be returned by a SELECT statement, or to specify both operands of a binary operator such as the = equal sign. The latter restriction is necessary because it would be impossible to determine the parameter type. It's not allowed to compare marker with NULL by ? IS NULL too. In general, parameters are legal only in Data Manipulation Language (DML) statements, and not in Data Definition Language (DDL) statements.Source: php.net