OOPHP_02.book Page 148 Friday, May 5, 2006 2:25 PM
you will get something more meaningful. Forcing a warning by referencing a nonexistent table results in the following, more specific, output: Warning: SQLiteDatabase::query()[function.query]: no such table: tblnonexistent...
Query Methods Look again at Listing 15-4. It includes the five methods for creating result sets. The buffered and unbuffered methods are fairly self-explanatory—you are probably quite familiar with the equivalent MySQL functions. However, MySQL (prior to the MySQL improved extension) has nothing to match the singleQuery, queryExec, or arrayQuery methods. Let’s look at these methods in more detail. The singleQuery method is a recent addition, and the PHP site warns that it is not currently documented. Let’s carry on regardless because this method looks especially useful for those situations where a query returns only one row—when using the COUNT function to return the number of records in a table, for example. Here’s one view of how this method ought to behave: This method returns only one record, and no result set is created. If the second argument is false, the value returned is an array of the first row. If the second argument is true, then only the first column of the first row is returned, and it is returned as a scalar value. This speculation may make the best sense of how this method ought to work, but it doesn’t describe what actually happens. In fact, this method only ever returns the first column and any number of rows. If the second argument is false, then an array is returned; if the second argument is true and only one row is returned, a scalar is returned. On the PHP site, this second argument is identified as bool first_row_only and the return type is identified as an array. It looks like the return type should be mixed. In any case, this method doesn’t yet work the way it ought to. We were warned. There is no requirement that you use the singleQuery method instead of query. As with MySQL, you can always create a result set and then use the appropriate fetch function to retrieve the value of the first row or a specific field. But why return an object or an array when all that’s needed is the value of one column? You may use the singleQuery method for any kind of query— data manipulation or otherwise—but it was designed specifically for situations where a single value or single column is returned, and is presumably optimized for this situation. As you can see, there is also an arrayQuery method. Like the singleQuery method, this method allows us to directly copy results into an array, bypassing the intermediate step of creating a result set. This method is best used when a limited number of records are returned. MySQL versions prior to 4.1 have no equivalent to the queryExec method of SQLite because queryExec is specifically designed for use with multiple queries. Multiple, semicolon-separated queries may be passed as a single query string to queryExec. (The install script uses this method to create the tables, triggers, and views and to insert records into the tblresources table.) This method gives significant performance improvements over repeated querying and performs 148
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