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Table of Contents
1. General Information
2. MySQL Installation
3. Tutorial Introduction
4. Database Administration
5. MySQL Optimisation
6. MySQL Language Reference
7. MySQL Table Types
8. MySQL APIs
9. Extending MySQL

562 MySQL Technical Reference for Version 4.0.3 even if you determine in mid-retrieval that you've found the information you were looking for. The API makes it possible for clients to respond appropriately to queries (retrieving rows only as necessary) without knowing whether or not the query is a SELECT. You can do this by calling mysql_store_result() after each mysql_query() (or mysql_real_query()). If the result set call succeeds, the query was a SELECT and you can read the rows. If the result set call fails, call mysql_field_count() to determine whether a result was actually to be expected. If mysql_field_count() returns zero, the query returned no data (indicating that it was an INSERT, UPDATE, DELETE, etc.), and was not expected to return rows. If mysql_field_count() is non-zero, the query should have returned rows, but didn't. This indicates that the query was a SELECT that failed. See the description for mysql_field_ count() for an example of how this can be done. Both mysql_store_result() and mysql_use_result() allow you to obtain information about the elds that make up the result set (the number of elds, their names and types, etc.). You can access eld information sequentially within the row by calling mysql_fetch_ field() repeatedly, or by eld number within the row by calling mysql_fetch_field_ direct(). The current eld cursor position may be changed by calling mysql_field_ seek(). Setting the eld cursor aects subsequent calls to mysql_fetch_field(). You can also get information for elds all at once by calling mysql_fetch_fields(). For detecting and reporting errors, MySQL provides access to error information by means of the mysql_errno() and mysql_error() functions. These return the error code or error message for the most recently invoked function that can succeed or fail, allowing you to determine when an error occurred and what it was. 8.4.3 C API Function Descriptions In the descriptions here, a parameter or return value of NULL means NULL in the sense of the C programming language, not a MySQL NULL value. Functions that return a value generally return a pointer or an integer. Unless specied otherwise, functions returning a pointer return a non-NULL value to indicate success or a NULL value to indicate an error, and functions returning an integer return zero to indicate success or non-zero to indicate an error. Note that \non-zero" means just that. Unless the function description says otherwise, do not test against a value other than zero: if (result) /* correct */ ... error ... if (result < 0) /* incorrect */ ... error ... if (result == -1) /* incorrect */ ... error ... When a function returns an error, the Errors subsection of the function description lists the possible types of errors. You can nd out which of these occurred by calling mysql_errno(). A string representation of the error may be obtained by calling mysql_error().

MySQL Reference Manual

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