(mysql.info.gz) No matching rows

Info Catalog

(mysql.info.gz) Deleting from related tables

(mysql.info.gz) Query Issues

(mysql.info.gz) Problems with float

 
 A.5.7 Solving Problems with No Matching Rows
 --------------------------------------------
 
 If you have a complicated query that uses many tables but that doesn't
 return any rows, you should use the following procedure to find out what
 is wrong:
 
   1. Test the query with `EXPLAIN' to check whether you can find
      something that is obviously wrong.   `EXPLAIN' EXPLAIN.
 
   2. Select only those columns that are used in the `WHERE' clause.
 
   3. Remove one table at a time from the query until it returns some
      rows.  If the tables are large, it's a good idea to use `LIMIT 10'
      with the query.
 
   4. Issue a `SELECT' for the column that should have matched a row
      against the table that was last removed from the query.
 
   5. If you are comparing `FLOAT' or `DOUBLE' columns with numbers that
      have decimals, you can't use equality (`=') comparisons. This
      problem is common in most computer languages because not all
      floating-point values can be stored with exact precision.  In some
      cases, changing the `FLOAT' to a `DOUBLE' will fix this.  
      Problems with float.
 
   6. If you still can't figure out what's wrong, create a minimal test
      that can be run with `mysql test < query.sql' that shows your
      problems.  You can create a test file by dumping the tables with
      `mysqldump --quick db_name TBL_NAME_1 ... TBL_NAME_N > query.sql'.
      Open the file in an editor, remove some insert lines (if there are
      more than needed to demonstrate the problem), and add your
      `SELECT' statement at the end of the file.
 
      Verify that the test file demonstrates the problem by executing
      these commands:
 
           shell> mysqladmin create test2
           shell> mysql test2 < query.sql
 
      Post the test file using `mysqlbug' to the general MySQL mailing
      list.   Mailing-list.
 

Info Catalog

(mysql.info.gz) Deleting from related tables

(mysql.info.gz) Query Issues

(mysql.info.gz) Problems with float