(mysql.info) no-matching-rows

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(mysql.info) deleting-from-related-tables

(mysql.info) query-issues

(mysql.info) 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. See  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' fixes this. See 
      problems-with-float.
 
      Similar problems may be encountered when comparing `DECIMAL'
      values prior to MySQL 5.0.3.
 
   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
 
      Attach the test file to a bug report, which you can file using the
      instructions in  bug-reports.
 

Info Catalog

(mysql.info) deleting-from-related-tables

(mysql.info) query-issues

(mysql.info) problems-with-float