For those of you still running a 7.3 instance with plans to migrate to 7.5 this FYI may be of interest.
There exists a bug in 7.3[.0.34] that for varchar(n) indexed fields a redefinition of the field length does not get pushed out to its index. When you migrate your instance to 7.5, the index with the old length is carried over but now the 7.5 version notices the mismatch and complains with the -3007 error. This occurs for queries that use a index-only optimizer strategy. The workaround is to drop and recreate the indexes that give you a headache. A permanent fix will be released in an upcoming version. Many thanks go to Becker and Elke for solving this issue. email subject association (added for search returns): 7.3 to 7.5 [NON-PARALLEL] Migration Explained (HOWTO)
