主要改进内容：
- The SQL output resulting from sqlite3_trace() is now modified to include the values of bound parameters.
- Performance optimizations targetting a specific use case from a
single high-profile user of SQLite. A 12% reduction in the number of
CPU operations is achieved (as measured by valgrind). Actual
performance improvements in practice may vary depending on workload.
Changes include:
- The ifnull() and coalesce()
SQL functions are now implemented using in-line VDBE code rather than
calling external functions, so that unused arguments need never be
evaluated.
- The substr() SQL function does not bother to measure the length its entire input string if it is only computing a prefix
- Unnecessary OP_IsNull, OP_Affinity, and OP_MustBeInt VDBE opcodes are suppressed
- Various code refactorizations for performance
- The FTS3 extension has undergone a major rework and cleanup. New FTS3 documentation is now available.
- The SQLITE_SECURE_DELETE compile-time option fixed to make sure that content is deleted even when the truncate optimization applies.
- Improvements to "dot-command" handling in the Command Line Interface.
- Other minor bug fixes and documentation enhancements.
下载地址：http://www.sqlite.org/sqlite-amalgamation-3_6_21.zip
