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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
    Chapter 1:  General Information 51 has to wait for another (unless a thread is modifying a table another thread wants to access).  In  mSQL,  once one connection is established,  all others must wait until the rst has nished, regardless of whether the connection is running a query that is short or long. When the rst connection terminates, the next can be served, while all the others wait again, etc.    Joins.    mSQL  can  become  pathologically  slow  if  you  change  the  order  of tables in a SELECT.  In the benchmark suite, a time more than 15,000 times slower than MySQL Server was seen.  This is due to mSQL's lack of a join optimiser  to  order  tables  in  the  optimal  order.   However,  if  you  put  the tables in exactly the right order in mSQL2 and the WHERE is simple and uses index columns, the join will be relatively fast!  See Section 5.1.4 [MySQL Benchmarks], page 336.    ORDER BY and GROUP BY.    DISTINCT.    Using TEXT or BLOB columns. SQL Features    GROUP BY  and  HAVING.   mSQL  does  not  support  GROUP BY  at  all.   MySQL Server supports a full GROUP BY with both HAVING and the following func- tions:   COUNT(),  AVG(),  MIN(),  MAX(),  SUM(),  and  STD().   COUNT(*)  is optimised  to  return  very  quickly  if  the  SELECT  retrieves  from  one  table, no other columns are retrieved, and there is no WHERE clause.  MIN() and MAX() may take string arguments.    INSERT  and  UPDATE  with calculations.  MySQL Server can do calculations in an INSERT or UPDATE.  For example: mysql> UPDATE SET x=x*10+y WHERE x<20;    Aliasing.  MySQL Server has column aliasing.    Qualifying column names.  In MySQL Server, if a column name is unique among the tables used in a query, you do not have to use the full quali er.    SELECT  with functions.  MySQL Server has many functions (too many to list here; see Section 6.3 [Functions], page 406). Disk Space Eciency That is, how small can you make your tables? MySQL Server has very precise types, so you can create tables that take very little space.  An example of a useful MySQL datatype is the MEDIUMINT that is 3 bytes long.  If you have 100 million records, saving even 1 byte per record is very important. mSQL2 has a more limited set of column types, so it is more dicult to get small tables. Stability This is harder to judge objectively.  For a discussion of MySQL Server stability, see Section 1.2.3 [Stability], page 7. We have no experience with  mSQL  stability, so we cannot say anything about that.
     

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