MySQL Reference Manual for version 3.23.15-alpha. - 22 How MySQL compares to other databases
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22 How MySQL compares to other databases
22.1 How MySQL compares to mSQL
This section has been written by the MySQL developers, so it
should be read with that in mind. But there are NO factual errors that
we know of.
For a list of all supported limits, functions and types, see the
crash-me web page.
Performance
For a true comparison of speed, consult the growing MySQL benchmark
suite. See section 11.7 Using your own benchmarks.
Because there is no thread creation overhead, a small parser, few features and
simple security, mSQL should be quicker at:
Tests that perform repeated connects and disconnects, running a very simple
query during each connection.
INSERT operations into very simple tables with few columns and keys.
CREATE TABLE and DROP TABLE.
SELECT on something that isn't an index. (A table scan is very
easy.)
Because these operations are so simple, it is hard to be better at them when
you have a higher startup overhead. After the connection is established,
MySQL should perform much better.
On the other hand, MySQL is much faster than mSQL (and
most other SQL implementions) on the following:
Complex SELECT operations.
Retrieving large results (MySQL has a better, faster and safer
protocol).
Tables with variable-length strings, because MySQL has more efficent
handling and can have indexes on VARCHAR columns.
Handling tables with many columns.
Handling tables with large record lengths.
SELECT with many expressions.
SELECT on large tables.
Handling many connections at the same time. MySQL is fully
multi-threaded. Each connection has its own thread, which means that
no thread 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 first has finished, regardless
of whether the connection is running a query that is short or long. When the
first 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 15000 times
slower than MySQL was seen. This is due to mSQL's lack of a
join optimizer 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 11.7 Using your own benchmarks.
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 supports a full GROUP BY with both HAVING and
the following functions: COUNT(), AVG(), MIN(),
MAX(), SUM() and STD(). COUNT(*) is optimized 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 can do calculations in an INSERT or UPDATE.
For example:
mysql> UPDATE SET x=x*10+y WHERE x<20;
Aliasing.
MySQL has column aliasing.
Qualifying column names.
In MySQL, if a column name is unique among the tables used in a
query, you do not have to use the full qualifier.
SELECT with functions.
MySQL has many functions (too many to list here; see section 7.4 Functions for use in SELECT and WHERE clauses).
Disk space efficiency
That is, how small can you make your tables?
MySQL 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 100,000,000 records,
saving even one byte per record is very important.
mSQL2 has a more limited set of column types, so it is
more difficult to get small tables.
Stability
This is harder to judge objectively. For a discussion of MySQL
stability, see section 1.6 How stable is MySQL?.
We have no experience with mSQL stability, so we cannot say
anything about that.
Price
Another important issue is the license. MySQL has a
more flexible license than mSQL, and is also less expensive than
mSQL. Whichever product you choose to use, remember to at least
consider paying for a license or email support. (You are required to get
a license if you include MySQL with a product that you sell,
of course.)
Perl interfaces
MySQL has basically the same interfaces to Perl as mSQL with
some added features.
JDBC (Java)
MySQL currently has 4 JDBC drivers:
The gwe driver: A Java interface by GWE technologies (not supported anymore).
The jms driver: An improved gwe driver by Xiaokun Kelvin ZHU
The twz driver: A type 4 JDBC driver by Terrence W. Zellers
and educational use.
The mm driver: A type 4 JDBC driver by Mark Matthews
The recommended drivers are the twz or mm driver. Both are reported to work
excellently.
We know that mSQL has a JDBC driver, but we have too little experience
with it to compare.
Rate of development
MySQL has a very small team of developers, but we are quite
used to coding C and C++ very rapidly. Because threads, functions,
GROUP BY and so on are still not implemented in mSQL, it
has a lot of catching up to do. To get some perspective on this, you
can view the mSQL `HISTORY' file for the last year and
compare it with the News section of the MySQL Reference Manual
(see section E MySQL change history). It should be pretty obvious which one has developed
most rapidly.
Utility programs
Both mSQL and MySQL have many interesting third-party
tools. Because it is very easy to port upward (from mSQL to
MySQL), almost all the interesting applications that are available for
mSQL are also available for MySQL.
MySQL comes with a simple msql2mysql program that fixes
differences in spelling between mSQL and MySQL for the
most-used C API functions.
For example, it changes instances of msqlConnect() to
mysql_connect(). Converting a client program from mSQL to
MySQL usually takes a couple of minutes.
22.1.1 How to convert mSQL tools for MySQL
According to our experience, it would just take a few hours to convert tools
such as msql-tcl and msqljava that use the
mSQL C API so that they work with the MySQL C API.
The conversion procedure is:
Run the shell script msql2mysql on the source. This requires the
replace program, which is distributed with MySQL.
Compile.
Fix all compiler errors.
Differences between the mSQL C API and the MySQL C API are:
MySQL uses a MYSQL structure as a connection type (mSQL
uses an int).
mysql_connect() takes a pointer to a MYSQL structure as a
parameter. It is easy to define one globally or to use malloc() to get
one.
mysql_connect() also takes 2 parameters for specifying the user and
password. You may set these to NULL, NULL for default use.
mysql_error() takes the MYSQL structure as a parameter. Just add
the parameter to your old msql_error() code if you are porting old code.
MySQL returns an error number and a text error message for all
errors. mSQL returns only a text error message.
Some incompatibilities exist as a result of MySQL supporting
multiple connections to the server from the same process.
22.1.2 How mSQL and MySQL client/server communications protocols differ
There are enough differences that it is impossible (or at least not easy)
to support both.
The most significant ways in which the MySQL protocol differs
from the mSQL protocol are listed below:
A message buffer may contain many result rows.
The message buffers are dynamically enlarged if the query or the
result is bigger than the current buffer, up to a configurable server and
client limit.
All packets are numbered to catch duplicated or missing packets.
All column values are sent in ASCII. The lengths of columns and rows are sent
in packed binary coding (1, 2 or 3 bytes).
MySQL can read in the result unbuffered (without having to store the
full set in the client).
If a single write/read takes more than 30 seconds, the server closes
the connection.
If a connection is idle for 8 hours, the server closes the connection.
22.1.3 How mSQL 2.0 SQL syntax differs from MySQL
Column types
MySQL
Has the following additional types (among others; see
see section 7.7 CREATE TABLE syntax):
ENUM type for one of a set of strings.
SET type for many of a set of strings.
BIGINT type for 64-bit integers.
MySQL also supports
the following additional type attributes:
UNSIGNED option for integer columns.
ZEROFILL option for integer columns.
AUTO_INCREMENT option for integer columns that are a
PRIMARY KEY.
See section 21.4.29 mysql_insert_id().
DEFAULT value for all columns.
mSQL2
mSQL column types correspond to the MySQL types shown below:
mSQL type Corresponding MySQL type
CHAR(len) CHAR(len)
TEXT(len) TEXT(len). len is the maximal length.
And LIKE works.
INT INT. With many more options!
REAL REAL. Or FLOAT. Both 4- and 8-byte versions are available.
UINT INT UNSIGNED
DATE DATE. Uses ANSI SQL format rather than mSQL's own.
TIME TIME
MONEY DECIMAL(12,2). A fixed-point value with two decimals.
Index creation
MySQL
Indexes may be specified at table creation time with the CREATE TABLE
statement.
mSQL
Indexes must be created after the table has been created, with separate
CREATE INDEX statements.
To insert a unique identifier into a table
MySQL
Use AUTO_INCREMENT as a column type
specifier.
See section 21.4.29 mysql_insert_id().
mSQL
Create a SEQUENCE on a table and select the _seq column.
To obtain a unique identifier for a row
MySQL
Add a PRIMARY KEY or UNIQUE key to the table and use this.
New in 3.23.11: If the PRIMARY or UNIQUE key consists of only one
column and this is of type integer, one can also refer to it as
_rowid.
mSQL
Use the _rowid column. Observe that _rowid may change over time
depending on many factors.
To get the time a column was last modified
MySQL
Add a TIMESTAMP column to the table. This column is automatically set
to the current date and time for INSERT or UPDATE statements if
you don't give the column a value or if you give it a NULL value.
mSQL
Use the _timestamp column.
NULL value comparisons
MySQL
MySQL follows
ANSI SQL and a comparison with NULL is always NULL.
mSQL
In mSQL, NULL = NULL is TRUE. You
must change =NULL to IS NULL and <>NULL to
IS NOT NULL when porting old code from mSQL to MySQL.
String comparisons
MySQL
Normally, string comparisons are performed in case-independent fashion with
the sort order determined by the current character set (ISO-8859-1 Latin1 by
default). If you don't like this, declare your columns with the
BINARY attribute, which causes comparisons to be done according to the
ASCII order used on the MySQL server host.
mSQL
All string comparisons are performed in case-sensitive fashion with
sorting in ASCII order.
Case-insensitive searching
MySQL
LIKE is a case-insensitive or case-sensitive operator, depending on
the columns involved. If possible, MySQL uses indexes if the
LIKE argument doesn't start with a wildcard character.
mSQL
Use CLIKE.
Handling of trailing spaces
MySQL
Strips all spaces at the end of CHAR and VARCHAR
columns. Use a TEXT column if this behavior is not desired.
mSQL
Retains trailing space.
WHERE clauses
MySQL
MySQL correctly prioritizes everything (AND is evaluated
before OR). To get mSQL behavior in MySQL, use
parentheses (as shown below).
mSQL
Evaluates everything from left to right. This means that some logical
calculations with more than three arguments cannot be expressed in any
way. It also means you must change some queries when you upgrade to
MySQL. You do this easily by adding parentheses. Suppose you
have the following mSQL query:
mysql> SELECT * FROM table WHERE a=1 AND b=2 OR a=3 AND b=4;
To make MySQL evaluate this the way that mSQL would,
you must add parentheses:
mysql> SELECT * FROM table WHERE (a=1 AND (b=2 OR (a=3 AND (b=4))));
Access control
MySQL
Has tables to store grant (permission) options per user, host and
database. See section 6.8 How the privilege system works.
mSQL
Has a file `mSQL.acl' in which you can grant read/write privileges for
users.
22.2 How MySQL compares to PostgreSQL
PostgreSQL has some more advanced features like user-defined
types, triggers, rules and some transaction support. However, PostgreSQL lacks
many of the standard types and functions from ANSI SQL and ODBC. See the
crash-me web page
for a complete list of limits and which types and functions are supported
or unsupported.
Normally, PostgreSQL is a magnitude slower than
MySQL. See section 11.7 Using your own benchmarks. This is due largely to their
transactions system. If you really need transactions or the rich type
system PostgreSQL offers and you can afford the speed penalty, you
should take a look at PostgreSQL.
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