mysql 学习---->表优化、合成索引、浮点数与定点数

1.表优化  

mysql> use test1;  

Reading table information for completion of table and column names  

You can turn off this feature to get a quicker startup with -A  

Database changed  

  

mysql> alter table t rename t_old;
 

  

mysql> create table t ( id varchar(100),content text);
 

  

mysql> insert into t values  

    -> (1,repeat('haha',100)),  

    -> (2,repeat('test',100)),  

    -> (3,repeat('java',100));
 

  

mysql> insert into t select * from t;
 

  

mysql> alter table t rename t_optimize;  

mysql> select table_name,data_length from information_schema.tables where table_name = "t_optimize";  

+------------+-------------+  

| table_name | data_length |  

+------------+-------------+  

| t_optimize |       16384 |  

+------------+-------------+  

  

mysql> optimize table t_optimize;  

  

+------------------+----------+----------+-------------------------------------------------------------------+  

| Table            | Op       | Msg_type | Msg_text                                                          |  

+------------------+----------+----------+-------------------------------------------------------------------+  

| test1.t_optimize | optimize | note     | Table does not support optimize, doing recreate + analyze instead |  

| test1.t_optimize | optimize | status   | OK                                                                |  

+------------------+----------+----------+-------------------------------------------------------------------+  

  

mysql> select table_name,data_length from information_schema.tables where table_name = "t_optimize";  

+------------+-------------+  

| table_name | data_length |  

+------------+-------------+  

| t_optimize |       16384 |  

+------------+-------------+  

 

2.合成索引  

mysql> create table t (id varchar(100),context blob,hash_value varchar(40));
 

  

mysql> insert into t values(1,repeat('zhejiang',2),md5(context));
 

  

mysql> insert into t values(1,repeat('jiangsu',2),md5(context));
 

  

mysql> insert into t values(1,repeat('fujian 2008',2),md5(context));
 

  

mysql> select * from t;  

+------+------------------------+----------------------------------+  

| id   | context                | hash_value                       |  

+------+------------------------+----------------------------------+  

| 1    | zhejiangzhejiang       | 8f36854efa45585f35e6ca54b7d58f31 |  

| 1    | jiangsujiangsu         | e2817db97256ac13805ee1ccfc1048e7 |  

| 1    | fujian 2008fujian 2008 | 1efb8d993ee2cae7532407ff30b5778c |  

+------+------------------------+----------------------------------+  

  

mysql> select * from t ;  

+------+------------------------+----------------------------------+  

| id   | context                | hash_value                       |  

+------+------------------------+----------------------------------+  

| 1    | zhejiangzhejiang       | 8f36854efa45585f35e6ca54b7d58f31 |  

| 1    | jiangsujiangsu         | e2817db97256ac13805ee1ccfc1048e7 |  

| 1    | fujian 2008fujian 2008 | 1efb8d993ee2cae7532407ff30b5778c |  

+------+------------------------+----------------------------------+  

  

mysql> select * from t  

    ->  where hash_value=md5(repeat('fujian 2008',2));  

+------+------------------------+----------------------------------+  

| id   | context                | hash_value                       |  

+------+------------------------+----------------------------------+  

| 1    | fujian 2008fujian 2008 | 1efb8d993ee2cae7532407ff30b5778c |  

+------+------------------------+----------------------------------+  

  

mysql> desc t;  

+------------+--------------+------+-----+---------+-------+  

| Field      | Type         | Null | Key | Default | Extra |  

+------------+--------------+------+-----+---------+-------+  

| id         | varchar(100) | YES  |     | NULL    |       |  

| context    | blob         | YES  |     | NULL    |       |  

| hash_value | varchar(40)  | YES  |     | NULL    |       |  

+------------+--------------+------+-----+---------+-------+  

  

mysql>  create index inx_blob on t(context(100));
  

  

mysql> select * from t;  

+------+------------------------+----------------------------------+  

| id   | context                | hash_value                       |  

+------+------------------------+----------------------------------+  

| 1    | zhejiangzhejiang       | 8f36854efa45585f35e6ca54b7d58f31 |  

| 1    | jiangsujiangsu         | e2817db97256ac13805ee1ccfc1048e7 |  

| 1    | fujian 2008fujian 2008 | 1efb8d993ee2cae7532407ff30b5778c |  

+------+------------------------+----------------------------------+  

  

mysql> desc select * from t where context like 'fujian%' \G;  

*************************** 1. row ***************************  

           id: 1  

  select_type: SIMPLE  

        table: t  

         type: range  

possible_keys: inx_blob  

          key: inx_blob  

      key_len: 103  

          ref: NULL  

         rows: 1  

        Extra: Using where   

  

ERROR:   

No query specified  

  

mysql> desc select * from t where context like '%fujian' \G;  

*************************** 1. row ***************************  

           id: 1  

  select_type: SIMPLE  

        table: t  

         type: ALL  

possible_keys: NULL  

          key: NULL  

      key_len: NULL  

          ref: NULL  

         rows: 3  

        Extra: Using where  

1 row in set (0.00 sec)  

  

ERROR:   

No query specified
 

  

3.浮点数、定点数  

mysql> create table t(f float(8,1));
  

  

mysql> desc t;  

+-------+------------+------+-----+---------+-------+  

| Field | Type       | Null | Key | Default | Extra |  

+-------+------------+------+-----+---------+-------+  

| f     | float(8,1) | YES  |     | NULL    |       |  

+-------+------------+------+-----+---------+-------+  

  

mysql> insert into t values(1.23456);
 

  

mysql> select * from t;  

+------+  

| f    |  

+------+  

|  1.2 |  

+------+  

  

mysql> insert into t values(1.25456);
 

  

mysql> select * from t;  

+------+  

| f    |  

+------+  

|  1.2 |  

|  1.3 |  

+------+ 

  

mysql> create table test(c1 float(10,2),c2 decimal(10,2));
 

  

mysql> insert into test values(131072.32,131072.32);
 

  

mysql> select * from test;  

+-----------+-----------+  

| c1        | c2        |  

+-----------+-----------+  

| 131072.31 | 131072.32 |  

+-----------+-----------+