【SQL篇章】【SQL语句梳理 :--基于MySQL5.6】【已梳理:CREATE TABLE】【会坚持完善】
SQL :
1. Data Definition Statements:
1.3 CREATE TABLE
格式:3种建表语句
1.简单SQL表明结构:
CREATE TABLE t7(id INT ,NAME VARCHAR(20), PRIMARY KEY(`id`)) ENGINE=INNODB;
格式:
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name (create_definition,...) [table_options] [partition_options]
2.简单SQL表名结构:
CREATE TABLE t7(id INT,TIME TIMESTAMP) AS SELECT id,TIME FROM t1 ;
【备注】:MySQL5.6.9之后,若开启GTID模式,参数enforce_gtid_consistency=on会限制此种SQL的执行而报错。
格式:
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name [(create_definition,...)] [table_options] [partition_options] [IGNORE | REPLACE] [AS] query_expression
3.简单SQL表明结构:
CREATE TABLE t7 like t1;
格式:
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name { LIKE old_tbl_name | (LIKE old_tbl_name) }
tb_name:
1.格式:
tb1_name 或者 `tb1_name`
db1.tb1_name 或者 `db1`.`tb1_name`
2.IF NOT EXISTS
不存在时,创建。避免表名重复出现错误。
data_type
1.AUTO_INCREMENT只用于:integer和floating point.不用于:BLOD和TEXT类型。
eg:CREATE TABLE t1 (c CHAR(20) CHARACTER SET utf8 COLLATE utf8_bin);
4.只有InnoDB和MyISAM 支持在BLOB和TEXT上设置索引
eg:
CREATE TABLE t2 (blob_col BLOB, INDEX(blob_col(10)));
NOT NULL | NULL
1.如果不指定NOT NULL和NULL,默认是NULL
2.在MySQL5.6中只有innodb,myisam,memory存储引擎,支持在列值有NULL的列上建索引。其它情况必须声 明所建索引列not null。
DEFAULT
1.设置列的默认值,必须使常量。不能设置为函数:NOW(),CURRENT_DATE()
2.当列为:DATETIME或TIMESTAMP时,可以设置default为:CURRENT_TIMESTAMP
3.如果没有default值,会根据列的类型,默认指定default值。/*其它文章会梳理着部分内容*/
4.BLOB和TEXT类型,不会指定默认值。
5.注意strict mode开启时的限制,例如:NO_ZERO_IN_DATE
例句:
CREATE TABLE `t2` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`num` int(11) NOT NULL DEFAULT '0',
`logintime` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
AUTO_INCREMENT
1.自增列,一表只能有一个,必须使用索引,不能有默认值。自增步长和起始可以通过参数设置,也可通过建表语句指定。
事例:
CREATE TABLE t2(
id INT NOT NULL AUTO_INCREMENT,
num INT NOT NULL DEFAULT 0,
logintime TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)
)ENGINE=INNODB AUTO_INCREMENT=100;
插入数据:
mysql> insert into t2(num) values(1);
Query OK, 1 row affected (0.12 sec) mysql> insert into t2(num) values(2);
Query OK, 1 row affected (0.01 sec)
mysql> select * from t2;
+-----+-----+---------------------+
| id | num | logintime |
+-----+-----+---------------------+
| 100 | 1 | 2016-11-16 14:45:20 |
| | 2 | 2016-11-16 14:45:25 |
+-----+-----+---------------------+
2 rows in set (0.00 sec)
通过两个参数分别设置:递增量和起始数值
mysql> show variables like '%auto_inc%';
+--------------------------+-------+
| Variable_name | Value |
+--------------------------+-------+
| auto_increment_increment | 1 |
| auto_increment_offset | 1 |
+--------------------------+-------+
COMMENT
字段描述:可以通过show create table;show full columns;查看显示:
事例:
CREATE TABLE t4(
id INT NOT NULL AUTO_INCREMENT COMMENT '序列号',
num INT NOT NULL DEFAULT 0 COMMENT '电话号码',
logintime TIMESTAMP DEFAULT CURRENT_TIMESTAMP COMMENT '登录时间',
PRIMARY KEY (`id`)
)ENGINE=INNODB AUTO_INCREMENT=100 ;
查看:
mysql> show full columns from t4;
+-----------+-----------+-----------+------+-----+-------------------+----------------+---------------------------------+--------------+
| Field | Type | Collation | Null | Key | Default | Extra | Privileges | Comment |
+-----------+-----------+-----------+------+-----+-------------------+----------------+---------------------------------+--------------+
| id | int(11) | NULL | NO | PRI | NULL | auto_increment | select,insert,update,references | 序列号 |
| num | int(11) | NULL | NO | | 0 | | select,insert,update,references | 电话号码 |
| logintime | timestamp | NULL | NO | | CURRENT_TIMESTAMP | | select,insert,update,references | 登录时间 |
+-----------+-----------+-----------+------+-----+-------------------+----------------+---------------------------------+--------------+
3 rows in set (0.00 sec)
COLUMN_FORMAT
- 一般用于NDB表的个别列。
- FIXED:指定固定的列宽度
- DYNAMIC:指定可变列宽度
- DEFAULT:两者都可用,根据列类型自动选择。
- 对于NDB表,COLUMN_FORMAT是:DEFAULT.对于非NDB引擎表是没有效果的,MySQL5.6之后,默认不开启。STORAGE
事例:
只适用于:NDB引擎
CREATE TABLE t5 (
c1 INT STORAGE DISK,
c2 INT STORAGE MEMORY
) ENGINE NDB; CREATE TABLE t1 (
c1 INT STORAGE DISK,
c2 INT STORAGE MEMORY
) TABLESPACE ts_1 ENGINE NDB;
CREATE TABLE ... LIKE
格式:
CREATE TABLE new_tbl LIKE orig_tbl;
基于另一个表创建空表,包括表的列和索引的定义。
事例:
create table t4 like t2;
t2表的定义:
mysql> desc t2;
+-----------+-----------+------+-----+-------------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+-----------+------+-----+-------------------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| num | int(11) | NO | | 0 | |
| logintime | timestamp | NO | | CURRENT_TIMESTAMP | |
+-----------+-----------+------+-----+-------------------+----------------+
t4表的定义:
mysql> desc t4;
+-----------+-----------+------+-----+-------------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+-----------+------+-----+-------------------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| num | int(11) | NO | | 0 | |
| logintime | timestamp | NO | | CURRENT_TIMESTAMP | |
+-----------+-----------+------+-----+-------------------+----------------+
注意:
1.从MySQL5.6.1开始,当另一个表处于:LOCK TABLE状态时,不能create table. . . like
2.当创建新表时的sql_mode和创建原表的sql_mode不同时,表的定义对于新的sql_mode是无效的,导致创建语句失败。
CREATE TABLE ... SELECT
格式:
CREATE TABLE new_tbl [AS] SELECT * FROM orig_tbl;
1.只会复制表结构,不复制索引;可以复制指定列。
2.创建表的列和 select后面的列,要保持一致。
事例:
原表s1:
mysql> desc s1;
+---------+-------------+------+-----+-------------------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+-------------------+-------+
| id | int(11) | NO | PRI | NULL | |
| name | varchar(20) | YES | | NULL | |
| LogTime | timestamp | YES | | CURRENT_TIMESTAMP | |
+---------+-------------+------+-----+-------------------+-------+
mysql> select * from s1;
+----+------+---------------------+
| id | name | LogTime |
+----+------+---------------------+
| 1 | kata | 2016-11-16 16:01:48 |
+----+------+---------------------+
创建新表s2、s3
create table s2 as select * from s1;
mysql> desc s2;
+---------+-------------+------+-----+-------------------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+-------------------+-------+
| id | int(11) | NO | | NULL | |
| name | varchar(20) | YES | | NULL | |
| LogTime | timestamp | YES | | CURRENT_TIMESTAMP | |
+---------+-------------+------+-----+-------------------+-------+
mysql> select * FROM s2;
+----+------+---------------------+
| id | name | LogTime |
+----+------+---------------------+
| 1 | kata | 2016-11-16 16:01:48 |
+----+------+---------------------+
创建表s3
create table s3 as select id,name from s2;
mysql> desc s3;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | NO | | NULL | |
| name | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
mysql> select * from s3;
+----+------+
| id | name |
+----+------+
| 1 | kata |
+----+------+
创建表时指定新的列名:前后列一致
create table s4(Sid int,Sname varchar(10)) as select id as 'Sid',name as 'Sname' from s1;
mysql> desc s4;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| Sid | int(11) | YES | | NULL | |
| Sname | varchar(10) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
创建表时指定的列名:前后不一致时:结果异常
mysql> create table s7(Sid int,Sname varchar(10)) as select id,name from s1;
异常结果:
mysql> desc s7;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| Sid | int(11) | YES | | NULL | |
| Sname | varchar(10) | YES | | NULL | |
| id | int(11) | NO | | NULL | |
| name | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
表的物理文件
1.表文件的存储由配置参数:innodb_file_per_table决定
MySQL版本:<= 5.6.5 默认OFF
MySQL版本:>= 5.6.6 默认ON
参数配置开启ON:innodb会将表的data和indexs存储在单独的文件里:.ibd
参数配置关闭OFF: innodb会将表的data和indexs存储在:系统表空间文件:一个或多个 ibdata* files.
2.MYISAM表的数据文件结构
File | Purpose |
tbl_name.frm | Table format (definition) file |
tbl_name.MYD | Data file |
tbl_name.MYI | Index file |
备注:关于临时表 字段类型和表索引 部分单独梳理!!!