表操作语句---DDL（建表、修改表等语句）
-
创建表
create [external] table [if not exists] table_name {external：外部表}
[(col_name data_type [comment col_comment],...)] {comment：说明} {每列}
[comment table_comment]
[partitioned by (col_name data_type [comment col_comment],...)] {分区表：分区的字段和类型}
[clustered by (col_name,col_name,...) [sorted by (col_name [asc|desc],...)] into num_buckets buckets]
{桶表：指定几个桶，按照哪个字段进行hash分桶，按照哪个字段排序}
[row format row_format]
{一行的格式：例如/n是一行，或者使用内置的格式，delimited默认的行分隔符，
fields terminated by ‘,’ 字段分隔符逗号，}
[stored as file_format] {文件格式，默认textfile}
[location hdfs_path] {创建外部表时用，指明当前外部表的路径}
data_type的集合类型：array、map、struct
例子：
1. create table student (id int, name string, age int)
row format delimited fields terminated by ',';
执行后生成一个student文件夹（ /user/hive/warehouse/db1.db/表名(例如student)/文件 ），添加数据后可生成文件例子：
1,张三,24
2,李四,25
3,王五,22
2. create table student (id int, name string, age int)
partitioned by (country string)
row format delimited fields terminated by ',';
执行后在表名文件夹后面生成分区文件夹（ /user/hive/warehouse/db1.db/表名(例如student)/分区名(例如country=china)/文件 ）
3. create table student (id int, name string, age int)
partitioned by (country string)
clustered by (id) sorted by (age) into 2 buckets
row format delimited fields terminated by ',';
桶的分配：id除以2取余，余数为0放到一个桶，余数为1放到另一个桶
4. create table b like a; {创建一个表b，和a表的字段一致，无数据}
- 修改表：alter table table_name
1. 增加分区：
alter table table_name add [if not exists] partition_spec [ location 'location1' ] partition_spec [ location 'location2' ] ;
partition_spec：partition (partition_col = partition_col_value, partition_col = partiton_col_value, ...)
例子：alter table student add partition(country='China') partition(country='UK');
alter table student add partition(country='China') location '/user/hive/warehouse/student' partition(country='UK');
2. 删除分区：
alter table table_name drop partition_spec, partition_spec,...;
例子：alter table student drop partition(country='China'), partition(country='UK');
3. 重命名表：
alter table table_name rename to new_table_name;
4. 增加列：
alter table table_name add columns (col_name data_type [comment col_comment],...) {增加列}
alter table table_name replace columns (col_name data_type [comment col_comment],...) {替换表中所有列}
alter table table_name change [column] col_old_name col_new_name column_type [comment col_comment] [first | after column_name] {修改字段和类型}
例子：alter table student add columns (city string); 增加列city
alter table student change column city school string; 修改字段city为school
- 其它一些命令：
show databases; use db1; show tables;
show partitions table_name; show functions;
create database db2; drop table table_name;
truncate table table_name; 清理表
desc table_name; 表字段描述
desc extended table_name; 附带表的详细信息
desc formatted table_name; 将表的详细信息格式为表格形式
!ls; 前面加‘!’，可以和linux本机交互
dfs -ls /; 前面加‘dfs -’，可以和hdfs交互