一、数据库内容
1、创建数据库
如果重复创建会提示存在，添加 IF NOT EXISTS 则不存在问题
location默认的是在hdfs上use/werehost上面，如果自己指定的是不带DB的，需要创建

官网语法：

CREATE (DATABASE|SCHEMA) [IF NOT EXISTS] database_name
[COMMENT database_comment]
[LOCATION hdfs_path]
[WITH DBPROPERTIES (property_name=property_value, ...)];

示例：
hive (default)> create database d7_hive;
OK
Time taken: 12.868 seconds
hive (default)> show databases;
OK
database_name
d7_hive
default
Time taken: 0.576 seconds, Fetched: 2 row(s)
如果重复创建会提示存在，添加 IF NOT EXISTS 则不存在问题
hive (default)> reate database d7_hive;
FAILED: Execution Error, return code 1 from org.apache.hadoop.hive.ql.exec.DDLTask. Database ruozedata already exists

hive (default)> create database if not exists d7_hive;
OK
Time taken: 0.017 seconds
不指定创建数据库路径，默认创建在/user/hive/warehouse目录下，有一个数据库名.db的文件夹
[hadoop@hadoop001 ~]$ hdfs dfs -ls /user/hive/warehouse
Found 2 items
drwxr-xr-x   - hadoop supergroup          0 2019-07-28 00:02 /user/hive/warehouse/d7_hive.db
drwxr-xr-x   - hadoop supergroup          0 2019-07-27 18:02 /user/hive/warehouse/hello
指定创建数据库目录，自己指定的是不带DB的，需要创建，创建好之后对应的文件夹下面会有对应的文件
需要注意的创建表默认是内部表，指定EXTERNAL则是外部表，两者的区别在于删除时内部表hdfs上数据和元数据都会被删除，外部表只删除元数据不会。
hive (default)> use d7_hive;
OK
Time taken: 0.153 seconds
hive (d7_hive)> create table hello(id int,name string)
              > row format delimited fields terminated by ',';
OK
Time taken: 2.172 seconds
hive (d7_hive)> 
              > load data local inpath '/home/hadoop/data/hello.txt' overwrite into table hello;
Loading data to table d7_hive.hello
Table d7_hive.hello stats: [numFiles=1, totalSize=28]
OK
Time taken: 3.102 seconds

2、删除数据库
数据库删除的时候，只要库下有表，默认就不能删除
如果必须删除，在语句后加入cascade
CASCADE慎用

官网语法：

DROP (DATABASE|SCHEMA) [IF EXISTS] database_name [RESTRICT|CASCADE];

删除的时候提示错误，库下存在一个或多个表
hive (default)> DROP DATABASE IF EXISTS d7_hive;
FAILED: Execution Error, return code 1 from org.apache.hadoop.hive.ql.exec.DDLTask. InvalidOperationException(message:Database d7_hive is not empty. One or more tables exist.)
语句后加入cascade可删除，但要慎用

3、元数据的信息关联
mysql>show tables;——几个重要的表：

VERSION表中有且只能存在一条记录，描述表的信息
DBS databases 库
TBLS tables 表
COLUMNS_V2 描述表的字段

mysql>select * from DBS;
mysql>select * from DBS \G;
每一个SQL语句底层都有相应的元数据信息做关联
数据库创建完成后，元数据信息在DBS表里面

二、表的内容

字段的数据类型
*****数值：int、bigint、float、double
*****字符串：string 至少90%会用到
时间类型可以使用字符串类型： string
BOOLEAN：true false 用0/1会更简单

分隔符
字段和字段分隔符、行与行的分隔符
字段和字段分隔符：hive里面默认的分隔符 \001 ^A ，生产上最多的是， 逗号、空格、制表符tab
行与行的分隔符 ：\n

举例：
1,ruoze
2,jepson
3,xingxing
==> row format delimited fields terminated by ‘,’;

1、创建表

官方语法
CREATE [TEMPORARY] [EXTERNAL] TABLE [IF NOT EXISTS] [db_name.]table_name    -- (Note: TEMPORARY available in Hive 0.14.0 and later)
  [(col_name data_type [COMMENT col_comment], ... [constraint_specification])]
  [COMMENT table_comment]
  [PARTITIONED BY (col_name data_type [COMMENT col_comment], ...)]
  [CLUSTERED BY (col_name, col_name, ...) [SORTED BY (col_name [ASC|DESC], ...)] INTO num_buckets BUCKETS]
  [SKEWED BY (col_name, col_name, ...)                  -- (Note: Available in Hive 0.10.0 and later)]
     ON ((col_value, col_value, ...), (col_value, col_value, ...), ...)
     [STORED AS DIRECTORIES]
  [
   [ROW FORMAT row_format] 
   [STORED AS file_format]
     | STORED BY 'storage.handler.class.name' [WITH SERDEPROPERTIES (...)]  -- (Note: Available in Hive 0.6.0 and later)
  ]
  [LOCATION hdfs_path]
  [TBLPROPERTIES (property_name=property_value, ...)]   -- (Note: Available in Hive 0.6.0 and later)
  [AS select_statement];   -- (Note: Available in Hive 0.5.0 and later; not supported for external tables)
 
CREATE [TEMPORARY] [EXTERNAL] TABLE [IF NOT EXISTS] [db_name.]table_name
  LIKE existing_table_or_view_name
  [LOCATION hdfs_path];
 
data_type
  : primitive_type
  | array_type
  | map_type
  | struct_type
  | union_type  -- (Note: Available in Hive 0.7.0 and later)
 
primitive_type
  : TINYINT
  | SMALLINT
  | INT
  | BIGINT
  | BOOLEAN
  | FLOAT
  | DOUBLE
  | DOUBLE PRECISION -- (Note: Available in Hive 2.2.0 and later)
  | STRING
  | BINARY      -- (Note: Available in Hive 0.8.0 and later)
  | TIMESTAMP   -- (Note: Available in Hive 0.8.0 and later)
  | DECIMAL     -- (Note: Available in Hive 0.11.0 and later)
  | DECIMAL(precision, scale)  -- (Note: Available in Hive 0.13.0 and later)
  | DATE        -- (Note: Available in Hive 0.12.0 and later)
  | VARCHAR     -- (Note: Available in Hive 0.12.0 and later)
  | CHAR        -- (Note: Available in Hive 0.13.0 and later)
 
array_type
  : ARRAY < data_type >
 
map_type
  : MAP < primitive_type, data_type >
 
struct_type
  : STRUCT < col_name : data_type [COMMENT col_comment], ...>
 
union_type
   : UNIONTYPE < data_type, data_type, ... >  -- (Note: Available in Hive 0.7.0 and later)
 
row_format
  : DELIMITED [FIELDS TERMINATED BY char [ESCAPED BY char]] [COLLECTION ITEMS TERMINATED BY char]
        [MAP KEYS TERMINATED BY char] [LINES TERMINATED BY char]
        [NULL DEFINED AS char]   -- (Note: Available in Hive 0.13 and later)
  | SERDE serde_name [WITH SERDEPROPERTIES (property_name=property_value, property_name=property_value, ...)]
 
file_format:
  : SEQUENCEFILE
  | TEXTFILE    -- (Default, depending on hive.default.fileformat configuration)
  | RCFILE      -- (Note: Available in Hive 0.6.0 and later)
  | ORC         -- (Note: Available in Hive 0.11.0 and later)
  | PARQUET     -- (Note: Available in Hive 0.13.0 and later)
  | AVRO        -- (Note: Available in Hive 0.14.0 and later)
  | JSONFILE    -- (Note: Available in Hive 4.0.0 and later)
  | INPUTFORMAT input_format_classname OUTPUTFORMAT output_format_classname
 
constraint_specification:
  : [, PRIMARY KEY (col_name, ...) DISABLE NOVALIDATE ]
    [, CONSTRAINT constraint_name FOREIGN KEY (col_name, ...) REFERENCES table_name(col_name, ...) DISABLE NOVALIDATE 

创建表
hive (default)> create table emp(
              > empno int, 
              > ename string, 
              > job string, 
              > mgr int, 
              > hiredate string, 
              > sal double, 
              > comm double, 
              > deptno int)
              > row format delimited fields terminated by ',';
OK
Time taken: 0.083 seconds

Create Table As Select (CTAS)
--------------------- 
重新拷贝一个表
CREATE [TEMPORARY] [EXTERNAL] TABLE [IF NOT EXISTS] [db_name.]table_name
LIKE existing_table_or_view_name
[LOCATION hdfs_path];

拷贝表结构，不拷贝表数据
CREATE TABLE ruozedata_emp2 LIKE ruozedata_emp;

如果不知道表结构，通过show create table ruozedata_emp;查看

真正拷贝一份数据
Create Table As Select (CTAS)
create table ruozedata_emp3 as select empno,ename,deptno from ruozedata_emp;

修改表名
ALTER TABLE 老表 RENAME TO 新表;
ALTER TABLE ruozedata_emp3 rename to ruozedata_emp3_bak;

删除表
DROP TABLE [IF EXISTS] table_name [PURGE]; 
DROP TABLE  table_name ruozedata_emp3_bak;
Truncate Table  删表的数据