Question

我有一列insert_process_id，我想将其重命名为process_id。该外部表为实木复合地板文件格式。请告知如何重命名此列。

Answer 1

您可以使用以下语法

ALTER TABLE table_name [PARTITION partition_spec] CHANGE [COLUMN] col_old_name col_new_name column_type
  [COMMENT col_comment] [FIRST|AFTER column_name] [CASCADE|RESTRICT];

由于这是一个外部表，因此您可以删除该表并通过特定的更改重新创建。

Answer 2

您可以如下更改列名。

语法：

ALTER TABLE name CHANGE column_name col_spec ..

示例：

我创建了如下表。

CREATE EXTERNAL Table IF NOT EXISTS Patient_external(
PatientID int, Name String, City String, Number String )
COMMENT 'Data about patient from Apollo Hospital'
ROW FORMAT DELIMITED FIELDS TERMINATED BY ','
STORED AS PARQUET 
LOCATION '/user/training/external/data' ;

将数据加载到表中

LOAD DATA LOCAL INPATH 
'/home/cloudera/Desktop/HiveTraining/Dataset/patient_details' INTO TABLE Patient_external;

描述表格

describe formatted Patient_external;



col_name                data_type               comment             

**patientid**               int                                         
name                    string                                      
city                    string                                      
number                  string                                      

Detailed Table Information       
 Database:              default                  
 Owner:                 cloudera                 
 CreateTime:            Mon Mar 25 10:57:23 PDT 2019     
 LastAccessTime:        UNKNOWN                  
 Protect Mode:          None                     
 Retention:             0                        
 Location:          
  hdfs://quickstart.cloudera:8020/user/training/external/data    
 Table Type:            EXTERNAL_TABLE           
 Table Parameters:       
        COLUMN_STATS_ACCURATE   false               
        EXTERNAL                TRUE                
        comment                 Data about patient from Apollo Hospital
        numFiles                0                   
       numRows              -1                  
       rawDataSize          -1                  
     totalSize              0                   
transient_lastDdlTime   1553536643          

  Storage Information        
     SerDe Library:          
      org.apache.hadoop.hive.ql.io.parquet.serde.ParquetHiveSerDe    
     InputFormat:            
          org.apache.hadoop.hive.ql.io.parquet.MapredParquetInputFormat  
     OutputFormat:           
         org.apache.hadoop.hive.ql.io.parquet.MapredParquetOutputFormat

将列名从PatientID更改为Patient_ID

     Alter Table Patient_external change PatientID Patient_ID Int;

现在描述表格

    describe formatted Patient_external;

 col_name               data_type               comment             

**patient_id**              int                                         
name                    string                                      
city                    string                                      
number                  string                                      

Detailed Table Information       
 Database:              default                  
 Owner:                 cloudera                 
 CreateTime:            Mon Mar 25 10:57:23 PDT 2019     
 LastAccessTime:        UNKNOWN                  
 Protect Mode:          None                     
 Retention:             0                        
 Location:          
  hdfs://quickstart.cloudera:8020/user/training/external/data    
 Table Type:            EXTERNAL_TABLE           
 Table Parameters:       
        COLUMN_STATS_ACCURATE   false               
        EXTERNAL                TRUE                
        comment                 Data about patient from Apollo Hospital
        numFiles                0                   
       numRows              -1                  
       rawDataSize          -1                  
     totalSize              0                   
transient_lastDdlTime   1553536643          

  Storage Information        
     SerDe Library:          
      org.apache.hadoop.hive.ql.io.parquet.serde.ParquetHiveSerDe    
     InputFormat:            
          org.apache.hadoop.hive.ql.io.parquet.MapredParquetInputFormat  
     OutputFormat:           
         org.apache.hadoop.hive.ql.io.parquet.MapredParquetOutputFormat

更改包含数据的Hive外部表中的列名

2 个答案: