本文為英文版的機器翻譯版本，如內容有任何歧義或不一致之處，概以英文版為準。
# DESCRIBE
顯示指定資料表的一個或多個資料欄，包括分割區欄位。此指令有助於檢查複雜資料欄的屬性。
## 概要
```
DESCRIBE [EXTENDED | FORMATTED] [db_name.]table_name [PARTITION partition_spec] [col_name ( [.field_name] | [.'$elem$'] | [.'$key$'] | [.'$value$'] )]
```
**重要**
此陳述式的語法是 `DESCRIBE {{table_name}}`，而不是 `DESCRIBE TABLE {{table_name}}`。使用後一種語法會導致錯誤訊息 FAILED: SemanticException [Error 10001]: Table not found table (失敗：SemanticException [Error 10001]：找不到資料表)。
## Parameters
**[EXTENDED \| FORMATTED]**
判斷輸出的格式。省略這些參數會以表格格式顯示資料欄名稱及其對應的資料類型，包括分割區欄位。指定 `FORMATTED` 不僅以表格格式顯示資料欄名稱和資料類型，而且還顯示詳細的資料表和儲存資訊。`EXTENDED` 會以表格格式顯示資料欄和資料類型資訊，並以 Thrift 序列化格式顯示資料表的詳細中繼資料。此格式不易讀取，並且主要用於偵錯。
**[PARTITION partition\_spec]**
如果包含，則會列出由 `partition_spec` 指定之分割區中繼資料，其中 `partition_spec` 的格式為 `(partition_column = partition_col_value, partition_column = partition_col_value, ...)`。
**[col\_name ( [.field\_name] \| [.'$elem$'] \| [.'$key$'] \| [.'$value$'] )\* ]**
指定要檢查的資料欄和屬性。您可以為結構的元素指定 `.field_name`，為陣列元素指定 `'$elem$'`，為對應金鑰指定 `'$key$'`，以及為對應值指定 `'$value$'`。您可以以遞迴的方式指定，以進一步探索複雜的資料欄。
### 範例
```
DESCRIBE orders
```
```
DESCRIBE FORMATTED mydatabase.mytable PARTITION (part_col = 100) columnA;
```
以下查詢和輸出顯示了基於 Amazon EMR 範例資料的 `impressions` 資料表的資料欄和資料類型。
```
DESCRIBE impressions
```
```
requestbegintime string from deserializer
adid string from deserializer
impressionid string from deserializer
referrer string from deserializer
useragent string from deserializer
usercookie string from deserializer
ip string from deserializer
number string from deserializer
processid string from deserializer
browsercokie string from deserializer
requestendtime string from deserializer
timers struct from deserializer
threadid string from deserializer
hostname string from deserializer
sessionid string from deserializer
dt string
# Partition Information
# col_name data_type comment
dt string
```
以下範例查詢和輸出顯示了使用 `FORMATTED` 選項時相同資料表的結果。
```
DESCRIBE FORMATTED impressions
```
```
requestbegintime string from deserializer
adid string from deserializer
impressionid string from deserializer
referrer string from deserializer
useragent string from deserializer
usercookie string from deserializer
ip string from deserializer
number string from deserializer
processid string from deserializer
browsercokie string from deserializer
requestendtime string from deserializer
timers struct from deserializer
threadid string from deserializer
hostname string from deserializer
sessionid string from deserializer
dt string
# Partition Information
# col_name data_type comment
dt string
# Detailed Table Information
Database: sampledb
Owner: hadoop
CreateTime: Thu Apr 23 02:55:21 UTC 2020
LastAccessTime: UNKNOWN
Protect Mode: None
Retention: 0
Location: s3://us-east-1.elasticmapreduce/samples/hive-ads/tables/impressions
Table Type: EXTERNAL_TABLE
Table Parameters:
EXTERNAL TRUE
transient_lastDdlTime 1587610521
# Storage Information
SerDe Library: org.openx.data.jsonserde.JsonSerDe
InputFormat: org.apache.hadoop.mapred.TextInputFormat
OutputFormat: org.apache.hadoop.hive.ql.io.IgnoreKeyTextOutputFormat
Compressed: No
Num Buckets: -1
Bucket Columns: []
Sort Columns: []
Storage Desc Params:
paths requestbegintime, adid, impressionid, referrer, useragent, usercookie, ip
serialization.format 1
```
以下範例查詢和輸出顯示了使用 `EXTENDED` 選項時相同資料表的結果。資料表詳細資訊會在單一行上輸出，但在此處進行格式化以增加可讀性。
```
DESCRIBE EXTENDED impressions
```
```
requestbegintime string from deserializer
adid string from deserializer
impressionid string from deserializer
referrer string from deserializer
useragent string from deserializer
usercookie string from deserializer
ip string from deserializer
number string from deserializer
processid string from deserializer
browsercokie string from deserializer
requestendtime string from deserializer
timers struct from deserializer
threadid string from deserializer
hostname string from deserializer
sessionid string from deserializer
dt string
# Partition Information
# col_name data_type comment
dt string
Detailed Table Information Table(tableName:impressions, dbName:sampledb, owner:hadoop, createTime:1587610521,
lastAccessTime:0, retention:0, sd:StorageDescriptor(cols:[FieldSchema(name:requestbegintime, type:string, comment:null),
FieldSchema(name:adid, type:string, comment:null), FieldSchema(name:impressionid, type:string, comment:null),
FieldSchema(name:referrer, type:string, comment:null), FieldSchema(name:useragent, type:string, comment:null),
FieldSchema(name:usercookie, type:string, comment:null), FieldSchema(name:ip, type:string, comment:null),
FieldSchema(name:number, type:string, comment:null), FieldSchema(name:processid, type:string, comment:null),
FieldSchema(name:browsercokie, type:string, comment:null), FieldSchema(name:requestendtime, type:string, comment:null),
FieldSchema(name:timers, type:struct, comment:null), FieldSchema(name:threadid,
type:string, comment:null), FieldSchema(name:hostname, type:string, comment:null), FieldSchema(name:sessionid,
type:string, comment:null)], location:s3://us-east-1.elasticmapreduce/samples/hive-ads/tables/impressions,
inputFormat:org.apache.hadoop.mapred.TextInputFormat,
outputFormat:org.apache.hadoop.hive.ql.io.IgnoreKeyTextOutputFormat, compressed:false, numBuckets:-1,
serdeInfo:SerDeInfo(name:null, serializationLib:org.openx.data.jsonserde.JsonSerDe, parameters:{serialization.format=1,
paths=requestbegintime, adid, impressionid, referrer, useragent, usercookie, ip}), bucketCols:[], sortCols:[], parameters:{},
skewedInfo:SkewedInfo(skewedColNames:[], skewedColValues:[], skewedColValueLocationMaps:{}),
storedAsSubDirectories:false), partitionKeys:[FieldSchema(name:dt, type:string, comment:null)],
parameters:{EXTERNAL=TRUE, transient_lastDdlTime=1587610521}, viewOriginalText:null, viewExpandedText:null,
tableType:EXTERNAL_TABLE)
```