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What is SerDe and how to write a SerDe? ------------------------ Please refer to http://wiki.apache.org/hadoop/Hive/DeveloperGuide Section SerDe. How to load data into Hive ------------------------ In order to load data into Hive, we need to tell Hive the format of the data through "CREATE TABLE" statement: * FileFormat: the data has to be in Text or SequenceFile. * Format of the row: * If the data is in delimited format, use MetadataTypedColumnsetSerDe * If the data is a serialized thrift object, use ThriftSerDe The steps to load the data: 1 Create a table: CREATE TABLE t (foo STRING, bar STRING) ROW FORMAT DELIMITED FIELDS TERMINATED BY '\t' STORED AS TEXTFILE; CREATE TABLE t2 (foo STRING, bar ARRAY<STRING>) ROW FORMAT DELIMITED FIELDS TERMINATED BY '\t' COLLECTION ITEMS TERMINATED BY ',' STORED AS TEXTFILE; CREATE TABLE t3 (foo STRING, bar MAP<STRING,STRING>) ROW FORMAT DELIMITED FIELDS TERMINATED BY '\t' COLLECTION ITEMS TERMINATED BY ',' MAP KEYS TERMINATED BY ':' STORED AS TEXTFILE; CREATE TABLE t4 (foo STRING, bar MAP<STRING,STRING>) ROW FORMAT SERIALIZER 'org.apache.hadoop.hive.serde2.MetadataTypedColumnsetSerDe' WITH SERDEPROPERTIES ('columns'='foo,bar','SERIALIZATION.FORMAT'='9'); (RegexDeserializer is not done yet) CREATE TABLE t5 (foo STRING, bar STRING) ROW FORMAT SERIALIZER 'org.apache.hadoop.hive.serde2.RegexDeserializer' WITH SERDEPROPERTIES ('regex'='([a-z]*) *([a-z]*)'); 2 Load the data: LOAD DATA LOCAL INPATH '../examples/files/kv1.txt' OVERWRITE INTO TABLE t; How to read data from Hive tables ------------------------ In order to read data from Hive tables, we need to know the same 2 things: * File Format * Row Format Then we just need to directly open the HDFS file and read the data.
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