我有一個樣品蜂房表創建爲蜂巢查詢記錄一個特定uniontype
CREATE TABLE union_test(foo UNIONTYPE<int, double, array<string>, struct<a:int,b:string>>);
的數據可作爲
SELECT foo FROM union_test;
被視爲輸出是
{0:1}
{1:2.0}
{2:["three","four"]}
{3:{"a":5,"b":"five"}}
{2:["six","seven"]}
{3:{"a":8,"b":"eight"}}
{0:9}
{1:10.0}
第一字段（標籤）表示聯合的類型（0表示int，1表示double，2表示數組等）。
我的問題是，如果我發現只選擇那些聯合類型爲2（數組）的記錄，應該如何構造我的查詢？
Hive從UnionType中讀取數據沒有功能。所以我寫了2個UDF。一個獲得聯盟標籤（你試圖做），第二個獲得聯盟的結構作爲例子。
get_union_tag（）函數：
package HiveUDF;
import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDFArgumentException;
import org.apache.hadoop.hive.ql.exec.UDFArgumentLengthException;
import org.apache.hadoop.hive.ql.exec.UDFArgumentTypeException;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.ql.udf.generic.GenericUDF;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.UnionObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorFactory;
@Description(name = "get_union_tag", value = "_FUNC_(unionObject)"
+ " - Returns union object Tag", extended = "Example:\n" + " > SELECT _FUNC_(unionObject) FROM src LIMIT 1;\n one")
public class GetUnionTag extends GenericUDF {
// Global variables that inspect the input.
// These are set up during the initialize() call, and are then used during the
// calls to evaluate()
private transient UnionObjectInspector uoi;
@Override
// This is what we do in the initialize() method:
// Verify that the input is of the type expected
// Set up the ObjectInspectors for the input in global variables
// Return the ObjectInspector for the output
public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumentException {
// Verify the input is of the required type.
// Set the global variables (the various ObjectInspectors) while we're doing this
// Exactly one input argument
if(arguments.length != 1){
throw new UDFArgumentLengthException("_FUNC_(unionObject) accepts exactly one argument.");
}
// Is the input an array<>
if(arguments[0].getCategory() != ObjectInspector.Category.UNION){
throw new UDFArgumentTypeException(0,"The single argument to AddExternalIdToPurchaseDetails should be "
+ "Union<>"
+ " but " + arguments[0].getTypeName() + " is found");
}
// Store the ObjectInspectors for use later in the evaluate() method
uoi = ((UnionObjectInspector)arguments[0]);
// Set up the object inspector for the output, and return it
return PrimitiveObjectInspectorFactory.javaByteObjectInspector;
}
@Override
public Object evaluate(DeferredObject[] arguments) throws HiveException {
byte tag = uoi.getTag(arguments[0].get());
return tag;
}
@Override
public String getDisplayString(String[] children) {
StringBuilder sb = new StringBuilder();
sb.append("get_union_tag(");
for (int i = 0; i < children.length; i++) {
if (i > 0) {
sb.append(',');
}
sb.append(children[i]);
}
sb.append(')');
return sb.toString();
}
}
功能get_struct_from_union（）UDF：
package HiveUDF;
import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDFArgumentException;
import org.apache.hadoop.hive.ql.exec.UDFArgumentLengthException;
import org.apache.hadoop.hive.ql.exec.UDFArgumentTypeException;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.ql.udf.generic.GenericUDF;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.StructObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.UnionObjectInspector;
@Description(name = "get_union_struct", value = "_FUNC_(unionObject)"
+ " - Returns struct ", extended = "Example:\n" + " > _FUNC_(unionObject).value \n 90.0121")
public class GetUnionStruct extends GenericUDF {
// Global variables that inspect the input.
// These are set up during the initialize() call, and are then used during the
// calls to evaluate()
//
// ObjectInspector for the list (input array<>)
// ObjectInspector for the struct<>
// ObjectInspectors for the elements of the struct<>, target, quantity and price
private UnionObjectInspector unionObjectInspector;
private StructObjectInspector structObjectInspector;
@Override
// This is what we do in the initialize() method:
// Verify that the input is of the type expected
// Set up the ObjectInspectors for the input in global variables
// Return the ObjectInspector for the output
public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumentException {
// Verify the input is of the required type.
// Set the global variables (the various ObjectInspectors) while we're doing this
// Exactly one input argument
if(arguments.length != 1){
throw new UDFArgumentLengthException("_FUNC_(unionObject) accepts exactly one argument.");
}
// Is the input an array<>
if(arguments[0].getCategory() != ObjectInspector.Category.UNION){
throw new UDFArgumentTypeException(0,"The single argument to AddExternalIdToPurchaseDetails should be "
+ "Union<Struct>"
+ " but " + arguments[0].getTypeName() + " is found");
}
// Set up the object inspector for the output, and return it
return structObjectInspector;
}
@Override
public Object evaluate(DeferredObject[] arguments) throws HiveException {
return ((UnionObjectInspector) unionObjectInspector).getField(arguments[0].get());
}
@Override
public String getDisplayString(String[] children) {
StringBuilder sb = new StringBuilder();
sb.append("get_union_vqtstruct(");
for (int i = 0; i < children.length; i++) {
if (i > 0) {
sb.append(',');
}
sb.append(children[i]);
}
sb.append(')');
return sb.toString();
}
}
使用這些UDF's編譯和創建JAR文件。比上傳到配置單元（在我的情況下HDInsight）。不僅僅是使用
add jar wasb:///hive/HiveGUDF.jar;
CREATE TEMPORARY FUNCTION get_union_struct AS 'HiveUDF.GetUnionStruct';
SELECT get_union_tag(exposed) FROM test;