配置单元查询特定联合类型的记录

Question

我有一个示例配置单元 table 创建为

CREATE TABLE union_test(foo UNIONTYPE<int, double, array<string>, struct<a:int,b:string>>);

数据可以查看为

SELECT foo FROM union_test;

输出为

{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}

第一个字段（标记）表示联合的类型（0 表示 int，1 表示双精度，2 表示数组等）。

我的问题是，如果我发现 select 只有那些联合类型为 2（数组）的记录，我应该如何构建我的查询？

Answer 1

Hive 中没有从UnionType 读取数据的函数。所以我写了 2 个 UDF。一个是获取 Union 标记（您尝试这样做），第二个是从 union 获取结构作为示例。

get_union_tag() 函数:

 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();
}

}

函数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();
}

}

使用这些 UDF 编译和创建 jar 文件。比上传到配置单元（在我的例子中是 HDInsight）。不仅仅是使用

add jar wasb:///hive/HiveGUDF.jar;
CREATE TEMPORARY FUNCTION get_union_struct AS 'HiveUDF.GetUnionStruct';

在你之前运行例如

SELECT get_union_tag(exposed) FROM test;

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