Filtering Data in Apache HBase using JAVA API
FILTERING ROWS BASED ON A CONDITION.
FILTER ALLOWS US TO CONTROL WHAT DATA IS RETRIEVED BY SCAN
HBASE PROVIDES A LARGE NUMBER OF BUILT IN FILTERS
FILTER:
CAN RETURN SPECIFIC SET OF ROW IDs.
SPECIFIC SET OF COL/COL FAMILIES
TIMESTAMPS
SPECIFIC VALUE FOR A COL.
AND MANY MORE....
ALL FILTERS ARE SUBCLASSES OF FILTER ABSTRACT CLASS.
ROW FILTER : (CHECK IF ROW ID MATCHES SPECIFIED CONDITION)
ONE OF THE BUILT-IN FILTERS PROVIDED BY HBASE.
ROW FILTER DESCENDS FROM COMPARE FILTER.
FILTER (BASE CLASS) == FILTERBASE == COMPAREFILTER == ROWFILTER
COMPARE FILTER REQUIRES 2 PARAMETERS.
1. OPERATOR
2. COMPARATOR OBJECT
COMPAREFILTER CLASS PROVIDES FEW OPERATORS :
LESS,LESS_OR_EQUAL,EQUAL,NOT_EQUAL,GREATER_OR_EQUAL,GREATER
COMPARATOR OBJECT
THESE ARE THE OBJECTS WHICH WILL COMPARE THE TABLE DATA AGAINST A SPECIFIED VALUE
ROW FILTER WILL TAKE THE OPERATOR AND COMPARATOR OBJECT AND USE THEM TO FILTER ROW IDs
Filter filter = new RowFilter(CompareFilter.CompareOp.EQUAL,
new BinaryComparator(Bytes.toBytes("1")));
CompareFilter.CompareOp.EQUAL == operator
new BinaryComparator(Bytes.toBytes("1"))); == comparator object
//This filter will check if row id matches string "1"
OTHER COMPARATORS AVAILABLE LIKE (FOR COMPARING STRINGS)
REGEXSTRING
SUBSTRING
AT LAST PASS IT TO SET FILTER METHOD OF SCAN OBJECT
Scan userScan = new Scan();
userScan.setFilter(filter); //Scan objects have a setFilter method where we can specify a filter
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