Overlay bitmaps for indexing and querying data

A computer system comprising:

• at least one processor;
• at least one non-transitory computer-readable medium storing computer-executable instructions that, when executed by the at least one processor, cause the computer system to execute a method comprising:
• partitioning a table into one or more row groups comprising a number of rows;
• determining, for a particular column of each row group, a plurality of unique values;
• forming a bit map table comprising bit map columns corresponding to each unique value and bit map rows corresponding to the number of rows of the row group, wherein columns of the bit map table correspond to unique values in rows of the particular column, wherein rows of the bit map table comprise one first binary value when a row of the particular column matches a corresponding bit map table column unique value, and wherein column values, for each row of the bit map table, up to the first binary value comprise a second binary value opposite the first binary value and after the first binary value comprise don't care values;
• and
• forming a bit map string comprising successive columns of the bit map table, the bit map string comprising the first and second binary values, but not the don't care values, from each column;
• and
• successively decoding each bit map, wherein each decoded bit map is used to decode a subsequent encoded bit map.

A non-transitory computer-readable medium storing computer-executable instructions that, when executed by at least one processor of a computer system, cause the computer system to execute method comprising:

• partitioning a table into one or more row groups comprising a number of rows;
• determining, for a particular column of each row group, a plurality of unique values;
• forming a bit map table comprising bit map columns corresponding to each unique value and bit map rows corresponding to the number of rows of the row group, wherein columns of the bit map table correspond to unique values in rows of the particular column, wherein rows of the bit map table comprise one first binary value when a row of the particular column matches a corresponding bit map table column unique value, and wherein column values, for each row of the bit map table, up to the first binary value comprise a second binary value opposite the first binary value and after the first binary value comprise don't care values;
• and
• forming a bit map string comprising successive columns of the bit map table, the bit map string comprising the first and second binary values, but not the don't care values, from each column;
• and
• successively decoding each bit map, wherein each decoded bit map is used to decode a subsequent encoded bit map.