BITMAP_CARDINALITY Function

Function Description

The BITMAP_CARDINALITY function is used to calculate the number of elements in a bitmap type. This function accepts a bitmap type parameter and returns a bigint type value representing the number of elements in the bitmap.

Parameter Description

• bitmap: The input bitmap type data.

Return Result

• Returns a bigint type value representing the number of elements in the bitmap.

Usage Example

1. Calculate the number of elements in a single bitmap:

<Notes> </Notes> <permalink> </permalink> ```sql SELECT bitmap_cardinality(bitmap_build(ARRAY[1, 2, 3, 4, 5])); ``` Result: ``` 5 ``` In the above example, we used the `bitmap_build` function to create a bitmap containing 1 to 5, and used the `bitmap_cardinality` function to calculate the number of elements in the bitmap, which is 5.

2. Calculate the number of elements after combining multiple bitmaps:

   SELECT bitmap_cardinality(bitmap_union(bitmap_build(ARRAY[1, 2]), bitmap_build(ARRAY[3, 4])));
   

Result:

4

In this example, we created two bitmaps separately, one containing 1 and 2, and the other containing 3 and 4. Then we used the bitmap_union function to merge these two bitmaps, and finally used the bitmap_cardinality function to calculate the number of elements in the merged bitmap, which is 4.

3. Calculate the number of elements in the intersection of two bitmaps:

   SELECT bitmap_cardinality(bitmap_intersect(bitmap_build(ARRAY[1, 2, 3]), bitmap_build(ARRAY[2, 3, 4])));
   

Result:

2

In this example, we created two bitmaps, one containing 1, 2, and 3, and the other containing 2, 3, and 4. Using the bitmap_intersect function, we calculate the intersection of the two bitmaps, and then use the bitmap_cardinality function to calculate the number of elements in the intersection result, which is 2.

Through the above example, you can better understand the usage and scenarios of the BITMAP_CARDINALITY function. In practical applications, you can create and manipulate bitmap type data as needed, and use this function to calculate the number of elements.