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1. Add Apache incubator disclaimer. 2. Add "Edit on Github" button on every page. 3. Add Committer Ling Miao. 4. Modify some English documents.
1.8 KiB
1.8 KiB
#BITMAP
description
Syntax
TO_BITMAP(expr) : Convert TINYINT,SMALLINT,INT type column to Bitmap.
BITMAP_UNION(expr) : Calculate the union of Bitmap, return the serialized Bitmap value.
BITMAP_COUNT(expr) : Calculate the distinct value number of a Bitmap.
BITMAP_UNION_INT(expr) : Calculate the distinct value number of TINYINT,SMALLINT and INT type column. Same as COUNT(DISTINCT expr)
Notice：
1. TO_BITMAP function only receives TINYINT,SMALLINT,INT.
2. BITMAP_UNION only receives following types of parameter:
- Column with BITMAP_UNION aggregate type in AGGREGATE KEY mode.
- TO_BITMAP function.
example
CREATE TABLE `bitmap_udaf` (
`id` int(11) NULL COMMENT "",
`id2` int(11)
) ENGINE=OLAP
DUPLICATE KEY(`id`)
DISTRIBUTED BY HASH(`id`) BUCKETS 10;
mysql> select bitmap_count(bitmap_union(to_bitmap(id2))) from bitmap_udaf;
+----------------------------------------------+
| bitmap_count(bitmap_union(to_bitmap(`id2`))) |
+----------------------------------------------+
| 6 |
+----------------------------------------------+
mysql> select bitmap_union_int (id2) from bitmap_udaf;
+-------------------------+
| bitmap_union_int(`id2`) |
+-------------------------+
| 6 |
+-------------------------+
CREATE TABLE `bitmap_test` (
`id` int(11) NULL COMMENT "",
`id2` varchar(0) bitmap_union NULL // NOTICE: bitmap_union's varchar length must be 0.
) ENGINE=OLAP
AGGREGATE KEY(`id`)
DISTRIBUTED BY HASH(`id`) BUCKETS 10;
mysql> select bitmap_count(bitmap_union(id2)) from bitmap_test;
+-----------------------------------+
| bitmap_count(bitmap_union(`id2`)) |
+-----------------------------------+
| 8 |
+-----------------------------------+
keyword
BITMAP,BITMAP_COUNT,BITMAP_UNION,BITMAP_UNION_INT,TO_BITMAP