UNIQ

Syntax

UNIQ(expr)

Purpose

This function is used to approximately calculate the number of distinct values in a column.

Examples

1. Enable the ClickHouse extension function mode.

   obclient> ALTER SYSTEM SET sql_func_extension_mode = "ClickHouse";
   

2. Create a test table test_tbl1.

   obclient> CREATE TABLE test_tbl1 (col1 INT PRIMARY KEY, col2 VARCHAR(50), col3 INT);
   

3. Insert data into the table test_tbl1.

   obclient> INSERT INTO test_tbl1 VALUES(1, 'a1', 6), (2, 'a2', 8), (3, 'a2', 8);
   

4. Use the UNIQ function to calculate the number of distinct values in the col3 column.

   obclient> SELECT UNIQ(col3) FROM test_tbl1;
   

   The returned result is as follows:

   +------------+
   | UNIQ(col3) |
   +------------+
   |          2 |
   +------------+
   1 row in set