[fix] Remove count function

docs/content/primary-key-table/merge-engine/aggregation.md

@@ -71,8 +71,14 @@ Current supported aggregate functions and data types are:
   It supports DECIMAL, TINYINT, SMALLINT, INTEGER, BIGINT, FLOAT, and DOUBLE data types.
 
 ### count
-  The count function counts the values across multiple rows.
-  It supports INTEGER, BIGINT data types.
+  In scenarios where counting rows that match a specific condition is required, you can use the SUM function to achieve this. By expressing a condition as a Boolean value (TRUE or FALSE) and converting it into a numerical value, you can effectively count the rows. In this approach, TRUE is converted to 1, and FALSE is converted to 0.
+
+  For example, if you have a table orders and want to count the number of rows that meet a specific condition, you can use the following query:
+  ```sql
+  SELECT SUM(CASE WHEN condition THEN 1 ELSE 0 END) AS count
+  FROM orders;
+  ```
+
 
 ### max
   The max function identifies and retains the maximum value.
@@ -260,7 +266,7 @@ For streaming queries, `aggregation` merge engine must be used together with `lo
 
 ## Retraction
 
-Only `sum`, `product`, `count`, `collect`, `merge_map`, `nested_update`, `last_value` and `last_non_null_value` supports retraction (`UPDATE_BEFORE` and `DELETE`), others aggregate functions do not support retraction.
+Only `sum`, `product`, `collect`, `merge_map`, `nested_update`, `last_value` and `last_non_null_value` supports retraction (`UPDATE_BEFORE` and `DELETE`), others aggregate functions do not support retraction.
 If you allow some functions to ignore retraction messages, you can configure:
 `'fields.${field_name}.ignore-retract'='true'`.
 

paimon-core/src/main/java/org/apache/paimon/mergetree/compact/aggregate/FieldAggregator.java

@@ -89,9 +89,6 @@ public static FieldAggregator createFieldAggregator(
                     case FieldFirstNonNullValueAgg.LEGACY_NAME:
                         fieldAggregator = new FieldFirstNonNullValueAgg(fieldType);
                         break;
-                    case FieldCountAgg.NAME:
-                        fieldAggregator = new FieldCountAgg(fieldType);
-                        break;
                     case FieldProductAgg.NAME:
                         fieldAggregator = new FieldProductAgg(fieldType);
                         break;

paimon-core/src/test/java/org/apache/paimon/mergetree/compact/aggregate/FieldAggregatorTest.java

@@ -156,37 +156,6 @@ public void testFieldSumIntAgg() {
         assertThat(fieldSumAgg.retract(null, 5)).isEqualTo(-5);
     }
 
-    @Test
-    public void testFieldCountIntAgg() {
-        FieldCountAgg fieldCountAggInt = new FieldCountAgg(new IntType());
-        assertThat(fieldCountAggInt.agg(null, null)).isEqualTo(0);
-        assertThat(fieldCountAggInt.agg(1, null)).isEqualTo(1);
-        assertThat(fieldCountAggInt.agg(null, 15)).isEqualTo(1);
-        assertThat(fieldCountAggInt.agg(1, 0)).isEqualTo(2);
-        assertThat(fieldCountAggInt.agg(3, 6)).isEqualTo(4);
-
-        FieldCountAgg fieldCountAggLong = new FieldCountAgg(new BigIntType());
-        assertThat(fieldCountAggLong.agg(null, null)).isEqualTo(0L);
-        assertThat(fieldCountAggLong.agg((long) 1, null)).isEqualTo((long) 1);
-        assertThat(fieldCountAggLong.agg(null, (long) 15)).isEqualTo(1L);
-        assertThat(fieldCountAggLong.agg((long) 1, 0)).isEqualTo((long) 2);
-        assertThat(fieldCountAggLong.agg((long) 3, (long) 6)).isEqualTo((long) 4);
-
-        FieldCountAgg fieldCountAggByte = new FieldCountAgg(new TinyIntType());
-        assertThat(fieldCountAggByte.agg(null, null)).isEqualTo((byte) 0);
-        assertThat(fieldCountAggByte.agg((byte) 1, null)).isEqualTo((byte) 1);
-        assertThat(fieldCountAggByte.agg(null, (byte) 15)).isEqualTo((byte) 1);
-        assertThat(fieldCountAggByte.agg((byte) 1, 0)).isEqualTo((byte) 2);
-        assertThat(fieldCountAggByte.agg((byte) 3, (byte) 6)).isEqualTo((byte) 4);
-
-        FieldCountAgg fieldCountAggShort = new FieldCountAgg(new SmallIntType());
-        assertThat(fieldCountAggShort.agg(null, null)).isEqualTo((short) 0);
-        assertThat(fieldCountAggShort.agg((short) 1, null)).isEqualTo((short) 1);
-        assertThat(fieldCountAggShort.agg(null, (short) 15)).isEqualTo((short) 1);
-        assertThat(fieldCountAggShort.agg((short) 1, 0)).isEqualTo((short) 2);
-        assertThat(fieldCountAggShort.agg((short) 3, (short) 6)).isEqualTo((short) 4);
-    }
-
     @Test
     public void testFieldProductIntAgg() {
         FieldProductAgg fieldProductAgg = new FieldProductAgg(new IntType());