feat(duckdb-driver): Support countDistinctApprox (#6409)

Author: ovr

packages/cubejs-duckdb-driver/src/DuckDBQuery.ts

@@ -26,4 +26,8 @@ export class DuckDBQuery extends BaseQuery {
   public timeGroupedColumn(granularity: string, dimension: string) {
     return GRANULARITY_TO_INTERVAL[granularity](dimension);
   }
+
+  public countDistinctApprox(sql: string) {
+    return `approx_count_distinct(${sql})`;
+  }
 }

packages/cubejs-schema-compiler/src/adapter/BaseQuery.js

@@ -2029,18 +2029,15 @@ class BaseQuery {
     return evaluateSql;
   }
 
-  // eslint-disable-next-line @typescript-eslint/no-unused-vars
-  hllInit(sql) {
+  hllInit(_sql) {
     throw new UserError('Distributed approximate distinct count is not supported by this DB');
   }
 
-  // eslint-disable-next-line @typescript-eslint/no-unused-vars
-  hllMerge(sql) {
+  hllMerge(_sql) {
     throw new UserError('Distributed approximate distinct count is not supported by this DB');
   }
 
-  // eslint-disable-next-line @typescript-eslint/no-unused-vars
-  hllCardinality(sql) {
+  hllCardinality(_sql) {
     throw new UserError('Distributed approximate distinct count is not supported by this DB');
   }