diff --git a/postgres/dataset_full/employee.sql b/postgres/dataset_full/employee.sql
index a179700..443ce04 100644
--- a/postgres/dataset_full/employee.sql
+++ b/postgres/dataset_full/employee.sql
@@ -31,7 +31,8 @@ DROP TABLE IF EXISTS dept_emp,
                      title,
                      salary, 
                      employee, 
-                     department CASCADE;
+                     department,
+					 audit CASCADE;
 
 CREATE TABLE employee (
 	emp_no      SERIAL NOT NULL,
@@ -123,8 +124,9 @@ BEGIN
 END;
 $$ LANGUAGE plpgsql;
 
+-- only log update and delete, otherwise, it will cause too much change.
 CREATE TRIGGER salary_log_trigger
-AFTER INSERT OR UPDATE OR DELETE ON salary
+AFTER UPDATE OR DELETE ON salary
 FOR EACH ROW
 EXECUTE FUNCTION log_dml_operations();
 
@@ -166,4 +168,4 @@ FROM
 \echo 'LOADING salary'
 \i load_salary1.sql
 \i load_salary2.sql
-\i load_salary3.sql
+\i load_salary3.sql
\ No newline at end of file
diff --git a/postgres/dataset_large/employee.sql b/postgres/dataset_large/employee.sql
index 2a63b73..99e1e70 100644
--- a/postgres/dataset_large/employee.sql
+++ b/postgres/dataset_large/employee.sql
@@ -31,7 +31,8 @@ DROP TABLE IF EXISTS dept_emp,
                      title,
                      salary, 
                      employee, 
-                     department CASCADE;
+                     department,
+					 audit CASCADE;
 
 CREATE TABLE employee (
 	emp_no      SERIAL NOT NULL,
@@ -43,6 +44,8 @@ CREATE TABLE employee (
 	PRIMARY KEY (emp_no)
 );
 
+CREATE INDEX idx_employee_hire_date ON employee (hire_date);
+
 CREATE TABLE department (
 	dept_no     TEXT NOT NULL,
 	dept_name   TEXT NOT NULL,
@@ -88,6 +91,45 @@ CREATE TABLE salary (
 	PRIMARY KEY (emp_no, from_date)
 );
 
+CREATE INDEX idx_salary_amount ON salary (amount);
+
+CREATE TABLE audit (
+    id SERIAL PRIMARY KEY,
+    operation TEXT NOT NULL,
+    query TEXT,
+    user_name TEXT NOT NULL,
+    changed_at TIMESTAMPTZ DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE INDEX idx_audit_operation ON audit (operation);
+CREATE INDEX idx_audit_username ON audit (user_name);
+CREATE INDEX idx_audit_changed_at ON audit (changed_at);
+
+CREATE OR REPLACE FUNCTION log_dml_operations() RETURNS TRIGGER AS $$
+BEGIN
+    IF (TG_OP = 'INSERT') THEN
+        INSERT INTO audit (operation, query, user_name)
+        VALUES ('INSERT', current_query(), current_user);
+        RETURN NEW;
+    ELSIF (TG_OP = 'UPDATE') THEN
+        INSERT INTO audit (operation, query, user_name)
+        VALUES ('UPDATE', current_query(), current_user);
+        RETURN NEW;
+    ELSIF (TG_OP = 'DELETE') THEN
+        INSERT INTO audit (operation, query, user_name)
+        VALUES ('DELETE', current_query(), current_user);
+        RETURN OLD;
+    END IF;
+    RETURN NULL;
+END;
+$$ LANGUAGE plpgsql;
+
+-- only log update and delete, otherwise, it will cause too much change.
+CREATE TRIGGER salary_log_trigger
+AFTER UPDATE OR DELETE ON salary
+FOR EACH ROW
+EXECUTE FUNCTION log_dml_operations();
+
 CREATE OR REPLACE VIEW dept_emp_latest_date AS
 SELECT
 	emp_no,
@@ -125,3 +167,5 @@ FROM
 \i load_title.sql
 \echo 'LOADING salary'
 \i load_salary1.sql
+\i load_salary2.sql
+\i load_salary3.sql
diff --git a/postgres/dataset_small/employee.sql b/postgres/dataset_small/employee.sql
index 2a63b73..9ef71e8 100644
--- a/postgres/dataset_small/employee.sql
+++ b/postgres/dataset_small/employee.sql
@@ -31,7 +31,8 @@ DROP TABLE IF EXISTS dept_emp,
                      title,
                      salary, 
                      employee, 
-                     department CASCADE;
+                     department,
+					 audit CASCADE;
 
 CREATE TABLE employee (
 	emp_no      SERIAL NOT NULL,
@@ -43,6 +44,8 @@ CREATE TABLE employee (
 	PRIMARY KEY (emp_no)
 );
 
+CREATE INDEX idx_employee_hire_date ON employee (hire_date);
+
 CREATE TABLE department (
 	dept_no     TEXT NOT NULL,
 	dept_name   TEXT NOT NULL,
@@ -88,6 +91,50 @@ CREATE TABLE salary (
 	PRIMARY KEY (emp_no, from_date)
 );
 
+CREATE INDEX idx_salary_amount ON salary (amount);
+
+CREATE TABLE audit (
+    id SERIAL PRIMARY KEY,
+    operation TEXT NOT NULL,
+    query TEXT,
+    user_name TEXT NOT NULL,
+    changed_at TIMESTAMPTZ DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE INDEX idx_audit_operation ON audit (operation);
+CREATE INDEX idx_audit_username ON audit (user_name);
+CREATE INDEX idx_audit_changed_at ON audit (changed_at);
+
+CREATE OR REPLACE FUNCTION log_dml_operations() RETURNS TRIGGER AS $$
+BEGIN
+    IF (TG_OP = 'INSERT') THEN
+        INSERT INTO audit (operation, query, user_name)
+        VALUES ('INSERT', current_query(), current_user);
+        RETURN NEW;
+    ELSIF (TG_OP = 'UPDATE') THEN
+        INSERT INTO audit (operation, query, user_name)
+        VALUES ('UPDATE', current_query(), current_user);
+        RETURN NEW;
+    ELSIF (TG_OP = 'DELETE') THEN
+        INSERT INTO audit (operation, query, user_name)
+        VALUES ('DELETE', current_query(), current_user);
+        RETURN OLD;
+    END IF;
+    RETURN NULL;
+END;
+$$ LANGUAGE plpgsql;
+
+-- only log update and delete, otherwise, it will cause too much change.
+CREATE TRIGGER salary_log_trigger
+AFTER UPDATE OR DELETE ON salary
+FOR EACH ROW
+EXECUTE FUNCTION log_dml_operations();
+
+CREATE TRIGGER salary_log_trigger
+AFTER INSERT OR UPDATE OR DELETE ON salary
+FOR EACH ROW
+EXECUTE FUNCTION log_dml_operations();
+
 CREATE OR REPLACE VIEW dept_emp_latest_date AS
 SELECT
 	emp_no,
@@ -125,3 +172,5 @@ FROM
 \i load_title.sql
 \echo 'LOADING salary'
 \i load_salary1.sql
+\i load_salary2.sql
+\i load_salary3.sql