Merge pull request #370 from HrishiDhondge/main

Code for SQL-435 issue

Author: xaeldung

sql-queries-12/combine-distinct-count-in-SQL/distinct-count-for-multiple-columns.sql

@@ -0,0 +1,13 @@
+-- Only for MySQL and SQL Server --
+SELECT COUNT(DISTINCT textbook, credits) AS unique_count FROM Course;
+
+-- Only for PostgreSQL --
+SELECT COUNT(DISTINCT(textbook, credits)) AS unique_count FROM Course;
+
+-- Works for MySQL, PostgreSQL, and SQL Server --
+-- Using Subquery --
+SELECT COUNT(*) AS unique_count FROM (SELECT DISTINCT textbook, credits FROM Course) temp_course;
+
+-- Using CONCAT function --
+SELECT COUNT(DISTINCT CONCAT(textbook, '--', credits)) AS unique_count FROM Course;
+SELECT COUNT(DISTINCT CONCAT(textbook, '--', credits)) AS unique_count FROM Course WHERE department_id = 4;

sql-queries-12/combine-distinct-count-in-SQL/distinct-count-for-single-column.sql

@@ -0,0 +1,2 @@
+SELECT COUNT(DISTINCT textbook) FROM Course;
+SELECT COUNT(DISTINCT textbook) AS unique_textbook_count FROM Course;