SQL-183: Deleting All Records Except the Top or Bottom N in SQL

sql-queries-3/delete-records-except-top-or-bottom-N/user-defined-variable-in-mysql.sql

@@ -0,0 +1,24 @@
+SET @row_number = 0;
+
+DELETE FROM Student
+WHERE id NOT IN (
+    SELECT id FROM (
+        SELECT id, (@row_number := @row_number + 1) AS row_num
+        FROM Student
+        ORDER BY id
+    ) AS numbered
+    WHERE row_num <= 15
+);
+
+SET @row_number = 0;
+
+DELETE FROM Student
+WHERE id NOT IN (
+    SELECT id FROM (
+        SELECT id, (@row_number := @row_number + 1) AS row_num
+        FROM Student
+        ORDER BY id DESC
+    ) AS numbered
+    WHERE row_num <= 5
+);
+

sql-queries-3/delete-records-except-top-or-bottom-N/using-CTE-sql-server.sql

@@ -0,0 +1,19 @@
+WITH TopStudents AS (
+    SELECT id
+    FROM Student
+    ORDER BY id
+    OFFSET 0 ROWS
+    FETCH NEXT 10 ROWS ONLY
+)
+DELETE FROM Student
+WHERE id NOT IN (SELECT id FROM TopStudents);
+
+WITH BottomStudents AS (
+    SELECT id
+    FROM Student
+    ORDER BY id DESC
+    OFFSET 0 ROWS
+    FETCH NEXT 5 ROWS ONLY
+)
+DELETE FROM Student
+WHERE id NOT IN (SELECT id FROM BottomStudents);

sql-queries-3/delete-records-except-top-or-bottom-N/using-CTE.sql

@@ -0,0 +1,21 @@
+WITH TopStudents AS (
+    SELECT id
+    FROM Student
+    ORDER BY id
+    LIMIT 5
+)
+DELETE FROM Student
+WHERE id NOT IN (SELECT id FROM TopStudents);
+
+SELECT * FROM Student;
+
+WITH BottomStudents AS (
+    SELECT id
+    FROM Student
+    ORDER BY id DESC
+    LIMIT 5
+)
+DELETE FROM Student
+WHERE id NOT IN (SELECT id FROM BottomStudents);
+
+SELECT * FROM Student;

sql-queries-3/delete-records-except-top-or-bottom-N/using-subqueries.sql

@@ -0,0 +1,15 @@
+DELETE FROM Course
+WHERE id NOT IN (
+    SELECT id
+    FROM Course
+    ORDER BY id
+    LIMIT 10
+);
+
+DELETE FROM Course
+WHERE id NOT IN (
+    SELECT id
+    FROM Course
+    ORDER BY id DESC
+    LIMIT 5
+);

sql-queries-3/delete-records-except-top-or-bottom-N/using-window-func.sql

@@ -0,0 +1,21 @@
+WITH NumberedStudents AS (
+    SELECT id, ROW_NUMBER() OVER (ORDER BY id) AS row_num
+    FROM Student
+)
+DELETE FROM Student
+WHERE id NOT IN (
+    SELECT id
+    FROM NumberedStudents
+    WHERE row_num > 10
+);
+
+WITH NumberedStudents AS (
+    SELECT id, ROW_NUMBER() OVER (ORDER BY id DESC) AS row_num
+    FROM Student
+)
+DELETE FROM Student
+WHERE id NOT IN (
+    SELECT id
+    FROM NumberedStudents
+    WHERE row_num > 5
+);