Merge pull request #362 from dvohra09/main

SQL-503 How to interpret and fix the MySQL Error 1093

Author: jzheaux

sql-queries-11/how-to-interpret-and-fix-the-MySQL-Error-1093/fix-when-using-DELETE-statement.sql

@@ -0,0 +1,36 @@
+
+-- This statement generates the Error 1093
+DELETE FROM Program 
+WHERE start_date > 
+(SELECT MIN(start_date) FROM Program);
+
+-- This statement fixes the Error 1093 in the preceding example using a derived table
+DELETE FROM Program
+WHERE start_date > (
+  SELECT subquery_program.start_date
+  FROM (
+    SELECT MIN(start_date) AS start_date FROM Program
+  ) AS subquery_program
+);
+
+
+-- This set of statements fixes the Error 1093 in the example using a temporary table
+- Create a temporary table 
+CREATE TEMPORARY TABLE temp_min_start_date AS
+SELECT MIN(start_date) AS min_date
+FROM Program;
+
+-- Delete from the main table using the temporary table
+DELETE FROM Program
+WHERE start_date > 
+(SELECT min_date FROM temp_min_start_date);
+
+-- Drop the temporary table
+DROP TEMPORARY TABLE temp_min_start_date;
+
+-- This statement fixes the Error 1093 using a join with a derived table
+DELETE p
+FROM Program AS p
+JOIN (SELECT MIN(start_date) AS min_start_date FROM Program) 
+AS min_program_date
+ON p.start_date > min_program_date.min_start_date;

sql-queries-11/how-to-interpret-and-fix-the-MySQL-Error-1093/fix-when-using-UPDATE-statement.sql

@@ -0,0 +1,36 @@
+-- This statement generates the Error 1093
+UPDATE Program t 
+SET t.end_date = (SELECT start_date FROM Program WHERE id=t.id);
+
+-- This statement fixes the Error 1093 in the preceding example using a derived table
+UPDATE Program
+SET end_date = (
+  SELECT max_start_date
+  FROM (
+        SELECT MAX(start_date) AS max_start_date 
+        FROM Program
+       ) AS derived_table
+);
+
+-- This set of statements fixes the Error 1093 in the same example using a temporary table
+-- Create a temporary table 
+CREATE TEMPORARY TABLE 
+IF NOT EXISTS temp_table 
+AS SELECT id, start_date 
+FROM Program;
+
+-- Update the main table using the temporary table
+UPDATE Program t 
+JOIN temp_table temp 
+ON t.id = temp.id 
+SET t.end_date = temp.start_date;
+
+-- Drop the temporary table
+DROP TEMPORARY TABLE 
+IF EXISTS temp_table;
+
+-- This statement fixes the Error 1093 using a self-join
+UPDATE Program p1 
+JOIN Program p2 
+ON p1.id = p2.id 
+SET p1.end_date = p2.start_date;