MySQL Articles - Page 369 of 439

For sorting the rows in a meaningful way we can use ORDER BY clause. Suppose we want to sort the rows of the following table −mysql> Select * from Student; +--------+--------+--------+ | Name   | RollNo | Grade  | +--------+--------+--------+ | Gaurav |    100 | B.tech | | Aarav  |    150 | M.SC   | | Aryan  |    165 | M.tech | +--------+--------+--------+ 3 rows in set (0.00 sec)The query below sorted the table by ‘Name’.mysql> Select * from student order by name; +--------+--------+--------+ | Name   | RollNo | Grade  | +--------+--------+--------+ | Aarav  |   ... Read More

For combining ROW selection with COLUMN selection, we can use the ‘WHERE’ clause. For example, we have a table below −mysql> Select * from Student; +--------+--------+--------+ | Name   | RollNo | Grade  | +--------+--------+--------+ | Gaurav | 100    | B.tech | | Aarav  | 150    | M.SC   | | Aryan  | 165    | M.tech | +--------+--------+--------+ 3 rows in set (0.00 sec)Now, the following query will show how we can combine ROW selection with COLUMN selection using WHERE clause.mysql> Select Name, RollNo, Grade from Student where Grade='M.Sc' or Grade='B.Tech'; +--------+--------+--------+ | Name   | RollNo ... Read More

LOAD DATAThis statement is used for importing the data from data files into our database. It reads data records directly from a file and inserts them into a table. Its syntax would be as follows −SyntaxLOAD DATA LOCAL INFILE '[path/][file_name]' INTO TABLE [table_name ];Here, a path is the address of the file.file_name is the name of the .txt filetable_name is the table where the data will be loaded.To illustrate the concept we are having the following data, separated by tab, in ‘A.txt’ whose path is d:/A.txt −100 John USA 10000 101 Paul UK 12000 102 Henry NZ 11000 103 Rick ... Read More

Suppose we have the following table named stock_item in which the column quantity is having duplicate values i.e. for item name ‘Notebooks’ and ‘Pencil’, the column ‘Quantity’ is having duplicate values ‘40’ and for items ‘Shirts’, ‘Shoes’ and ‘Trousers’ triplicate value 29 is hold by column ‘quantity’ as shown in the table.mysql> Select * from stock_item; +------------+----------+ | item_name  |quantity  | +------------+----------+ | Calculator | 89       | | Notebooks  | 40       | | Pencil     | 40       | | Pens       | 32       | | ... Read More

Suppose we have the following table named stock_item in which the column quantity is having duplicate values i.e. for item name ‘Notebooks’ and ‘Pencil’, the column ‘Quantity’ is having duplicate values ‘40’ and for items ‘Shirts’, ‘Shoes’ and ‘Trousers’ triplicate value 29 is hold by column ‘quantity’ as shown in the table.mysql> Select * from stock_item; +------------+----------+ | item_name  |quantity  | +------------+----------+ | Calculator |       89 | | Notebooks  |       40 | | Pencil     |       40 | | Pens       |       32 | | ... Read More

MySQL scalar subquery returns exactly one column value from one row and we can use it where a single column is permissible. Followings are the cases when scalar subqueries return value other than one row −Case1 − When it returns 0 rowsIn case if the subquery returns 0 rows then the value of scalar subquery expression would be NULL.Case2 − When it returns more than one rowsIn case if the subquery returns more than one row then, due to the property of scalar subquery, MySQL returns an error.It can be understood with the help of an example which uses the ... Read More

Following is a procedure that counts the number of rows get affected by MySQL query −mysql> Delimiter // mysql> CREATE PROCEDURE `query`.`row_cnt` (IN command VarChar(60000))     -> BEGIN     -> SET @query = command;     -> PREPARE stmt FROM @query;     -> EXECUTE stmt;     -> SELECT ROW_COUNT() AS 'Affected rows';     -> END // Query OK, 0 rows affected (0.00 sec) mysql> Delimiter ; mysql> Create table Testing123(First Varchar(20), Second Varchar(20)); Query OK, 0 rows affected (0.48 sec) mysql> CALL row_cnt("INSERT INTO testing123(First,Second) Values('Testing First','Testing Second');"); +---------------+ | Affected rows | +---------------+ | 1             | +---------------+ 1 row in set (0.10 sec) Query OK, 0 rows affected (0.11 sec)

A subquery is best defined as a query within a query. Subqueries enable you to write queries that select data rows for criteria that are actually developed while the query is executing at runtime. More formally, it is the use of a SELECT statement inside one of the clauses of another SELECT statement. In fact, a subquery can be contained inside another subquery, which is inside another subquery, and so forth. A subquery can also be nested inside INSERT, UPDATE, and DELETE statements. Subqueries must be enclosed within parentheses.A subquery can be used any place where an expression is allowed ... Read More

With the help of the following query we can create a stored procedure to generate five random numbers −mysql> DELIMITER // mysql> DROP PROCEDURE IF EXISTS RandomNumbers;     -> CREATE PROCEDURE RandomNumbers()     -> BEGIN     -> SET @i = 0;     -> REPEAT     -> SELECT RAND() AS 'Random Number';     -> SET @i = @i + 1;     -> UNTIL @i >=5 END REPEAT;     -> END     -> // Query OK, 0 rows affected (0.16 sec) Query OK, 0 rows affected (0.16 sec)Now, invoke the procedure to ... Read More

If we have ALTER ROUTINE privileges then with the help of DROP FUNCTION statement, we can delete a MySQL stored function. Its syntax can be as follows −SyntaxDROP FUNCTION [IF EXISTS] function_nameHere function_name is the name of the function which we want to delete from our database.Examplemysql> DROP FUNCTION if exists Hello1; Query OK, 0 rows affected (0.70 sec)Now after deleting the function, check for the CREATE FUNCTION statement and we will get the error as follows −mysql> SHOW CREATE FUNCTION Hello1; ERROR 1305 (42000): Function Hello1 does not exist.