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Database Articles
Page 264 of 547
How can we nest a subquery within another subquery?
If a subquery is nested inside another subquery then it is called a nested subquery. To make it understand we are creating the nested subquery from the following tables data −mysql> Select * from Cars; +------+--------------+---------+ | ID | Name | Price | +------+--------------+---------+ | 1 | Nexa | 750000 | | 2 | Maruti Swift | 450000 | | 3 | BMW ...
Read MoreWhat are single row and multiple row subqueries?
Single Row Sub QueryA single-row subquery is used when the outer query's results are based on a single, unknown value. Although this query type is formally called "single-row, " the name implies that the query returns multiple columns-but only one row of results. However, a single-row subquery can return only one row of results consisting of only one column to the outer query.In the below SELECT query, inner MySQL returns only one row i.e. the minimum salary for the company. It, in turn, uses this value to compare the salary of all the employees and displays only those, whose salary ...
Read MoreWhat are the synonym statements of MySQL DESCRIBE?
Followings are the synonyms statements of MySQL DESCRIBE i.e. the statements with the help of which we can get the same kind of information/structure of the table as we get from DESCRIBE −EXPLAIN StatementEXPLAIN is the synonym of the DESCRIBE statement. Its syntax is also similar to the DESCRIBE statement. Consider the following example −mysql> Explain Employee; +-------+-------------+------+-----+---------+------------------+ | Field | Type | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+------------------+ | ID | int(11) | NO | PRI | NULL | auto_increment | | ...
Read MoreHow can we sort multiple columns in a single query?
We can sort multiple columns in a single query by giving more than one column name with ORDER BY Clause. The syntax of the above is as follows −SyntaxSelect Col1, Col2, … from table_name ORDER BY Col1, Col2, …ExampleSuppose we want to sort the table named ‘Student’ by columns ‘Name’ and ‘RollNo’ both then we can write the single query for this as follows −mysql> Select Name, RollNo from student order by name, rollno; +--------+--------+ | name | rollno | +--------+--------+ | Aarav | 150 | | Aryan | 165 ...
Read MoreHow can we amend the declared size of a column's data type in MySQL?
It can be done with the help of ALTER TABLE command of MySQL. Consider the table ‘Student’ in which the size of ‘Grade’ column is declared as Varchar(10), can be seen from the following query −mysql> DESCRIBE Student; +--------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------+-------------+------+-----+---------+-------+ | Name | varchar(20) | YES | | NULL | | | RollNo | int(11) | YES | ...
Read MoreHow can we combine ROW selection with COLUMN selection in MySQL?
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 MoreWhat is MySQL LOAD DATA statement?
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 MoreWhat kind of information is displayed by MySQL DESCRIBE statement?
The DESCRIBE statement gives information about MySQL table’s structure.ExampleConsider the constructing of the following table name ‘Employee’ with Create Table statement as follows −mysql> Create table Employee(ID INT NOT NULL PRIMARY KEY AUTO_INCREMENT, Name Varchar(20)); Query OK, 0 rows affected (0.20 sec)Now with the help of ‘DESCRIBE Employee‘ statement, we can get the information about the employee table.mysql> Describe Employee; +-------+-------------+------+-----+---------+------------------+ | Field | Type | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+------------------+ | ID | int(11) | NO | PRI | NULL | auto_increment ...
Read MoreWhat is the use of comparison operators with MySQL subquery?
The subquery can return at most one value. The value can be the result of an arithmetic expression or a column function. MySQL then compares the value that results from the subquery with the value on the other side of the comparison operator. MySQL subquery can be used before or after any of the comparison operators like =, >, >=,
Read MoreHow can we use a subquery that contains a reference to a table that also appears in the outer query?
A subquery that contains a reference to a table that also appears in the outer query is called a correlated subquery. In this case, MySQL evaluates from inner query to the outer query. To understand it we are having the following data from table ‘cars’ −mysql> Select * from Cars; +------+--------------+---------+ | ID | Name | Price | +------+--------------+---------+ | 1 | Nexa | 750000 | | 2 | Maruti Swift | 450000 | | 3 | BMW | 4450000 | | 4 ...
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