How do you select data from a table in SQL?

How do you select data a table in SQL?

The SELECT statement is used to select data from a database. The data returned is stored in a result table, called the result-set.

The most commonly used SQL command is SELECT statement. It is used to query the database and retrieve selected data that follow the conditions we want.

In simple words, we can say that the select statement used to query or retrieve data from a table in the database.

Select table syntax:

SELECT expressions FROM tables WHERE conditions;

select table output:

SQL SELECT COUNT

The SQL COUNT() is a function that returns the number of records of the table in the output. This function is used with the SQL SELECT statement

Let's take a simple example: If you have a record of the voters in the selected area and want to count the number of voters, then it is very difficult to do it manually, but you can do it easily by using SQL SELECT COUNT query.

Syntax of Select Count Function in SQL

SELECT COUNT(column_name) FROM table_name;

In the syntax, we have to specify the column's name after the COUNT keyword and the name of the table on which the Count function is to be executed.

select Count table output:

SQL SELECT TOP

The SELECT TOP statement in SQL shows the limited number of records or rows from the database table. The TOP clause in the statement specifies how many rows are returned.

It shows the top N number of rows from the tables in the output. This clause is used when there are thousands of records stored in the database tables.

Syntax of TOP Clause in SQL

SELECT TOP number | percent column_Name1, column_Name2, ....., column_NameN FROM table_name WHERE [Condition] ;

select Top table output:

SQL SELECT FIRST

The SQL first() function is used to return the first value of the selected column. Let's see the syntax of sql select first() function:

Select First table syntax:

SELECT FIRST(column_name) FROM table_name;

select First table output:

SQL SELECT LAST

The last() function is used to return the last value of the specified column. Syntax for SQL SELECT LAST() FUNCTION:

You should note that the last() function is only supported in MS Access. But there are ways to get the last record in MySql, SQL Server, Oracle etc. databases.

Select LAST table syntax:

SELECT LAST (column_name) FROM table_name;

select table output:

SQL SELECT RANDOM

The SQL SELECT RANDOM() function returns the random row. It can be used in online exam to display the random questions.

There are a lot of ways to select a random record or row from a database table. Each database server needs different SQL syntax.

Select RANDOM table syntax:

SELECT column FROM table ORDER BY RAND ( ) LIMIT 1

select RANDOM table output:

SQL Tutorial

• what is table ? How do to create in Mysql?


• MySQL drop table


• MySQL RENAME Table


• MySQL TRUNCATE


• MySQL ALTER Table

ALTER TABLE add multiple columns in sql

How do you ALTER TABLE in SQL ?

The SQL ALTER TABLE command is used to add, delete or modify columns in an existing table. You should also use the ALTER TABLE command to add and drop various constraints on an existing table

The ALTER TABLE statement is used to add, delete, or modify columns in an existing table. The ALTER TABLE statement is also used to add and drop various constraints on an existing table.

In many situations, you may require to add the columns in the existing table. Instead of creating a whole table or database again you can easily add single and multiple columns using the ADD keyword.

1 . ADD Column

Syntax of ALTER TABLE ADD Column statement in SQL

ALTER TABLE table_name ADD column_name column-definition;

The above syntax only allows you to add a single column to the existing table. If you want to add more than one column to the table in a single SQL statement, then use the following syntax:

ADD Column in table output:

2 MODIFY Column

The MODIFY keyword is used for changing the column definition of the existing table.

Syntax of ALTER TABLE MODIFY Column

ALTER TABLE table_name MODIFY column_name column-definition;

This syntax only allows you to modify a single column of the existing table. If you want to modify more than one column of the table in a single SQL statement, then use the following syntax:

MODIFY Column in table output:

3 DROP Column

In many situations, you may require to delete the columns from the existing table. Instead of deleting the whole table or database you can use DROP keyword for deleting the columns.

Syntax of ALTER TABLE DROP Column statement in SQL

ALTER TABLE table_name DROP Column column_name ;

DROP Column in table output:

4 RENAME Column

The RENAME keyword is used for changing the name of columns or fields of the existing table.

Syntax of ALTER TABLE RENAME Column

ALTER TABLE table_name RENAME COLUMN old_name to new_name;

RENAME Column in table output:

SQL Tutorial

• what is table ? How do to create in Mysql?


• MySQL drop table


• MySQL RENAME Table


• MySQL TRUNCATE


• MySQL ALTER Table

How do you Rename a table in SQL?

How do you Rename a table in SQL?

In some situations, database administrators and users want to change the name of the table in the SQL database because they want to give a more relevant name to the table.

Any database user can easily change the name by using the RENAME TABLE and ALTER TABLE statement in Structured Query Language.

Here, we have taken the following two different SQL examples, which will help you how to change the name of the SQL table in the database using RENAME statement:

Rename table syntax:

ALTER TABLE old_table_name RENAME TO new_table_name;

Rename table output:

• First, specify the name of the table to be renaming.


• Second, specify the name of the database in which the table was created and the name of the schema to which the table belongs. The database name is optional.


• Third, use IF EXISTS clause to remove the table only if it exists. The IF EXISTS clause has been supported since SQL Server 2016 13.x. If you remove a table that does not exist, you will get an error. The IF EXISTS clause conditionally removes the table if it already exists.

SQL Tutorial

• what is table ? How do to create in Mysql?


• MySQL drop table


• MySQL RENAME Table


• MySQL TRUNCATE


• MySQL ALTER Table

How do you drop a table in SQL?

How do you drop a table in SQL?

The SQL DROP TABLE statement is used to remove a table definition and all the data, indexes, triggers, constraints and permission specifications for that table

The SQL Server (Transact-SQL) DROP TABLE statement allows you to remove or delete a table from the SQL Server database.

This is very important to know that once a table is deleted all the information available in the table is lost forever, so we have to be very careful when using this command.

DROP table syntax:

DROP table tablename ;

DROP table output:

DROP

• First, specify the name of the table to be removed.


• Second, specify the name of the database in which the table was created and the name of the schema to which the table belongs. The database name is optional. If you skip it, the DROP TABLE statement will drop the table in the currently connected database.


• Third, use IF EXISTS clause to remove the table only if it exists. The IF EXISTS clause has been supported since SQL Server 2016 13.x. If you remove a table that does not exist, you will get an error. The IF EXISTS clause conditionally removes the table if it already exists.

Note:

Be careful before dropping a table. Deleting a table will result in loss of complete information stored in the table!

DROP TABLE and CREATE TABLE should not be executed on the same table in the same batch. Otherwise an unexpected error may occur.

It is sometimes easier to drop a table and recreate it, instead of using the ALTER TABLE statement to change the table's definition

Create table in SQL WITH PRIMARY key

What is Table in ,MySql

SQL CREATE TABLE statement is used to create table in a database. If you want to create a table, you should name the table and define its column and each column's data type.

Tables are used to store data in the database. Tables are uniquely named within a database and schema. Each table contains one or more columns. And each column has an associated data type that defines the kind of data it can store e.g., numbers, strings, or temporal data.

create table syntax:

Create table tablename ( column1 datatype, column2 datatype, column3 datatype, column4 datatype,)

The data type of the columns may vary from one database to another. For example, NUMBER is supported in Oracle database for integer value whereas INT is supported in MySQL.

Let us take an example to create a STUDENTS table with ID as primary key and NOT NULL are the constraint showing that these fields cannot be NULL while creating records in the table.

create table output:

create

Now you have the STUDENTS table available in your database and you can use to store required information related to students

The column parameters specify the names of the columns of the table. The datatype parameter specifies the type of data the column can hold (e.g. varchar, integer, date, etc.).

Note:

In addition to the standard reserved keywords, the following keywords cannot be used as column identifiers because they are reserved for ANSI-standard context functions CURRENT_DATE CURRENT_ROLE, CURRENT_TIME, CURRENT_TIMESTAMP, CURRENT_USER

DEFAULT and AUTOINCREMENT are mutually exclusive; only one can be specified for a column.

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Write a program to implement stack using stack class in data structure

Write a program to implement stack using stack class in data structure

Introduction Stack

Stack is a linear data structure which follows a particular order in which the operations are performed. The order may be LIFO(Last In First Out) or FILO(First In Last Out).

There are many real-life examples of a stack. Consider an example of plates stacked over one another in the canteen. The plate which is at the top is the first one to be removed, i.e. the plate which has been placed at the bottommost position remains in the stack for the longest period of time. So, it can be simply seen to follow LIFO(Last In First Out)/FILO(First In Last Out) order.

stack

stack operations Algorithm by using Array

1. PUSH:-When we insert an element in a stack then the operation is known as a push. If the stack is full then the overflow condition occurs.

2. POP:- When we delete an element from the stack, the operation is known as a pop. If the stack is empty means that no element exists in the stack, this state is known as an underflow state.

3.isEmpty:- It determines whether the stack is empty or not.

4. peek:- It returns the element at the given position.

stack implementation by using Array

  import java.util.Stack;;

  class stackclass {

  public static void main(String[] args)   {

     Stack< String > animals = new Stack < >();

     animals.push("shubhi");

     animals.push("narayan");

      animals.push("mane");

     System.out.println(animals);

     animals.pop();

     System.out.println(animals);

       }

    }

output

[shubhi, narayan, mane]
[shubhi, narayan]

stack implementations ways

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• how implement stack By using stack class

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Write a program to implement stack using array in data structure

Write a program to implement stack using array in data structure

Introduction Stack

Stack is a linear data structure which follows a particular order in which the operations are performed. The order may be LIFO(Last In First Out) or FILO(First In Last Out).

There are many real-life examples of a stack. Consider an example of plates stacked over one another in the canteen. The plate which is at the top is the first one to be removed, i.e. the plate which has been placed at the bottommost position remains in the stack for the longest period of time. So, it can be simply seen to follow LIFO(Last In First Out)/FILO(First In Last Out) order.

stack

stack operations Algorithm by using Array

1. PUSH:-When we insert an element in a stack then the operation is known as a push. If the stack is full then the overflow condition occurs.

   top=top+1;

   arr[top]=i

2. POP:- When we delete an element from the stack, the operation is known as a pop. If the stack is empty means that no element exists in the stack, this state is known as an underflow state.

   top=top-1;

3.isEmpty:- It determines whether the stack is empty or not.

top=-1
 

4. peek:- It returns the element at the given position.

stack implementation by using Array

  import java.util.Scanner;

  class stack  {

      int n=10;

      int top=-1;

      int a[] =new int[10];

      Scanner sc = new Scanner(System.in);

    void push()

      {

        if(top== (n-1))

          {

            System.out.println("stcak is overflow");

            }

      else

        {

          System.out.println("enter the number");

          int i =sc.nextInt();

          top=top+1;

          a[top]=i;

          System.out.println("item inseret"

      }

    }

    void pop()

    {

      if(top== -1)

      {

          System.out.println("stcak is underflow");

      }

    else

      {

          top=top-1;

          System.out.println("item delete"

      }

    }

    void display()

       {

        for(int j=top; j>=0 ;j--)

        {

          System.out.println(a[j]

          }

        }

    }

  class stack_array {

  public static void main(String[] args)   {

    {

      Scanner sc = new Scanner(System.in);

      stack s = new stack();

      while(true)

      {

          System.out.println("\n \n \n \n")

          System.out.println("\t \t 1 push")

          System.out.println("\t \t 2 pop")

          System.out.println("\t \t 3 display ")

          System.out.println("\t \t 4 exit")

        System.out.println("enter the choic"

          int ch =sc.nextInt();

    switch(ch)

      {

        case 1: s.push(); break;

       case 2: s.pop(); break;

        case 3: s.display(); break;

        case 4: System.exit(1); break;

        default: System.out.println("try again"

       }

    }

    }

   }

stack implementations ways

• how implement stack By using array
• how implement stack By using Linked list
• how implement stack By using stack class

Next Topic

• Array
• String
• Stack
• Queue
• Linked Lists
• Tree
• Graph