SQL Commands
o SQL commands are instructions. It is used to communicate with the database. It is also used to perform specific tasks,
functions, and queries of data.
o SQL can perform various tasks like create a table, add data to tables, drop the table, modify the table, set permission
for users.
Types of SQL Commands
There are five types of SQL commands: DDL, DML, DCL, TCL, and DQL.

1. Data Definition Language (DDL)
   o DDL changes the structure of the table like creating a table, deleting a table, altering a table, etc.
   o All the command of DDL are auto-committed that means it permanently save all the changes in the database.
   Here are some commands that come under DDL:

o CREATE
o ALTER
o DROP
o TRUNCATE
a. CREATE It is used to create a new table in the database.
Syntax:

1. CREATE TABLE TABLE_NAME (COLUMN_NAME DATATYPES[,….]);
   Example:
2. CREATE TABLE EMPLOYEE(Name VARCHAR2(20), Email VARCHAR2(100), DOB DATE);
   b. DROP: It is used to delete both the structure and record stored in the table.
   Syntax
3. DROP TABLE ;
   Example
4. DROP TABLE EMPLOYEE;
   c. ALTER: It is used to alter the structure of the database. This change could be either to modify the characteristics of an existing
   attribute or probably to add a new attribute.
   Syntax:
   To add a new column in the table
5. ALTER TABLE table_name ADD column_name COLUMN-definition;
   To modify existing column in the table:
6. ALTER TABLE MODIFY(COLUMN DEFINITION….);
   EXAMPLE
7. ALTER TABLE STU_DETAILS ADD(ADDRESS VARCHAR2(20));
8. ALTER TABLE STU_DETAILS MODIFY (NAME VARCHAR2(20));
   d. TRUNCATE: It is used to delete all the rows from the table and free the space containing the table.

Syntax:

1. TRUNCATE TABLE table_name;
   Example:
2. TRUNCATE TABLE EMPLOYEE;
3. Data Manipulation Language
   o DML commands are used to modify the database. It is responsible for all form of changes in the database.
   o The command of DML is not auto-committed that means it can’t permanently save all the changes in the database.
   They can be rollback.
   Here are some commands that come under DML:
   o INSERT
   o UPDATE
   o DELETE
   a. INSERT: The INSERT statement is a SQL query. It is used to insert data into the row of a table.
   Syntax:
4. INSERT INTO TABLE_NAME
5. (col1, col2, col3,…. col N)
6. VALUES (value1, value2, value3, …. valueN);
   Or
7. INSERT INTO TABLE_NAME
8. VALUES (value1, value2, value3, …. valueN);
   For example:
9. INSERT INTO javatpoint (Author, Subject) VALUES (“Sonoo”, “DBMS”);
   b. UPDATE: This command is used to update or modify the value of a column in the table.
   Syntax:
10. UPDATE table_name SET [column_name1= value1,…column_nameN = valueN] [WHERE CONDITION]

For example:

1. UPDATE students
2. SET User_Name = ‘Sonoo’
3. WHERE Student_Id = ‘3’
   c. DELETE: It is used to remove one or more row from a table.
   Syntax:
4. DELETE FROM table_name [WHERE condition];
   For example:
5. DELETE FROM javatpoint
6. WHERE Author=”Sonoo”;
7. Data Control Language
   DCL commands are used to grant and take back authority from any database user.
   Here are some commands that come under DCL:
   o Grant
   o Revoke
   a. Grant: It is used to give user access privileges to a database.
   Example
8. GRANT SELECT, UPDATE ON MY_TABLE TO SOME_USER, ANOTHER_USER;
   b. Revoke: It is used to take back permissions from the user.
   Example
9. REVOKE SELECT, UPDATE ON MY_TABLE FROM USER1, USER2;
10. Transaction Control Language
    TCL commands can only use with DML commands like INSERT, DELETE and UPDATE only.
    These operations are automatically committed in the database that’s why they cannot be used while creating tables or
    dropping them.

Here are some commands that come under TCL:
o COMMIT
o ROLLBACK
o SAVEPOINT
a. Commit: Commit command is used to save all the transactions to the database.
Syntax:

1. COMMIT;
   Example:
2. DELETE FROM CUSTOMERS
3. WHERE AGE = 25;
4. COMMIT;
   b. Rollback: Rollback command is used to undo transactions that have not already been saved to the database.
   Syntax:
5. ROLLBACK;
   Example:
6. DELETE FROM CUSTOMERS
7. WHERE AGE = 25;
8. ROLLBACK;
   c. SAVEPOINT: It is used to roll the transaction back to a certain point without rolling back the entire transaction.
   Syntax:
9. SAVEPOINT SAVEPOINT_NAME;
10. Data Query Language
    DQL is used to fetch the data from the database.
    It uses only one command:
    o SELECT

a. SELECT: This is the same as the projection operation of relational algebra. It is used to select the attribute based on the
condition described by WHERE clause.
Syntax:

1. SELECT expressions
2. FROM TABLES
3. WHERE conditions;
   For example:
4. SELECT emp_name
5. FROM employee
6. WHERE age > 20;

• CREATE TABLE
  The SQL CREATE TABLE statement is used to create a new table.
  Syntax
  The basic syntax of the CREATE TABLE statement is as follows –
  CREATE TABLE table_name(
  column1 datatype,
  column2 datatype,
  column3 datatype,
  …..
  columnN datatype,
  PRIMARY KEY( one or more columns )
  );
  CREATE TABLE Employees_details(
  ID int,
  Name varchar(20),
  Address varchar(20)
  );
  Ex:
  CREATE TABLE CUSTOMERS(
  ID INT NOT NULL,
  NAME VARCHAR (20) NOT NULL,
  AGE INT NOT NULL,
  ADDRESS CHAR (25) ,
  SALARY DECIMAL (18, 2),
  PRIMARY KEY (ID)
  );
• DROP TABLE

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.
NOTE − You should be very careful while using this command because once a table is deleted then all the information available
in that table will also be lost forever.
Syntax
The basic syntax of this DROP TABLE statement is as follows −
DROP TABLE table_name;

• INSERT INTO
  The SQL INSERT INTO Statement is used to add new rows of data to a table in the database.
  Syntax
  There are two basic syntaxes of the INSERT INTO statement which are shown below.
  INSERT INTO TABLE_NAME (column1, column2, column3,…columnN)
  VALUES (value1, value2, value3,…valueN);
  Here, column1, column2, column3,…columnN are the names of the columns in the table into which you want to insert the data.
  You may not need to specify the column(s) name in the SQL query if you are adding values for all the columns of the table. But
  make sure the order of the values is in the same order as the columns in the table.
  The SQL INSERT INTO syntax will be as follows −
  INSERT INTO TABLE_NAME VALUES (value1,value2,value3,…valueN);
  Example
  The following statements would create six records in the CUSTOMERS table.
  INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
  VALUES (1, ‘Ramesh’, 32, ‘Ahmedabad’, 2000.00 );
  INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
  VALUES (2, ‘Khilan’, 25, ‘Delhi’, 1500.00 );
  INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
  VALUES (3, ‘kaushik’, 23, ‘Kota’, 2000.00 );
  INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
  VALUES (4, ‘Chaitali’, 25, ‘Mumbai’, 6500.00 );
  INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
  VALUES (5, ‘Hardik’, 27, ‘Bhopal’, 8500.00 );
  INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
  VALUES (6, ‘Komal’, 22, ‘MP’, 4500.00 );
  You can create a record in the CUSTOMERS table by using the second syntax as shown below.
  INSERT INTO CUSTOMERS
  VALUES (7, ‘Muffy’, 24, ‘Indore’, 10000.00 );

All the above statements would produce the following records in the CUSTOMERS table as shown below.
+—-+———-+—–+———–+———-+
| ID | NAME | AGE | ADDRESS | SALARY |
+—-+———-+—–+———–+———-+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+—-+———-+—–+———–+———-+

• The Select Query
  The SQL SELECT statement is used to fetch the data from a database table which returns this data in the form of a result table.
  These result tables are called result-sets.
  Syntax:
  The basic syntax of the SELECT statement is as follows −
  SELECT column1, column2, columnN FROM table_name;
  Here, column1, column2… are the fields of a table whose values you want to fetch. If you want to fetch all the fields available
  in the field, then you can use the following syntax.
  SELECT * FROM table_name;
  Example:
  Consider the CUSTOMERS table having the following records −
  +—-+———-+—–+———–+———-+
  | ID | NAME | AGE | ADDRESS | SALARY |
  +—-+———-+—–+———–+———-+
  | 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
  | 2 | Khilan | 25 | Delhi | 1500.00 |
  | 3 | kaushik | 23 | Kota | 2000.00 |
  | 4 | Chaitali | 25 | Mumbai | 6500.00 |
  | 5 | Hardik | 27 | Bhopal | 8500.00 |
  | 6 | Komal | 22 | MP | 4500.00 |
  | 7 | Muffy | 24 | Indore | 10000.00 |
  +—-+———-+—–+———–+———-+
  The following code is an example, which would fetch the ID, Name and Salary fields of the customers available in CUSTOMERS
  table.
  SQL> SELECT ID, NAME, SALARY FROM CUSTOMERS;
  This would produce the following result −
  +—-+———-+———-+
  | ID | NAME | SALARY |
  +—-+———-+———-+
  | 1 | Ramesh | 2000.00 |
  | 2 | Khilan | 1500.00 |

| 3 | kaushik | 2000.00 |
| 4 | Chaitali | 6500.00 |
| 5 | Hardik | 8500.00 |
| 6 | Komal | 4500.00 |
| 7 | Muffy | 10000.00 |
+—-+———-+———-+
If you want to fetch all the fields of the CUSTOMERS table, then you should use the following query.
SQL> SELECT * FROM CUSTOMERS;
This would produce the result as shown below.
+—-+———-+—–+———–+———-+
| ID | NAME | AGE | ADDRESS | SALARY |
+—-+———-+—–+———–+———-+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+—-+———-+—–+———–+———-+

• WHERE Clause
  The SQL WHERE clause is used to specify a condition while fetching the data from a single table or by joining with multiple
  tables. If the given condition is satisfied, then only it returns a specific value from the table. You should use the WHERE clause
  to filter the records and fetching only the necessary records.
  The WHERE clause is not only used in the SELECT statement, but it is also used in the UPDATE, DELETE statement, etc., which
  we would examine in the subsequent chapters.
  Syntax
  The basic syntax of the SELECT statement with the WHERE clause is as shown below.
  SELECT column1, column2, columnN
  FROM table_name
  WHERE [condition]
  You can specify a condition using the comparison or logical operators like >, <, =, LIKE, NOT, etc. The following examples would
  make this concept clear.
  Example
  Consider the CUSTOMERS table having the following records −
  +—-+———-+—–+———–+———-+
  | ID | NAME | AGE | ADDRESS | SALARY |
  +—-+———-+—–+———–+———-+
  | 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
  | 2 | Khilan | 25 | Delhi | 1500.00 |
  | 3 | kaushik | 23 | Kota | 2000.00 |
  | 4 | Chaitali | 25 | Mumbai | 6500.00 |
  | 5 | Hardik | 27 | Bhopal | 8500.00 |
  | 6 | Komal | 22 | MP | 4500.00 |
  | 7 | Muffy | 24 | Indore | 10000.00 |

• Group By Clause
  The SQL GROUP BY clause is used in collaboration with the SELECT statement to arrange identical data into groups. This GROUP
  BY clause follows the WHERE clause in a SELECT statement and precedes the ORDER BY clause.
  Syntax
  The basic syntax of a GROUP BY clause is shown in the following code block. The GROUP BY clause must follow the conditions
  in the WHERE clause and must precede the ORDER BY clause if one is used.
  SELECT column1, column2
  FROM table_name
  WHERE [ conditions ]
  GROUP BY column1, column2
  ORDER BY column1, column2
  Example
  Consider the CUSTOMERS table is having the following records −
  +—-+———-+—–+———–+———-+
  | ID | NAME | AGE | ADDRESS | SALARY |
  +—-+———-+—–+———–+———-+
  | 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
  | 2 | Khilan | 25 | Delhi | 1500.00 |
  | 3 | kaushik | 23 | Kota | 2000.00 |
  | 4 | Chaitali | 25 | Mumbai | 6500.00 |
  | 5 | Hardik | 27 | Bhopal | 8500.00 |
  | 6 | Komal | 22 | MP | 4500.00 |
  | 7 | Muffy | 24 | Indore | 10000.00 |
  +—-+———-+—–+———–+———-+
  If you want to know the total amount of the salary on each customer, then the GROUP BY query would be as follows.
  SQL> SELECT NAME, SUM(SALARY) FROM CUSTOMERS
  GROUP BY NAME;
  This would produce the following result −
  +———-+————-+
  | NAME | SUM(SALARY) |
  +———-+————-+
  | Chaitali | 6500.00 |
  | Hardik | 8500.00 |
  | kaushik | 2000.00 |
  | Khilan | 1500.00 |
  | Komal | 4500.00 |
  | Muffy | 10000.00 |
  | Ramesh | 2000.00 |
  +———-+————-+
  Now, let us look at a table where the CUSTOMERS table has the following records with duplicate names −
  +—-+———-+—–+———–+———-+
  | ID | NAME | AGE | ADDRESS | SALARY |
  +—-+———-+—–+———–+———-+

| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Ramesh | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | kaushik | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+—-+———-+—–+———–+———-+
Now again, if you want to know the total amount of salary on each customer, then the GROUP BY query would be as follows −
SQL> SELECT NAME, SUM(SALARY) FROM CUSTOMERS
GROUP BY NAME;
This would produce the following result −
+———+————-+
| NAME | SUM(SALARY) |
+———+————-+
| Hardik | 8500.00 |
| kaushik | 8500.00 |
| Komal | 4500.00 |
| Muffy | 10000.00 |
| Ramesh | 3500.00 |
+———+————-+

• Distinct Keyword
  The SQL DISTINCT keyword is used in conjunction with the SELECT statement to eliminate all the duplicate records and fetching
  only unique records.
  There may be a situation when you have multiple duplicate records in a table. While fetching such records, it makes more sense
  to fetch only those unique records instead of fetching duplicate records.
  Syntax
  The basic syntax of DISTINCT keyword to eliminate the duplicate records is as follows −
  SELECT DISTINCT column1, column2,…..columnN
  FROM table_name
  WHERE [condition]
  Example
  Consider the CUSTOMERS table having the following records −
  +—-+———-+—–+———–+———-+
  | ID | NAME | AGE | ADDRESS | SALARY |
  +—-+———-+—–+———–+———-+
  | 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
  | 2 | Khilan | 25 | Delhi | 1500.00 |
  | 3 | kaushik | 23 | Kota | 2000.00 |
  | 4 | Chaitali | 25 | Mumbai | 6500.00 |
  | 5 | Hardik | 27 | Bhopal | 8500.00 |
  | 6 | Komal | 22 | MP | 4500.00 |
  | 7 | Muffy | 24 | Indore | 10000.00 |
  +—-+———-+—–+———–+———-+

First, let us see how the following SELECT query returns the duplicate salary records.
SQL> SELECT SALARY FROM CUSTOMERS
ORDER BY SALARY;
This would produce the following result, where the salary (2000) is coming twice which is a duplicate record from the original
table.
+———-+
| SALARY |
+———-+
| 1500.00 |
| 2000.00 |
| 2000.00 |
| 4500.00 |
| 6500.00 |
| 8500.00 |
| 10000.00 |
+———-+
Now, let us use the DISTINCT keyword with the above SELECT query and then see the result.
SQL> SELECT DISTINCT SALARY FROM CUSTOMERS
ORDER BY SALARY;
This would produce the following result where we do not have any duplicate entry.
+———-+
| SALARY |
+———-+
| 1500.00 |
| 2000.00 |
| 4500.00 |
| 6500.00 |
| 8500.00 |
| 10000.00 |
+———-+

• Alias query
  You can rename a table or a column temporarily by giving another name known as Alias. The use of table aliases is to rename a
  table in a specific SQL statement. The renaming is a temporary change and the actual table name does not change in the
  database. The column aliases are used to rename a table’s columns for the purpose of a particular SQL query.
  Syntax
  The basic syntax of a table alias is as follows.
  SELECT column1, column2….
  FROM table_name AS alias_name
  WHERE [condition];
  The basic syntax of a column alias is as follows.
  SELECT column_name AS alias_name
  FROM table_name
  WHERE [condition];
  Example