SQL Statements

SQL CREATE Database The SQL CREATE DATABASE statement is used to create new SQL database. Syntax: Basic syntax of CREATE DATABASE statement is as follows: CREATE DATABASE DatabaseName; Always database name should be unique within the RDBMS. Example: If you want to create new database <testDB>, then CREATE DATABASE statement would be as follows: SQL>  CREATE DATABASE   testDB; Make sure you has admin previledge before creating any database. Once a database is created, you can check it in the list of databases as follows: SQL> SHOW DATABASES; +--------------------+ | Database           | +--------------------+ | information_schema | | AMROOD             | | TUTORIALSPOINT     | | mysql              | | orig               | | test               | | testDB             | +--------------------+ 7 rows in set (0.00 sec) DROP or DELETE Database The SQL DROP DATABASE statement is used to drop any existing database in SQL schema. Syntax: Basic syntax of DROP DATABASE statement is as follows: DROP DATABASE DatabaseName; Always database name should be unique within the RDBMS. Example: If you want to delete an existing database <testDB>, then DROP DATABASE statement would be as follows: SQL> DROP DATABASE testDB; NOTE: Be careful before using this operation because by deleting an existing database would  result  in loss of complete information stored in the database. Make sure you has admin previledge before dropping any database. Once a database is dropped, you can check it SQL> in the list of databases as follows:SHOW DATABASES; +--------------------+ | Database           | +--------------------+ | information_schema | | AMROOD             | | TUTORIALSPOINT     | | mysql              | | orig               | | test               | +--------------------+ 6 rows in set (0.00 sec) SQL SELECT Database When you have multiple databases in your SQL Schema, then before starting your  operation, you would need to select a database where all the operations would be performed. The SQL USE statement is used to select any existing database in SQL schema. Syntax: Basic syntax of USE statement is as follows: USE DatabaseName; Always database name should be unique within the RDBMS. Example: You can check available databases as follows: SQL> SHOW DATABASES; +--------------------+ | Database           | +--------------------+ | information_schema | | AMROOD             | | TUTORIALSPOINT     | | mysql              | | orig               | | test               | +--------------------+ 6 rows in set (0.00 sec) Now if you want to work with AMROOD database then you can execute following SQL command and start working with AMROOD database: SQL> USE AMROOD; SQL CREATE Table Creating a basic table involves naming the table and defining its columns and each column's data type. The SQL CREATE TABLE statement is used to create a new table. Syntax: Basic syntax of 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 is the keyword telling the database system what you want to do.in this case, you want to create a new table. The unique name or identifier for the table follows the CREATE TABLE statement. Then in brackets comes the list defining each column in the table and what sort of data type it is.  The syntax becomes clearer with an example below. A copy of an existing table can be created using a combination of the CREATE TABLE statement and the SELECT statement. You can check complete detail at Create Table Using another Tables Create Table Using another Tables A copy of an existing table can be created using a combination of the CREATE TABLE statement and the SELECT statement. The new table has the same column definitions. All columns or specific columns can be selected. When you create a new table using existing table, new table would be populated using existing values in the old table. Syntax: The basic syntax for creating a table from another table is as follows: CREATE  TABLE  NEW_TABLE_NAME  AS  SELECT  [ column1, column2...columnN ]  FROM  EXISTING_TABLE_NAME  [ WHERE ] Here column1, column2...are the fields of existing table and same would be used to create fields of new table. Example: Following  is  an  example  which  would  create  a  table  SALARY  using  CUSTOMERS  table  and  having  fields customer ID, and customer SALARY: SQL> CREATE  TABLE  SALARY  AS  SELECT ID, SALARY  FROM  CUSTOMERS; This would create new table SALARY which would have following records: +----+----------+ | ID | SALARY   | +----+----------+ |  1 |  2000.00 | |  2 |  1500.00 | |  3 |  2000.00 | |  4 |  6500.00 | |  5 |  8500.00 | |  6 |  4500.00 | |  7 | 10000.00 | +----+----------+ Example: Following is an example which creates a CUSTOMERS table with ID as primary key and NOT  NULL are the constraints showing that these fileds can not be NULL while creating records in this table: SQL> 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) ); You can verify if your table has been created successfully by looking at the message displayed by the SQL server otherwise you can use DESC command as follows: SQL> DESC CUSTOMERS; +---------+---------------+------+-----+---------+-------+ | Field   | Type          | Null | Key | Default | Extra | +---------+---------------+------+-----+---------+-------+ | ID      | int(11)       | NO   | PRI |         |       | | NAME    | varchar(20)   | NO   |     |         |       | | AGE     | int(11)       | NO   |     |         |       | | ADDRESS | char(25)       | YES  |     | NULL    |       | | SALARY  | decimal(18,2) | YES   |     | NULL    |       | +---------+---------------+------+-----+---------+-------+ 5 rows in set (0.00 sec) Now you have CUSTOMERS table available in your database which you can use to store required information related to customers. SQL DROP or DELETE Table The SQL DROP TABLE statement is used to remove a table definition and all data, indexes,  triggers, constraints, and permission specifications for that table. NOTE: You have to be careful while using this command because once a table is deleted then all the information available in the table would also be lost forever. Syntax: Basic syntax of DROP TABLE statement is as follows: DROP TABLE table_name; Example: Let us first verify CUSTOMERS table, and then we would delete it from the database: SQL> DESC CUSTOMERS; +---------+---------------+------+-----+---------+-------+ | Field   | Type          | Null | Key | Default | Extra | +---------+---------------+------+-----+---------+-------+ | ID      | int(11)       | NO   | PRI |         |       | | NAME    | varchar(20)   | NO   |     |         |       | | AGE     | int(11)       | NO   |     |         |       | | ADDRESS | char(25)      | YES  |     | NULL    |       | | SALARY  | decimal(18,2) | YES   |     | NULL    |       | +---------+---------------+------+-----+---------+-------+ 5 rows in set (0.00 sec) This means CUSTOMERS table is available in the database, so let us drop it as follows: SQL> DROP TABLE CUSTOMERS; Query OK, 0 rows affected (0.01 sec) Now if you would try DESC command then you would get error as follows: SQL> DESC CUSTOMERS; ERROR 1146 (42S02): Table 'TEST.CUSTOMERS' doesn't exist Here TEST is database name which we are using for our examples. SQL INSERT Query The SQL INSERT INTO Statement is used to add new rows of data to a table in the database. Syntax: There are two basic syntax of INSERT INTO statement is as follows: INSERT  INTO  TABLE_NAME  (column1, column2, column3,...columnN)]  VALUES  (value1, value2, value3,...valueN); Here column1, column2,...columnN are the names of the columns in the table into which you want to insert 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 would be as follows: INSERT INTO TABLE_NAME VALUES (value1,value2,value3,...valueN); Example: Following statements would create six records in 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 CUSTOMERS table using second syntax as follows: INSERT INTO CUSTOMERS  VALUES (7, 'Muffy', 24, 'Indore', 10000.00 ); All the above statement would product following records in CUSTOMERS table: +----+----------+-----+-----------+----------+ | 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 | +----+----------+-----+-----------+----------+ Populate one table using another table: You can populate data into a table through select statement over another table provided another table has a set of fields which are required to populate first table. Here is the syntax: INSERT  INTO  first_table_name  [(column1, column2, ... columnN)] SELECT column1, column2, ...columnN FROM second_table_name [WHERE condition]; SQL SELECT Query SQL SELECT Statement is used to fetch the data from a database table which returns data in the form of result table. These result tables are called result-sets. Syntax: The basic syntax of 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 following syntax: SELECT * FROM table_name; Example: Consider CUSTOMERS table is having 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 | +----+----------+-----+-----------+----------+ Following is an example which would fetch ID, Name and Salary fields of the customers available in CUSTOMERS table: SQL> SELECT ID, NAME, SALARY FROM CUSTOMERS; This would produce 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 CUSTOMERS table then use the following query: SQL> SELECT * FROM CUSTOMERS; This would produce following result: +----+----------+-----+-----------+----------+ | 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 | +----+----------+-----+-----------+----------+ SQL WHERE Clause The SQL WHERE clause is used to specify a condition while fetching the data from single table or joining with multiple table. If the given condition is satisfied then only it returns specific value from the table. You would use WHERE clause to filter the records and fetching only necessary records. The WHERE clause not only used in SELECT statement, but it is also used in UPDATE, DELETE statement etc. which we would examine in subsequent chapters. Syntax: The basic syntax of SELECT statement with WHERE clause is as follows: SELECT column1, column2, columnN FROM table_name WHERE [condition] You can specify a condition using  comparision or logical operators like >, <, =, LIKE, NOT etc. Below examples would make this concept clear. Example: Consider CUSTOMERS table is having 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 | +----+----------+-----+-----------+----------+ Following is an example which would fetch ID, Name and Salary fields from the CUSTOMERS table where salary is greater than 2000: SQL> SELECT ID, NAME, SALARY FROM CUSTOMERS WHERE SALARY > 2000; This would produce following result: +----+----------+----------+ | ID | NAME     | SALARY   | +----+----------+----------+ |  4 | Chaitali |  6500.00 | |  5 | Hardik   |  8500.00 | |  6 | Komal    |  4500.00 | |  7 | Muffy    | 10000.00 | +----+----------+----------+ Following is an example which would fetch ID, Name and Salary fields from the CUSTOMERS table for a customer with name Hardik. Here it is important to note that all the strings should be given inside single quotes ('') where as numeric values should be given without any quote as in above example: SQL> SELECT ID, NAME, SALARY FROM CUSTOMERS WHERE  NAME = 'Hardik'; This would produce following result: +----+----------+----------+ | ID | NAME     | SALARY   | +----+----------+----------+ |  5 | Hardik   |  8500.00 | +----+----------+----------+ SQL AND and OR Operators The  SQL AND and OR operators  are  used  to  combile  multiple  conditions  to  narrow  data  in  an  SQL statement. These two operators are called conjunctive operators. These  operators  provide  a means  to  make  multiple  comparisons  with  different  operators in  the  same  SQL statement. The AND Operator: The AND operator allows the existence of multiple conditions in an SQL statement's WHERE clause. Syntax: The basic syntax of AND operator with WHERE clause is as follows: SELECT column1, column2, columnN FROM table_name WHERE [condition1] AND [condition2]...AND [conditionN]; You can combine N number of conditions using AND operator. For an action to be taken by the SQL statement, whether it be a transaction or query, all conditions separated by the AND must be TRUE. Example: Consider CUSTOMERS table is having 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 | +----+----------+-----+-----------+----------+ Following is an example which would fetch ID, Name and Salary fields from the CUSTOMERS table where salary is greater than 2000 AND age is less tan 25 years: SQL> SELECT ID, NAME, SALARY FROM CUSTOMERS WHERE SALARY > 2000 AND age < 25; This would produce following result: +----+-------+----------+ | ID | NAME  | SALARY   | +----+-------+----------+ |  6 | Komal |  4500.00 | |  7 | Muffy | 10000.00 | +----+-------+----------+ The OR Operator: The OR operator is used to combine multiple conditions in an SQL statement's WHERE clause. Syntax: The basic syntax of OR operator with WHERE clause is as follows: SELECT column1, column2, columnN FROM table_name  WHERE [condition1] OR [condition2]...OR [conditionN] You can combine N number of conditions using OR operator. For an action to be taken by the SQL statement, whether it be a transaction or query, only any ONE of the conditions separated by the OR must be TRUE. Example: Consider CUSTOMERS table is having 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 | +----+----------+-----+-----------+----------+ Following is an example which would fetch ID, Name and Salary fields from the CUSTOMERS table where salary is greater than 2000 OR age is less tan 25 years: SQL> SELECT ID, NAME, SALARY FROM CUSTOMERS WHERE SALARY > 2000 OR age < 25; This would produce following result: +----+----------+----------+ | ID | NAME     | SALARY   | +----+----------+----------+ |  3 | kaushik  |  2000.00 | |  4 | Chaitali |  6500.00 | |  5 | Hardik   |  8500.00 | |  6 | Komal    |  4500.00 | |  7 | Muffy    | 10000.00 | +----+----------+----------+ SQL UPDATE Query The SQL UPDATE Query is used to modify the existing records in a table. You can use WHERE clause with UPDATE query to update selected rows otherwise all the  rows  would be effected. Syntax: The basic syntax of UPDATE query with WHERE clause is as follows: UPDATE  table_name  SET  column1 = value1, column2 = value2...., columnN = valueN  WHERE  [condition]; You can combine N number of conditions using AND or OR operators. Example: Consider CUSTOMERS table is having 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 | +----+----------+-----+-----------+----------+ Following is an example which would update ADDRESS for a customer whose ID is 6: SQL> UPDATE CUSTOMERS SET ADDRESS = 'Pune' WHERE ID = 6; Now CUSTOMERS table would have 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 | Pune      |  4500.00 | |  7 | Muffy    |  24 | Indore    | 10000.00 | +----+----------+-----+-----------+----------+ If you want to modify all ADDRESS and SALARY column values in CUSTOMERS table, you do not need to use WHERE clause and UPDATE query would be as follows: SQL> UPDATE  CUSTOMERS  SET ADDRESS = 'Pune', SALARY = 1000.00; Now CUSTOMERS table would have following records: +----+----------+-----+---------+---------+ | ID | NAME     | AGE | ADDRESS | SALARY   | +----+----------+-----+---------+---------+ |  1 | Ramesh   |  32 | Pune    | 1000.00 | |  2 | Khilan   |  25 | Pune    | 1000.00 | |  3 | kaushik  |  23 | Pune    | 1000.00 | |  4 | Chaitali |  25 | Pune    | 1000.00 | |  5 | Hardik   |  27 | Pune    | 1000.00 | |  6 | Komal    |  22 | Pune    | 1000.00 | |  7 | Muffy    |  24 | Pune    | 1000.00 | +----+----------+-----+---------+---------+ SQL DELETE Query The SQL DELETE Query is used to delete the existing records from a table. You can use WHERE clause with DELETE query to delete selected rows, otherwise all the  records  would be deleted. Syntax: The basic syntax of DELETE query with WHERE clause is as follows: DELETE FROM table_name WHERE [condition]; You can combine N number of conditions using AND or OR operators. Example: Consider CUSTOMERS table is having 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 | +----+----------+-----+-----------+----------+ Following is an example which would DELETE a customer whose ID is 6: SQL> DELETE FROM CUSTOMERS WHERE ID = 6; Now CUSTOMERS table would have 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 | |  7 | Muffy    |  24 | Indore    | 10000.00 | +----+----------+-----+-----------+----------+ If you want to DELETE all the records from CUSTOMERS table, you do not need to use WHERE  clause and DELETE query would be as follows: SQL> DELETE FROM CUSTOMERS; Now CUSTOMERS table would not have any record. SQL LIKE Clause The SQL LIKE clause is used to compare a value to similar values using wildcard operators. There are two wildcards used in conjunction with the LIKE operator:

• The percent sign (%)
• The underscore (_)

The percent sign represents zero, one, or multiple characters. The underscore represents a single  number or character. The symbols can be used in combinations. Syntax: The basic syntax of % and _ is as follows: SELECT FROM  table_name WHERE column LIKE 'XXXX%' or SELECT FROM table_name WHERE column LIKE '%XXXX%' or SELECT FROM table_name WHERE column LIKE 'XXXX_' or SELECT FROM table_name WHERE column LIKE '_XXXX' or SELECT FROM table_name WHERE column LIKE '_XXXX_' You can combine N number of conditions using AND or OR operators. Here XXXX could be any numberic or string value. Example: Here are number of examples showing WHERE part having different LIKE clause with '%' and '_' operators:

Let us take a real example, consider CUSTOMERS table is having 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 | +----+----------+-----+-----------+----------+ Following is an example which would display all the records from CUSTOMERS table where SALARY starts with 200: SQL> SELECT * FROM CUSTOMERS WHERE SALARY LIKE '200%'; This would produce following result: +----+----------+-----+-----------+----------+ | ID | NAME     | AGE | ADDRESS   | SALARY   | +----+----------+-----+-----------+----------+ |  1 | Ramesh   |  32 | Ahmedabad |   2000.00 | |  3 | kaushik  |  23 | Kota      |  2000.00 | +----+----------+-----+-----------+----------+ SQL TOP Clause The SQL TOP clause is used to fetch a TOP N number or X percent records from a table. Note: All the databases do not support TOP clause. For example MySQL supports LIMIT clause to fetch limited number of records and Oracle uses ROWNUM to fetch limited number of records. Syntax: The basic syntax of TOP clause with SELECT statement would be as follows: SELECT TOP number|percent column_name(s) FROM table_name WHERE [condition] Example: Consider CUSTOMERS table is having 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 | +----+----------+-----+-----------+----------+ Following is an example on SQL server which would fetch top 3 records from CUSTOMERS table: SQL> SELECT TOP 3 * FROM CUSTOMERS; This would produce following result: +----+---------+-----+-----------+---------+ | ID | NAME    | AGE | ADDRESS   | SALARY  | +----+---------+-----+-----------+---------+ |  1 | Ramesh  |  32 | Ahmedabad | 2000.00 | |  2 | Khilan  |  25 | Delhi     | 1500.00 | |  3 | kaushik |  23 | Kota      | 2000.00 | +----+---------+-----+-----------+---------+ If you are using MySQL server then, here is equivalent example: SQL> SELECT * FROM CUSTOMERS LIMIT 3; This would produce following result: +----+---------+-----+-----------+---------+ | ID | NAME    | AGE | ADDRESS    | SALARY  | +----+---------+-----+-----------+---------+ |  1 | Ramesh  |  32 | Ahmedabad | 2000.00 | |  2 | Khilan  |  25 | Delhi     | 1500.00 | |  3 | kaushik |  23 | Kota      | 2000.00 | +----+---------+-----+-----------+---------+ If you are using Oracle server then, here is equivalent example: SQL> SELECT * FROM CUSTOMERS WHERE ROWNUM <= 3; This would produce following result: +----+---------+-----+-----------+---------+ | ID | NAME    | AGE | ADDRESS    | SALARY  | +----+---------+-----+-----------+---------+ |  1 | Ramesh  |  32 | Ahmedabad | 2000.00 | |  2 | Khilan  |  25 | Delhi     | 1500.00 | |  3 | kaushik |  23 | Kota      | 2000.00 | +----+---------+-----+-----------+---------+ SQL ORDER BY Clause The  SQL ORDER BY clause is used to sort the data in ascending or descending order, based on one or more columns. Some database sorts query results in ascending order by default. Syntax: The basic syntax of ORDER BY clause is as follows: SELECT column-list FROM table_name [WHERE condition] [ORDER BY column1, column2, .. columnN] [ASC | DESC]; You can use more than one column in the ORDER BY clause. Make sure whatever column you are using to sort, that column should be in column-list. Example: Consider CUSTOMERS table is having 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 | +----+----------+-----+-----------+----------+ Following is an example which would sort the result in ascending order by NAME and SALARY: SQL> SELECT * FROM CUSTOMERS ORDER BY NAME, SALARY; This would produce following result: +----+----------+-----+-----------+----------+ | ID | NAME     | AGE | ADDRESS   | SALARY   | +----+----------+-----+-----------+----------+ |  4 | Chaitali |  25 | Mumbai    |  6500.00 | |  5 | Hardik   |  27 | Bhopal    |  8500.00 | |  3 | kaushik  |  23 | Kota      |  2000.00 | |  2 | Khilan   |  25 | Delhi     |  1500.00 | |  6 | Komal    |  22 | MP        |  4500.00 | |  7 | Muffy    |  24 | Indore    | 10000.00 | |  1 | Ramesh   |  32 | Ahmedabad |   2000.00 | +----+----------+-----+-----------+----------+ Following is an example which would sort the result in descending order by NAME: SQL> SELECT * FROM CUSTOMERS ORDER BY NAME DESC; This would produce following result: +----+----------+-----+-----------+----------+ | ID | NAME     | AGE | ADDRESS   | SALARY   | +----+----------+-----+-----------+----------+ |  1 | Ramesh   |  32 | Ahmedabad |   2000.00 | |  7 | Muffy    |  24 | Indore    | 10000.00 | |  6 | Komal    |  22 | MP        |  4500.00 | |  2 | Khilan   |  25 | Delhi     |  1500.00 | |  3 | kaushik  |  23 | Kota      |  2000.00 | |  5 | Hardik   |  27 | Bhopal    |  8500.00 | |  4 | Chaitali |  25 | Mumbai    |  6500.00 | +----+----------+-----+-----------+----------+ SQL Group By The SQL GROUP BY clause is used in collaboration with the SELECT statement to arrange identical data into groups. The GROUP BY clause follows the WHERE clause in a SELECT statement and precedes the ORDER BY clause. Syntax: The basic syntax of GROUP BY clause is given below. 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 CUSTOMERS table is having 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 salary on each customer, then GROUP BY query would be as follows: SQL> SELECT NAME, SUM(SALARY) FROM CUSTOMERS GROUP BY NAME; This would produce 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 has following table where CUSTOMERS table has 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 GROUP BY query would be as follows: SQL> SELECT NAME, SUM(SALARY) FROM CUSTOMERS GROUP BY NAME; This would produce following result: +---------+-------------+ | NAME    | SUM(SALARY) | +---------+-------------+ | Hardik  |     8500.00 | | kaushik |     8500.00 | | Komal   |     4500.00 | | Muffy   |    10000.00 | | Ramesh  |     3500.00 | +---------+-------------+ SQL Distinct Keyword The SQL DISTINCT keyword is used in conjunction with 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 unique records instead of fetching duplicate records. Syntax: The basic syntax of DISTINCT keyword to eliminate duplicate records is as follows: SELECT DISTINCT column1, column2,.....columnN FROM table_name WHERE [condition] Example: Consider CUSTOMERS table is having 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 duplicate salary records: SQL> SELECT SALARY FROM CUSTOMERS ORDER BY SALARY; This would produce following result where 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 DISTINCT keyword with the above SELECT query and see the result: SQL> SELECT DISTINCT SALARY FROM CUSTOMERS ORDER BY SALARY; This would produce following result where we do not have any duplicate entry: +----------+ | SALARY   | +----------+ |  1500.00 | |  2000.00 | |  4500.00 | |  6500.00 | |  8500.00 | | 10000.00 | +----------+