SQL Query

• SQL stands for structured query language.
• Query may retrieve data from database.
• SQL Queries are select, insert, update, delete etc.
  

  Select Statement:

• Select statement is used to retrieve data from one or more tables.
• If you want to select all columns available in the table, use following syntax.
• Syntax: select * from <table name>;
• If you want to select particular columns available in the table, use following syntax.
• Syntax:
• select [column-list]

  from <table name>;

• The Select statement has many clauses.
• Syntax of Select statement:
• select [column-list]

  from <table name>

  [where clause]

  [group by clause]

  [having clause]

  [order by clause];

• Here, column-list includes one or more columns. The clauses are optional.
• Where: Where specifies which rows to retrieve.
• Order by: It is used to sort the data in ascending or descending order.
• Database Table : student_name
  

  Id	firstname	lastname	mname
  1	Juhi	Patel	J
  2	Khyati	Patel	A
  3	Karan	Shah	P
  4	Rohit	Shah	M
  5	Anil	Patel	R
  6	Smita	Patel	A
  7	Komal	Patel	A
  8	Anil	Patel	R
  9	Smita	Patel	J
  10	Khusi	Joshi	H

• Examples:
• 1) Retrieve all rows and columns.
• select * from student_name;

  2) Retrieve lastname from table.

  select lastname from  student_name;

  3) Retrieve firstname  with Id 2 from table.

  select firstname from  student_name  where Id=2;

  4) Retrieve firstname from table sorted by Id  column.

  select firstname from  student_name     order by Id;

  5) Retrieve firstname, lastname from table sorted descending by Id column.

  select firstname from  student_name order by Id desc;

• Distinct: It is used to eliminate duplicate values. It is only use with select statement.
• Syntax: select distinct [column-list]  from <tablename>;
• Examples:
• 1) Remove duplicate values from above table student_name.select distinct * from student_name;

  2) For column firstname remove duplicate values from above table student_name.

  select distinct firstname from student_name;

  3) For column lastname,mname remove duplicate values from above table student_name.

  select distinct lastname, mname from student_name;

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