
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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