What is a database command?

A database command specifies which particular action you want to perform to the database. The commands are in the form of SQL (Structured Query Language). There are four basic SQL statements that can be passed to the database.

SQL SELECT Statement

This query is used to select certain columns of certain records from a database table.

SELECT * from emp

selects all the fields of all the records from the table name ‘emp’

SELECT empno, ename from emp

selects the fields empno and ename of all records from the table name ‘emp’

SELECT * from emp where empno < 100

selects all those records from the table name ‘emp’ that have the value of the field empno less than 100

SELECT * from article, author where article.authorId = author.authorId

selects all those records from the table name ‘article’ and ‘author’ that have same value of the field authorId

SQL INSERT Statement

This query is used to insert a record to a database table.

INSERT INTO emp(empno, ename) values(101, ‘John Guttag’)

inserts a record to emp table and set its empno field to 101 and its ename field to ‘John Guttag’

SQL UPDATE Statement

This query is used to edit an already existing record in a database table.

UPDATE emp SET ename =‘Eric Gamma’ WHERE empno = 101

updates the record whose empno field is 101 by setting its ename field to ‘Eric Gamma’

SQL DELETE Statement

This query is used to delete the existing record(s) from the database table

DELETE FROM emp WHERE empno = 101

deletes the record whose empno field is 101 from the emp table

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