MySQL-commands.pdf

SQL Commands
 Create a database:
 Open a database:
 Delete a database

Create table Command
 It is used to create a table in a database
 E.g

Insert a Record
 Insert command is used to insert a record
 Insert a row in table
 Insert null values in the table
 Insert values in particular column

Display structure of table
 Describe <table name> or desc <tablename>

Update Command
 It is used to change the record of the table. You can change all the rows or
particular row from the table. The Update command specifies the row with
where clause and new data is written into respective record using set
keyword. E.g
 Student table before change

Various way of Updating records
 Change a particular value
 Updating multiple records
 Updating Null value
 Updating using expression

Delete Records
 There are two commands to delete
records:
 Delete
 Truncate
 Delete:it is used to delete all
rows or particular row from the
table using where clause.
 Truncate: to delete al the row
from table and free the space for
containing the table
 Drop Table: This command is used
to physically delete the table i.e.
remove structure also.
 E.g. of delete
 E.g. of truncate
 E.g. Drop table

Modify the Structure of Table
 Alter Table command is used to modify
the structure of table by modifying the
column definition of its column. It
perform following operations:
 To add new column in table
 To rename column
 To change data type or modify size
 To remove a column physically

Structure after Modification
Before Modification After Modification

SQL Commands
Grouping Records in a Query
•Some time it is required to apply a Select query in a group of
records instead of whole table.
•We can group records by using GROUP BY <column> clause with
Select command. A group column is chosen which have non-
distinct (repeating) values like City, Job etc.
• Generally, the following Aggregate Functions [MIN(), MAX(),
SUM(), AVG(), COUNT()] etc. are applied on groups.
Name Purpose
SUM() Returns the sum of given column.
MIN() Returns the minimum value in the given column.
MAX() Returns the maximum value in the given column.
AVG() Returns the Average value of the given column.
COUNT() Returns the total number of values/ records as per given
column.

SQL Commands
Aggregate Functions & NULL
Consider a table Emp having following records as-
Null values are excluded while (avg)aggregate function is
used
SQL Queries
mysql> Select Sum(Sal) from EMP;
mysql> Select Min(Sal) from EMP;
mysql> Select Max(Sal) from EMP;
mysql> Select Count(Sal) from
EMP; mysql> Select Avg(Sal) from
EMP; mysql> Select Count(*) from
EMP;
Emp
Code Name Sal
E1 Mohak NULL
E2 Anuj 4500
E3 Vijay NULL
E4 Vishal 3500
E5 Anil 4000
Result of query
12000
3500
4500
3
4000
5

SQL Commands
Aggregate Functions & Group
An Aggregate function may applied on a column with DISTINCT or
ALL keyword. If nothing is given ALL is assumed.
Using SUM (<Column>)
This function returns the sum of values in given column orexpression.
mysql> Select Sum(Sal) from EMP;
mysql> Select Sum(DISTINCT Sal) from EMP;
mysql> Select Sum ( S a l ) from EMP where
City=‘Jaipur ’;
mysql> Select Sum ( S a l ) from EMP Group By C i t y ;
mysql> Select Job, Sum(Sal) from EMP Group By Job;
Using MIN (<column>)
This functions returns the Minimum value in the given column.
mysql> Select Min(Sal) from EMP;
mysql> Select Min(Sal) from EMP Group By C i t y ;
mysql> Select Job, Min(Sal) from EMP Group By Job;

SQL Commands
 Using AVG (<column>)
 This functions returns the Average value in the given column.
 Using COUNT (<*|column>)
 This functions returns the number of rows in the given column.
Aggregate Functions & Group
Using MAX (<Column>)
This function returns the Maximum value in given column.
mysql> Select AVG(Sal) from EMP;
mysql> Select AVG(Sal) from EMP Group By C i t
y ;
mysql> Select Max(Sal) from EMP;
mysql> Select Max(Sal) from EMP where City=‘Jaipur ’;
mysql> Select Max(Sal) from EMP Group By C i t y ;
mysql> Select Count ( * ) from EMP;
mysql> Select Count(Sal) from EMP Group By C i t y ;
mysql> Select Count(*), Sum(Sal) from EMP Group By Job;

SQL Commands
Aggregate Functions & Conditions
You may use any condition on group, if required. HAVING
<condition> clause is used to apply a condition on a group.
mysql> Select Job,Sum(Pay) from EMP
Group By Job HAVING Sum(Pay)>=8000;
mysql> Select Job, Sum(Pay) from EMP
Group By Job HAVING Avg(Pay)>=7000;
mysql> Select Job, Sum(Pay) from EMP Group By Job HAVING
Count(*)>=5;
mysql> Select Job, Min(Pay),Max(Pay), Avg(Pay) from EMP Group
By Job HAVING Sum(Pay)>=8000;
mysql> Select Job, Sum(Pay) from EMP Where City=‘Jaipur’
Note :- Where clause works in respect of whole table but Having works on
Group only. If Where and Having both are used then Where will be
executed first.

SQL Commands
Ordering Query Result – ORDER BY Clause
A query result can be orders in ascending (A-Z) or
descending (Z-A)
order as per any column. Default is Ascending order.
mysql> SELECT * FROM Student ORDER BY City;
To get descending order use DESC key word.
mysql> SELECT * FROM Student ORDER BY City
DESC;
mysql> SELECT Name, Fname, City FROM Student
Where Name LIKE ‘R%’ ORDER BY Class;

MySQL-commands.pdf

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