Day02 Lesson02 SQL Basics
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Transcript of Day02 Lesson02 SQL Basics
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Integer:
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Bit - 1 bit
Tinyint - 1 byte
Smallint - 2 bytes
Int - 4 bytes
Bigint - 8 bytes
Float:
Float
Real
Text:
Non unicode string: A character occupies 1 byte
Char
Varchar
Text
Unicode string: A character occupies 2 bytes
Nchar
Nvarchar
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create table Student
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(
sid int,
sname varchar(20)
)
Drop table student;
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Add new column:
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Alter table test add grade char(1);
Modify a column data type:
Alter table test alter column grade varchar(10);
Delete a column:
Alter table test drop column grade;
A table can have only one clustered index and any number of non clustered
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index (upto 249)
Unique index – When a unique index exists, the Database Engine checks for duplicate values each time data is added by a insert operations. Insert operations that would generate duplicate key values are rolled back, and the Database Engine displays an error message.
Clustered index - clustered index can be rebuilt or reorganized on demand to control table fragmentation. A clustered index can also be created on a view. This improves the performance.
Non clustered index - Creates an index that specifies the logical ordering of a table. With a nonclustered index, the physical order of the data rows is independent of their indexed order.
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insert into Student values(1,'Ramu')
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insert into Student(sid,sname) values(6,'Raj')
insert into Student(sid) values(2)
insert into Student(sname) values('Seetha')
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update student
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set sid=3
This will set sid =3 for all students
update student
set sid=1
where sname='Ramu‘
This will set sid as 1 only for Ramu
update student
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set sid=3
This will set sid =3 for all students
update student
set sid=1
where sname='Ramu‘
This will set sid as 1 only for Ramu
delete from student
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where sid between 1 and 3
This will delete students with sid 1,2,3
To execute a statement in MS SQL, Select the statement and Click on the
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Execute button in the query analyser or press F5
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The TOP clause can be very useful on large tables with thousands of records.
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Returning a large number of records can impact on performance.
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To select distinct rows, we need to use the distinct key word
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Select distinct name from orders;
Orders
--------
Id Name
-- -------
1 Ram
2 Krish
3 Ram
4 Raj
Will fetch
Ram
Krish
Raj
Select count(name) from orders; will yield the result as 4
Related rows can be grouped together by GROUP BY clause by specifying a
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column as a grouping column.
GROUP BY is associated with an aggregate function
Example: For each part supplied get the part number and the total shipment quantity
Example: SELECT PNO, SUM(QTY) FROM SP GROUP BY PNO
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