class 4 - SQL COMMANDS and sample code to Create tables with constraints
- List of SQL commands
SQL, 'Structured Query Language',
is a programming language designed to manage data stored in relational
databases. SQL operates through simple, declarative statements. This keeps data
accurate and secure, and helps maintain the integrity of databases, regardless
of size.
Here's an appendix of commonly
used commands.
COMMANDS
ALTER
TABLE
ALTER TABLE table_name ADD column datatype;
ALTER TABLE lets you add
columns to a table in a database.
AND
SELECT column_name(s)
FROM table_name
WHERE column_1 = value_1
AND column_2 = value_2;
AND is an operator
that combines two conditions. Both conditions must be true for the row to be
included in the result set.
AS
SELECT column_name AS 'Alias'
FROM table_name;
AS is a keyword in SQL that allows you to rename a column or
table using an alias.
AVG
SELECT AVG(column_name)
FROM table_name;
AVG() is an aggregate
function that returns the average value for a numeric column.
BETWEEN
SELECT column_name(s)
FROM table_name
WHERE column_name BETWEEN value_1 AND value_2;
The
BETWEEN operator is used
to filter the result set within a certain range. The values can be numbers,
text or dates.
COUNT
SELECT COUNT(column_name)
FROM table_name;
COUNT() is a function that
takes the name of a column as an argument and counts the number of rows where
the column is not NULL.
CREATE
TABLE
CREATE TABLE table_name (column_1 datatype, column_2 datatype, column_3 datatype);
CREATE TABLE creates a new
table in the database. It allows you to specify the name of the table and the
name of each column in the table.
DELETE
DELETE FROM table_name WHERE some_column = some_value;
DELETE statements are
used to remove rows from a table.
GROUP BY
SELECT COUNT(*)
FROM table_name
GROUP BY column_name;
GROUP BY is a clause in SQL
that is only used with aggregate functions. It is used in collaboration with
the SELECT statement to arrange identical data into groups.
INNER
JOIN
SELECT column_name(s) FROM table_1
JOIN table_2
ON table_1.column_name = table_2.column_name;
An
inner join will combine rows from different tables if the join condition is true.
INSERT
INSERT INTO table_name (column_1, column_2, column_3) VALUES (value_1, 'value_2', value_3);
INSERT statements are
used to add a new row to a table.
LIKE
SELECT column_name(s)
FROM table_name
WHERE column_name LIKE pattern;
LIKE is a special
operator used with the WHERE clause to search for a
specific pattern in a column.
LIMIT
SELECT column_name(s)
FROM table_name
LIMIT number;
LIMIT is a clause that
lets you specify the maximum number of rows the result set will have.
MAX
SELECT MAX(column_name)
FROM table_name;
MAX() is a function that
takes the name of a column as an argument and returns the largest value in that
column.
MIN
SELECT MIN(column_name)
FROM table_name;
MIN() is a function that
takes the name of a column as an argument and returns the smallest value in
that column.
OR
SELECT column_name
FROM table_name
WHERE column_name = value_1
OR column_name = value_2;
OR is an operator
that filters the result set to only include rows where either condition is true.
ORDER BY
SELECT column_name
FROM table_name
ORDER BY column_name ASC|DESC;
ORDER BY is a clause that
indicates you want to sort the result set by a particular column either
alphabetically or numerically.
OUTER
JOIN
SELECT column_name(s) FROM table_1
LEFT JOIN table_2
ON table_1.column_name = table_2.column_name;
An
outer join will combine rows from different tables even if the the join
condition is not met. Every row in the left table is
returned in the result set, and if the join condition is not met, then
NULL values are used to
fill in the columns from the right table.
ROUND
SELECT ROUND(column_name, integer)
FROM table_name;
ROUND() is a function that
takes a column name and an integer as an argument. It rounds the values in the
column to the number of decimal places specified by the integer.
SELECT
SELECT column_name FROM table_name;
SELECT statements are
used to fetch data from a database. Every query will begin with SELECT.
SELECT
DISTINCT
SELECT DISTINCT column_name FROM table_name;
SELECT
DISTINCT specifies
that the statement is going to be a query that returns unique values in the
specified column(s).
SUM
SELECT SUM(column_name)
FROM table_name;
C cSUM() is a function that
takes the name of a column as an argument and returns the sum of all the values
in that column.
UPDATE
UPDATE table_name
SET some_column = some_value
WHERE some_column = some_value;
UPDATE statments allow
you to edit rows in a table.
Ex-
update Dummy
set [Order no]=2237,[Item code ]=1176
where [Custmer ID]=151
WHERE
SELECT column_name(s)
FROM table_name
WHERE column_name operator value;
WHERE is a clause that indicates you want to filter the result
set to include only rows where the following condition is
true.
---sample code to create tables
create table student (
regno varchar(5) primary key,
sname varchar(10) not null,
major varchar(10) not null, bdate date not null
);
create table course (
cno int primary key,
cname varchar(10) not null,
dept varchar(10) not null
);
create table enroll (
regno varchar(5),
cno int,
sem int,
marks int not null,
primary key(regno,cno,sem),
foreign key (regno) references student (regno) on delete cascade,
foreign key (cno)
references course (cno) on delete cascade
);
create table text_book (
isbn int primary key,
title varchar(15) not null,
publisher varchar(10) not null,
author varchar(10) not null
);
create table bad (
cno int, sem int,
isbn int not null,
primary key(cno,sem),
foreign key (cno) references course (cno) on delete cascade,
foreign key (isbn) references text_book (isbn) on delete cascade
);
insert into student values ('cs42','nikil','cse','1986-12-17');
insert into student values ('cs48','mujeeb','cse','1986-09-02');
insert into student values ('ec26','pradeep','ece','1987-08-16');
insert into student values ('ec37','majid','ece','1986-05-28');
insert into student values ('is48','vajeed','ise','1986-05-28');
insert into course values (1,'net','computer');
insert into course values (2,'jee','computer');
insert into course values (3,'mis','infosci');
insert into course values (4,'fs','infosci');
insert into course values (5,'oracle','computer');
insert into enroll values('cs42',1,6,98);
insert into enroll values('cs48',2,6,97);
insert into enroll values('ec26',5,5,50);
insert into enroll values('is48',3,7,90);
insert into enroll values('ec37',4,4,80);
insert into enroll values('cs48',1,6,35);
insert into text_book values(101,'let us c','lpe','abc');
insert into text_book values(102,'c++','def','askh');
insert into text_book values(103,'oracle','lmn','qwer');
insert into text_book values(104,'net','lpe','qare');
insert into text_book values(105,'jee','person','hjkn');
insert into bad values (1,6,101);
insert into bad values (2,6,103);
insert into bad values (3,5,102);
insert into bad values (4,4,104);
insert into bad values (5,7,105);
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