1. Structured Query Language (SQL)
A Level Only
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2. Structured Query Language
Structured query language (SQL) is the language used to search databases. Here is an example of an SQL statement.
SELECT FirstName FROM Student WHERE Gender = “Male”
Fields to show
The table
Search criteria
This statement selects the FirstName field from the Student table and only shows the male students. Consider this table:
StudentID
FirstName
LastName
Address
Gender 1
John
Curtis
12 Brook Lane
Male 2
Ben
Jackson
1 Totters Lane 3
Sarah
Smith
60 Belsize Rd
Female
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3. Results SELECT FirstName FROM Student WHERE Gender = “Male”
StudentID
FirstName
LastName
Address
Gender 1
John
Curtis
12 Brook Lane
Male 2
Ben
Jackson
1 Totters Lane 3
Sarah
Smith
60 Belsize Rd
Female
SELECT FirstName FROM Student WHERE Gender = “Male”
Fields to show
The table
Search criteria
These are the results of the query.
FirstName
John
Ben
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4. Comparison Operators
The following comparison operators are used in SQL statements:
Comparison operator
Symbol
Equal to =
Less than
<
Greater than
>
Less than or equal to
<=
Greater than or equal to
>=
Not equal to
<>
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5. Combining Conditions SELECT FirstName FROM Student
StudentID
FirstName
LastName
TestScore
Gender 1
John
Curtis 55
Male 2
Ben
Jackson 75 3
Sarah
Smith 80
Female
We can use the AND operator to combine conditions.
SELECT FirstName FROM Student
WHERE Gender = “Male” AND TestScore >= 75
These are the results of the query.
TestScore
Ben
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6. Inserting a Record
A new record can be added to a table using the INSERT command.
INSERT INTO Student
VALUES (4, “Eloise”, “Roberts”, “9 Baynes Mews”, “Female”)
StudentID
FirstName
LastName
Address
Gender 1
John
Curtis
12 Brook Lane
Male 2
Ben
Jackson
1 Totters Lane 3
Sarah
Smith
60 Belsize Rd
Female 4
Eloise
Roberts
9 Baynes Mews
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7. Deleting a Record DELETE FROM Student WHERE StudentID = 3
Records can be deleted from a table using the DELETE command.
DELETE FROM Student WHERE StudentID = 3
StudentID
FirstName
LastName
Address
Gender 1
John
Curtis
12 Brook Lane
Male 2
Ben
Jackson
1 Totters Lane 3
Sarah
Smith
60 Belsize Rd
Female 4
Eloise
Roberts
9 Baynes Mews
StudentID
FirstName
LastName
Address
Gender 1
John
Curtis
12 Brook Lane
Male 2
Ben
Jackson
1 Totters Lane 4
Eloise
Roberts
9 Baynes Mews
Female
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8. Updating a Record UPDATE Student SET Address = “45 Cleveland Rd”
Records can be updated using the UPDATE command.
UPDATE Student
SET Address = “45 Cleveland Rd”
WHERE StudentID = 2
StudentID
FirstName
LastName
Address
Gender 1
John
Curtis
12 Brook Lane
Male 2
Ben
Jackson
1 Totters Lane 4
Eloise
Roberts
9 Baynes Mews
Female
45 Cleveland Rd
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9. Multiple Tables SELECT FirstName, LastName, Title, TeacherName
Data can be retrieved from multiple tables using an SQL statement.
SELECT FirstName, LastName, Title, TeacherName
FROM Student, Teacher
WHERE Student.TeacherID = Teacher.TeacherID
StudentID
FirstName
LastName
TeacherID
001
Alex
Bennett
002
James
Hadwen
003
Eloise
Roberts
004
Patrick
Dua-Brown
TeacherID
Title
TeacherName
001 Mr
Smith
002
Ford
003
Mrs
Patel
004
Miss
Wright
A linking condition is used to join the two tables together.
Dot notation is used to specify which table a field is in.
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10. Sorting Results SELECT FirstName FROM Student WHERE Gender = “Male”
The results of a query can be sorted using the ORDER BY command.
SELECT FirstName FROM Student WHERE Gender = “Male”
ORDER BY LastName
This will order the results by the students’ last names in ascending order.
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11. Creating a Table CREATE TABLE Student (
A new table can be created using the CREATE TABLE command.
CREATE TABLE Student (
StudentID INT PRIMARY KEY NOT NULL
FirstName VARCHAR(20)
LastName VARCHAR(20)
Gender VARCHAR(1) )
NOT NULL means the field can’t be left blank.
VARCHAR is a string with a variable length; the maximum length is the value in the brackets.
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12. END