SQL Basics

SQL SQL (Structured Query Language) is a special-purpose programming language designed from managing data in relational database management system SQL Instrunctions can be grouped into different classes:  Date defininition language (DDL): create, alter, drop  Data manipulation language (DML):  Insert – insert new data into a database  Update – updates data in a database  Delete – deletes data from a database  Select – extracts data from a database 2

Data definition language (DDL) CREATE TABLE Studenti( nrMatricol int NOT NULL, nume varchar(20) NULL, initialaTatalui varchar(3) NULL, prenume varchar(30) NULL, facultate varchar(10) NULL, specializare varchar(10) NULL, grupa int NULL ) 3

DDL (Cont) CONSTRAINTS NOT NULL - specifies that the column does not accept NULL values PRIMARY KEY - constraints identify the column or set of columns that have values that uniquely identify a row in a table FOREIGN KEY - constraints identify and enforce the relationships between tables. You cannot insert a row with a foreign key value, except NULL, if there is no candidate key with that value.  The ON DELETE clause controls what actions are taken when you try to delete a row to which existing foreign keys point. The ON DELETE clause has the following options: NO ACTION specifies that the deletion fails with an error; CASCADE specifies that all the rows with foreign keys pointing to the deleted row are also deleted; SET NULL specifies that all rows with foreign keys pointing to the deleted row are set to NULL; SET DEFAULT specifies that all rows with foreign keys pointing to the deleted row are set to their default value  The ON UPDATE clause defines the actions that are taken if you try to update a candidate key value to which existing foreign keys point. This clause also supports the NO ACTION, CASCADE, SET NULL and SET DEFAULT options. UNIQUE - constraints enforce the uniqueness of the values in a set of columns CHECK (P), where P is a predicate - constraints enforce domain integrity by limiting the values that can be put in a column 4

DDL (Cont) ALTER TABLE Studenti ADD nationalitate varchar(30) ALTER TABLE Studenti ADD CONSTRAINT PK_nrMatricol primary key (nrMatricol) ALTER TABLE Studenti ALTER COLUMN initialaTatalui varchar(5) 5

DDL (Cont) Drop table table_name Drop view schema_name.view_name Drop function schema_name.function_name Drop index index_name on object_name Drop trigger trigger_name on {database | all server} Drop database database_name Drop schema schema_name Drop role role_name Drop user user_name 6

Data manipulation language (DML) INSERT INTO Studenti (nrMatricol,nume,initialaTatalui,prenume,facultate,specializare,grupa,nationalitate) VALUES (12546,'Georgescu','A','Maria','MI','info-ro',122,'romana') insert into Grupe select grupa, specializare from Studenti 7

DML (Cont) update Studenti set nrMatricol = nrMatricol+1 update Studenti set nume = 'Ionnica' where nrMatricol =

DML (Cont) DELETE FROM Studenti WHERE nrmatricol < DELETE FROM Studenti DELETE * FROM Studenti TRUNCATE TABLE Studenti The difference between truncate and delete removes all rows from a table the operation cannot be rolled back and no triggers will be fired is faster and doesn't use as much undo space as a DELETE. that the truncate resets auto increment column. 9

DML (Cont) SELECT nrMatricol,nume,initialaTatalui,prenume,facultate,specializare,grupa,nationalitate FROM Studenti WHERE nrmatricol = WHERE grupa = 123 WHERE nationalitate is null WHERE prenume like 'V%' WHERE specializare like '%ro' 10

DML (Cont) IS NULL / IS NOT NULL – checks if the column is null or not BETWEEN – selects a range of data between two values. The values can be numbers, text, or dates [val1, val2) EXISTS / NOT EXISTS – returns the value true if the argument subquery is nonempty IN / NOT IN – operator allows you to specify multiple values in a WHERE clause. LIKE / NOT LIKE – operator is used in a WHERE clause to search for a specified pattern in a column; ‘%’ - matches any substring, ‘_’ - matches any character. 11

Aggregate Functions Avg() – returns the average values Min() – returns the min value Max() – returns the max value Sum() – returns the average values Count() – returns the number of rows 12

Stored Procedures CREATE PROC [ EDURE ] [ owner. ] procedure_name [ ; number ] AS sql_statement [...n ] CREATE PROCEDURE au_info_all AS SELECT au_lname, au_fname, title, pub_name FROM authors a INNER JOIN titleauthor ta ON a.au_id = ta.au_id INNER JOIN titles t ON t.title_id = ta.title_id INNER JOIN publishers p ON t.pu EXEC au_info_allb_id = p.pub_id GO 13

Cursor DECLARE cursor_name CURSOR FOR select_statement OPEN cursor_name FETCH NEXT FROM curtor_name WHILE = 0 BEGIN … sql_statement FETCH NEXT FROM curtor_name END CLOSE cursor_name ; DEALLOCATE cursor_name; 14