sql kho tài liệu training

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LEARN SQL AND PHP INTRODUCTION TO SQL WHAT IS SQL ?! • Structural Query Language is a language to manage and • To manage data inside database • By manage we mean: • • • • • • • Selecting; Deleting; Updating; Adding; Creating on-demand Functions; Views; Procedures WHAT IS DATABASES • A database is a collection of information that is organized so that it can easily be accessed, managed, and updated WHAT IS DATABASES • FOOD • • • • • FISH MEAT VEGETABLES FRUITS … WHAT IS DATABASES RELATIONAL + DATABASES DATA TYPE OF A DATABASE • A database can contain multiple types of data: • VARCHAR(n): characters where n is a number of characters that admin chose; • INT: integers; • BLOB: for binary data fields(like images, files, maps,…); • LONGBLOB: for long binary files; • DATETIME: date and time field as: YYYY-MM-DD HH:mm:ss; • DATE: for dates only as YYYY-MM-DD; • TIME : for time fields; • YEAR, DECIMAL, TIMESTAMP,… CREATE DATABASE • Regrouping multiple tables that hold a connected information into one environment, represent a database • Syntax: to create a database test_db CREATE SCHEMA IF NOT EXISTS `test_db`; USE `test_db` ; CREATE A TABLE • To create a table inside a database, let us assume that we have a table called test_db that contains columns (id and name) where id is primary key: CREATE TABLE IF NOT EXISTS `test_db`.`test_tbl` ( `id` INT NOT NULL, `name` VARCHAR(20) NOT NULL, PRIMARY KEY (`id `)) • NOT NULL represent a mandatory field to be filled by admins or users SELECT QUERY • Select query consist of selecting all or specific rows or columns of a table when a condition is true; • It provide GROUP BY and ORDER BY functionality; • Syntax: DATA QUERY All data SELECT * FROM tbl_name; Specific columns SELECT id, name, address FROM tbl_name; Specific rows SELECT * FROM tbl_name WHERE id_column >10; SELECT QUERY • GROUP BY: • If sometimes, a specific user in a table has multiple rows of data, we can regroup all of his rows into • Syntax: SELECT * FROM tbl_name GROUP BY column_name; • ORDER BY: • To order data by ascending ASC or descending DESC; • So if we want to re-order the table by placing name_column from A to Z we can use the following query: SELECT * FROM tbl_name GROUP BY column_name ORDER BY column_name ASC; SELECT QUERY • LIMIT 1: • If a user has multiple rows in a table and we want to select at most row for him we add LIMIT clause to the query; • Syntax: SELECT * FROM tbl_name WHERE column_name = ‘X’ LIMIT 1; INSERT QUERY • Insert query help us to add more rows into a table; • Syntax: INSERT INTO tbl_name (name, address, phone_number) VALUES (‘X’, ‘DC’, ‘1234567890’); • If the primary key (usually an ID column) of the table is not Auto-Increment, we should add id to the query INSERT INTO tbl_name (id, name, address, phone_number) VALUES (23, ‘X’, ‘DC’, ‘1234567890’); UPDATE QUERY • If we have a table called test_tbl and contain id as primary key, name, and address, and we need to update a row where an id=29 to new values: • Syntax: UPDATE test_tbl SET name=‘new name’, address = ‘new address’ WHERE id =29; FOREIGN KEYS • A foreign key in a table is a primary key of another; • If we have the following table: • Tbl_address id Name Address X DC Y NY Z LA • Tbl_phone Another_id id Phone_number 5436 123456 5453 534535 5478 324227 FOREIGN KEY • So, the id of the first table is a foreign key into the other; • To create a table with a foreign Key: CREATE TABLE IF NOT EXIST tbl_phone ( new_id INT NOT NULL AUTO INCREMENT, phone_number VARCHAR(18) NOT NULL, PRIMARY KEY (new_id), FOREIGN KEY (id) REFERENCES tbl_address); JOINS • To select multiple rows from different tables we use JOIN; • There is various types of JOINS but the most used is INNER JOIN; • Syntax: SELECT tbl_phone.id, tbl_phone.phone_number, tbl_address.name FROM tbl_phone INNER JOIN tbl_address WHERE tbl_phone.id = tbl_phone.id JOINS • The result of the previous query is: id address Phone_number X 123456 Y 534535 Z 324227 FUNCTIONS – AVG • AVG(): to calculate the average of a column when a certain condition is true; • Syntax: SELECT avg(tbl_name.age_column) FROM tbl_name WHERE age_column > 18; FUNCTIONS – COUNT() • TO count number of rows in a table; • Syntax: SELECT COUNT(id) FROM tbl_name; • Or: SELECT COUNT(id) FROM tbl_name WHERE id
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