SQL

EVERYTHING I LEARNED ON SQL

SQL (Structured Query Language) SQL is a database computer language used in retrieving and modifying a data in a relational database management system.

Relational Database Management System (RDBMS) The relational database management system serves as the link between different database tables, the database in an RDBMS is stored in a database object called TABLE

DATABASE TABLE The table is a collection of related database entries, and consist of rows and columns.

the field is a column that stores a particular set of related data the record are stored in row, and they are information about a perticular subject

DATA CONSTRAINT These are rules that are used to limit data entries in a table, it can either be applied to a column or the entire table. code example (SELECT firstname, lastname and address FROM contacts )

types of operators

1. Aritmetic operator (+,-,*,% and /)
2. comparism operator (=,!=,<,>,<>,!<,!>,<=,>=,)
3. logical operator (and, in, between, any, and, all, like, not, unique, is not) logical operator (BETWEEN) code example (SELECT * FROM Table1 ORDER BY age BETWEEN 10 200)

EXPRESSION An expression is a combinatin of one or more value, either an operator or a function that elevates to a value. code example (WHERE) (SELECT * FROM table1 ORDER BY firstname WHERE country = nigeria)

BASIC DATABASE SYNTAX

1. create database ( CREATE DATABASE databaseName) to create
2. DROP database ( DROP DATABASE databaseName) to delete
3. USE database ( USE databaseName) to select from a list of database
4. CREATE TABLE example>>>> CREATE TABLE table_name( column1 datatype, column2 datatype, column3 datatype, ..... columnN datatype, PRIMARY KEY(one or more column));
5. DROP TABLE ()