Ch 7Introduction to Structured Query Language (SQL) — Class 11 Informatics Practices, concept-first.

A database becomes useful only when we can actually create it, fill it with data, and ask it questions.

The heart of this section is a contrast between two ways of reaching data. In an ordinary file system, there is no built-in way to ask for data — a programmer must write a full application program for…

Before any SQL can be written, the software that understands it must be on your machine. MySQL is an open source RDBMS, which means it can be downloaded freely — the official website for this is https…

This section sets up the two ideas that every table definition rests on: data types and constraints. Both follow directly from how a relational database is organised.

A data type indicates the type of data value that an attribute can have — and choosing it is more consequential than it looks, because the data type of an attribute decides which operations can be per…

A data type says what kind of value a column may hold; a constraint goes further and restricts which values are acceptable.

Everything in a database begins with structure: before a single row of data exists, someone must declare what tables the database contains and what each column of each table looks like.

A database is a named container managed by the DBMS — tables can only exist inside one. So the first step in building any MySQL project is to create that container, and only after that can relations b…

Creating the database StudentAttendance gives an empty container; the real design work is defining relations (creating tables) inside it.

After a table has been created, you will often need to check exactly how it was defined — which columns it has, their data types, and which constraints apply to them.

A table's structure is rarely perfect on the first attempt. After creating a table you may realise that an attribute needs to be added or removed, that the data type of an existing attribute must chan…

Sometimes a table in a database — or the database itself — needs to be removed altogether. The DROP statement does this: it removes a database or a table permanently from the system.

The CREATE statements of the previous section built the database StudentAttendance with its three relations — STUDENT, GUARDIAN and ATTENDANCE.

A newly created table is an empty frame — the INSERT INTO statement is what puts records into it. Its basic syntax supplies one value per attribute:

Everything so far — creating the database, defining tables, storing and manipulating records — has been preparation for the operation databases really exist for: getting data back out.

Creating tables and filling them with records is only half the story — the real power of a database shows when you start asking it questions.

Every organisation keeps its data in databases organised as related tables. The running example here is a database named OFFICE, which holds several connected tables such as EMPLOYEE and DEPARTMENT.

Data manipulation does not end with putting records into a table and reading them back. Real data changes constantly: an address is corrected, a phone number is replaced, a person leaves and their rec…

Stored data is rarely final. We may need to make changes in the value(s) of one or more columns of existing records — an address changes, a phone number is replaced, a spelling mistake in a name is di…

Records do not stay in a table forever. When an entity leaves the picture — a student leaves the school, an employee resigns — its record has to go.

- A database is a collection of related tables; MySQL is a relational DBMS. A table is a collection of rows and columns, where each row is a record and the columns describe the features (attributes) o…