Components of a table (of a database)
A table is a collection of rows having one or more columns. A row is an instance of a row type. Every row of the same table has the same row type. The value of the n-th field of every row in a table is the value of the n-th column of that row in the table. The row is the smallest unit of data that can be inserted into a table and deleted from a table.
The number of rows in a table is its cardinality. A table whose cardinality is 0 (zero) is said to be empty.
Following image are pictorial presentation of a table and different components of it :
A column name can be used in more than one tables and to maintain the integrity of data and reduce redundancy. This is called a relation.
Elements of a table
The information of a table stored in some heads, those are fields or columns. Columns show vertically in a table.
Each field or column has an individual name. A table cannot contain the same name of two different columns
All the columns in a table make a row. Each row contains all the information of individual topics.
The value of each field makes a row is the column value.
Each table should contain a field which can create a link with another one or more table is the key field of a table.
Practice SQL Exercises
- SQL Exercises, Practice, Solution
- SQL Retrieve data from tables [33 Exercises]
- SQL Boolean and Relational operators [12 Exercises]
- SQL Wildcard and Special operators [22 Exercises]
- SQL Aggregate Functions [25 Exercises]
- SQL Formatting query output [10 Exercises]
- SQL Quering on Multiple Tables [8 Exercises]
- FILTERING and SORTING on HR Database [38 Exercises]
- SQL JOINS
- SQL SUBQUERIES
- SQL Union[9 Exercises]
- SQL View[16 Exercises]
- SQL User Account Management [16 Exercise]
- Movie Database
- BASIC queries on movie Database [10 Exercises]
- SUBQUERIES on movie Database [16 Exercises]
- JOINS on movie Database [24 Exercises]
- Soccer Database
- BASIC queries on soccer Database [29 Exercises]
- SUBQUERIES on soccer Database [33 Exercises]
- Hospital Database
- Employee Database
- More to come!
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SQL: Tips of the Day
What is the simplest SQL Query to find the second largest value?
SELECT MAX(col) FROM table WHERE col NOT IN ( SELECT MAX(col) FROM table );
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