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Hello and welcome to retrieving data with a SELECT statement.

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In this video, we will learn about retrieving data from

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a relational database table by selecting columns of a table.

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At the end of this lesson,

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you will be able to retrieve data from a relational database table,

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to find the use of a predicate,

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identify the syntax of the SELECT statement using the WHERE clause, and

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list the comparison operators supported by a relational database management system.

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The main purpose of a database management system,

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is not just to store the data but also facilitate retrieval of the data.

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So, after creating a relational database table and inserting data into the table,

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we want to see the data.

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To see the data, we use the SELECT statement.

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The SELECT statement is a data manipulation language statement.

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Data Manipulation Language statements or DML statements are used to read and modify data.

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The SELECT statement is called a query,

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and the output we get from executing this query is called a result set or a result table.

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In its simplest form, a SELECT statement is select star from table name.

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Based on the book entity example,

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we would create the table using

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the entity name book and the entity attributes as the columns of the table.

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The data would be added to the book table by adding

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rows to the table using the insert statement.

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In the book entity example, select star from book gives the result set of four rows.

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All the data rows for all columns in the table book are displayed.

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In addition, you can also retrieve all the rows for all columns by

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specifying the column names individually in the SELECT statement.

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You don't always have to retrieve all the columns in a table.

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You can retrieve just a subset of columns.

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If you want, you can retrieve just two columns from the table book.

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For example book_id and title.

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In this case, the select statement is select book_id, title from book.

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In this case, only the two columns display for each of the four rows.

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Also notice that the order of the columns displayed

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always matches the order in the SELECT statement.

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However, what if we want to know the title of the book whose book_id is B1.

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Relational operation helps us in restricting

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the result set by allowing us to use the clause WHERE.

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The WHERE clause always requires a predicate.

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A predicate is conditioned evaluates to true, false or unknown.

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Predicates are used in the search condition of the WHERE clause.

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So, if we need to know the title of the book whose book_id is B1,

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we use the WHERE clause with the predicate book_id equals B1.

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Select book_id title from book where book_id equals B1.

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Notice the result set is now restricted to

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just one row whose condition evaluates to true.

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The previous example used comparison operator equal to in the WHERE clause.

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There are other comparison operators supported by

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a relational database management system: equal to,

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greater than, less than,

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greater than or equal to,

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less than or equal to, and not equal to.

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Now you can retrieve data and select columns from a relational database table,

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define the use of a predicate,

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identify the syntax of the SELECT statement using the WHERE clause, and

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list the comparison operators supported by a relational database management system.

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Thanks for watching this video.