LibreOffice-Suite-Base/C3/Create-simple-queries-in-SQL-View-II/English-timed
From Script | Spoken-Tutorial
| Visual Cues | Narration |
|---|---|
| 00:02 | Welcome to the Spoken tutorial on LibreOffice Base. |
| 00:06 | In this tutorial, we will learn how to |
| 00:10 | Write Queries in SQL View |
| 00:13 | Use ORDER BY clause |
| 00:15 | Use JOINS |
| 00:17 | Use Aggregate functions |
| 00:19 | Use the GROUP BY clause |
| 00:21 | And to use built in Functions |
| 00:26 | Let us learn more about writing SQL queries |
| 00:31 | For this, let us open our familiar Library database. |
| 00:36 | Now, let us click on the Queries list on the left panel |
| 00:42 | and then click on ‘Create Query in SQL View’. |
| 00:49 | First let us see how we can sort the results of a query. |
| 00:55 | And let us consider the following example: |
| 00:59 | Retrieve Book title and author information for all those books published by Cambridge or Oxford |
| 01:09 | and sort them by the publisher in ascending order, followed by book titles in ascending order. |
| 01:19 | And here is the query: |
| 01:22 | SELECT Publisher, Title, Author |
| 01:28 | FROM Books |
| 01:31 | WHERE Publisher IN ( 'Cambridge', 'Oxford') |
| 01:42 | ORDER BY Publisher ASC, Title ASC |
| 01:50 | So notice we have used the ORDER BY clause to specify Sorting on column names. |
| 01:58 | Also notice the comma characters which help to add more columns for sorting. |
| 02:05 | And to specify the ascending or descending order, we can simply type A S C or D E S C next to each column name. |
| 02:19 | Now, let us click on the Run Query icon below the file menu bar. |
| 02:26 | Here are the books, first sorted by Publisher and then by book title. |
| 02;34 | Now, onto our next query. |
| 02:38 | Let us now get a list of book titles, which have not yet been returned by the members, along with the book issue dates. |
| 02:48 | Since titles are in the Books table and the Book Issue date is in the BooksIssued table, |
| 02:55 | we will need to combine these two somehow. |
| 03:00 | So we will use the JOIN keyword, to join these two tables |
| 03:07 | and we will use the common column, BookId, to link these two tables. |
| 03:14 | So the query is: |
| 03:17 | SELECT B.title, I.IssueDate, I.Memberid
FROM Books B JOIN BooksIssued I |
| 03:35 | ON B.bookid = I.BookId
WHERE CheckedIn = FALSE |
| 03:48 | Notice the letters B and I in the FROM clause. |
| 03:55 | These are called Aliases, which can be either descriptive or just single alphabets for better readability. |
| 04:06 | Notice that the BookId column is in both the tables. |
| 04:11 | So we will use aliases to specify or qualify column names to avoid any confusion |
| 04:21 | Okay, now notice that we have joined the two tables using the JOIN keyword in the FROM clause. |
| 04:31 | and we have specified the BookId column for joining by writing:
ON B.bookid = I.BookId |
| 04:46 | So let us run our query now, |
| 04:49 | and we see a list of books and their issue date and notice that the CheckedIn status; not checked in. |
| 04:59 | Okay, also notice that we see only the memberId in the results. Not very useful, is it? |
| 05:08 | So how do we display member names, which are in the members table? |
| 05:15 | Simple; we JOIN the members table to our query as follows: |
| 05:21 | SELECT B.Title, I.IssueDate, I.MemberId, M.Name
FROM Books B |
| 05:37 | JOIN BooksIssued I ON B.BookId = I.BookId
JOIN Members M ON I.MemberId = M.MemberId |
| 05:58 | WHERE CheckedIn = FALSE |
| 06:02 | So notice the second join with the Members table and the MemberId column used for joining. |
| 06:12 | Let us run the query. |
| 06:14 | Here are the member names, along with the books that were issued to them. |
| 06:20 | Next, let us learn about aggregates and grouping. |
| 06:26 | How can we get a count of all the members in the library? |
| 06:31 | Here is a query: |
| 06:34 | SELECT COUNT(*) AS "Total Members"
FROM Members |
| 06:47 | So here notice the COUNT. |
| 06:51 | This is called an aggregate function, as it returns just one value by evaluating a set of records. |
| 07:02 | Also we have added an Alias ‘Total Members’. |
| 07:07 | Now let us run the query. |
| 07:10 | So here, Base has evaluated all the 4 members records and returned the number 4 which is the total count of members. |
| 07:22 | Some more examples of aggregate functions are SUM, MAX and MIN. |
| 07:30 | Now let us learn about grouping information. |
| 07:36 | How do we get a count of books for each publisher? |
| 07:40 | Here is the query: |
| 07:43 | SELECT Publisher, COUNT(*) AS "Number of Books" FROM Books
GROUP BY Publisher ORDER BY Publisher |
| 08:03 | Notice the new GROUP BY clause. |
| 08:06 | So we are selecting the Publisher and the number of books and the GROUP BY clause to group the records for each Publisher. |
| 08:18 | Let us run the query now. |
| 08:21 | Notice the publisher names and the number of books by each publisher beside them. |
| 08:33 | Next, let us learn about using Functions in SQL. |
| 08:38 | Functions are statements that return a single value. |
| 08:43 | For example, CURRENT_DATE returns today’s date. |
| 08:49 | So let us list all the book titles that are due to be returned by the members. |
| 08:56 | And the query is: |
| 08:58 | SELECT B.Title, I.IssueDate, I.ReturnDate |
| 09:08 | FROM Books B JOIN BooksIssued I ON B.bookid = I.BookId |
| 09:21 | WHERE CheckedIn = FALSE and ReturnDate < CURRENT_DATE |
| 09:31 | So, notice the use of the CURRENT_DATE function. |
| 09:36 | We are retrieving books for which the Return Date is past today’s date. |
| 09:43 | Let us run the query |
| 09:45 | And here are the books that are due to be returned. |
| 09:51 | For a list of functions that HSQLdb offers: go to http://hsqldb.org/doc/2.0/guide/builtinfunctions-chapt.html |
| 10:23 | The entire user guide can be accessed by visiting the website; |
| 10:29 | http://www.hsqldb.org/doc/2.0/guide/ |
| 10:48 | Here is an assignment: |
| 10:50 | Write and test your SQL queries for the following: |
| 10:55 | 1. Get a count of all the books in the Library. |
| 10;58 | 2. Get a count of books written by each author. |
| 11:03 | 3. Get a list of member names and their phone numbers, who need to return books today |
| 11:11 | 4. Explain what this query does?
SELECT (price) AS "Total Cost of Cambridge Books" |
| 11:24 | FROM Books
WHERE publisher = 'Cambridge' |
| 11:32 | This brings us to the end of this tutorial on More Queries in SQL View LibreOffice Base |
| 11:40 | To summarize, we learned how to: |
| 11:43 | Create Queries in SQL View |
| 11:47 | Use ORDER BY clause |
| 11:49 | Use JOINS |
| 11:51 | Use Aggregate functions |
| 11:54 | Use the GROUP BY clause |
| 11:57 | And use built in Functions |
| 12:00 | Spoken Tutorial Project is a part of the Talk to a Teacher project, supported by the National Mission on Education through ICT, MHRD, Government of India. This project is co-ordinated by http://spoken-tutorial.org. More information on the same is available at the following link. |
| 12:21 | This script has been contributed by Priya Suresh, DesiCrew Solutions.
And this is Soundharya, DesiCrew Solutions, signing off.
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