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Selecting rows

From: MySQL Essential Training

Video: Selecting rows

The Select statement is used for most data retrieval in SQL. The select statement is used for queries that I still have the semi-colon there and you see The astrix is a special token that means SQL does not guarantee that data is returned And I can specify that that's different than the name of You can also use functions in your select queries for example, instead of all You can specify an offset for the starting point with

Selecting rows

The Select statement is used for most data retrieval in SQL. Here, I have the SID application open in my browser and I'm going to choose the world database and, I'm going to enter a simple Select statement, select and a single quote Hello, World and a closing single quote and a semicolon and I'll press the go button here and you see the result is Hello, World. The select statement is used for queries that will return a value or a set of values.

And select is used to display the result of any query. In this case, the query is a literal string with the words Hello, World in it. But it's still a query. It just doesn't come from the database. You could just as easily say select 1 plus 2. I still have the semi-colon there and you see that the query is 1.2 and the result is 3. So now let's get some rows from a table in the database. If I say select asterisk from and the table name is country, like that, semi-colon and we get all the rows from the country table.

You notice the status display says 239 rows returned and it took 13.5 milliseconds to do that. The astrix is a special token that means return all the available columns for this query and the from clause designates the source of the query, in this case a table named country. So this query returned 239 rows, all the rows from the country table. And you'll notice that it's in no particular order. We haven't specified an order, so it may or may not even be in the same order on your system as it is on mine.

SQL does not guarantee that data is returned in any particular order unless you specify an order. You can specify the order with the order by clause and so out here before the semi colon I'm going to type order by and we'll order it by the name column here. So that's this column here and if I press go, you'll see that now they are in alphabetical order by the name of the country. You can also specify which columns you want in your result by listing column names instead of the asterisks.

So if I come over here and select my asterisk, I can say I want the name column, and the life expectancy column, and if I press go you see, now I just get those 2 columns, the name and life expectancy. You can even specify an alternate name for each column in your result set. You notice that here, my result set has this heading which is the name in the result set. And I can specify that that's different than the name of the column by saying as Life Expectancy with a space in it.

And you notice that I have these same single quotes for the literal string, and when I say Go now my column heading which is actually the column name as returned in the results, and that now has Life Expectancy with a space in it. You can also use functions in your select queries for example, instead of all of this, I can say count, parentheses, asterisk, close parentheses. So now it says select, count, from country, order by, name, and inside the parentheses is the parameter to the function.

And this case the only parameter just has the one parameter which is an asterisk which means to count all the rows. And so when I say Go, you see it now has a count of 239 rows. So the count function returns the number of rows in the country table. Now again, if I just bring back our asterisk, so this is going to be all the columns, and if I say Go here you see we get 239 rows, like we did at first. Now, I can limit the number of rows in my result by using the limit clause.

And say LIMIT 5, and now we just get 5 rows returned, you see it says 5 rows up there in the status line, and we have 5 rows here in our results. You can specify an offset for the starting point with an offset clause, so if I say LIMIT 5 OFFSET 5. It'll start those 5, 5 in. So, I'll get whatever's after Andorra, which is Angola and I'll get the next 5. And this is really useful for paging applications, and you'll want to notice that the offset clause must be after the limit clause.

If I put these in the other order, that will not work. The select statement is how you get a result from an SQL query. It's fundamental in SQL and you'll use it for many purposes, here we've been using it to get rows of data from the table. You'll see a lot more examples throughout the rest of the course.

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This video is part of

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MySQL Essential Training

60 video lessons · 6792 viewers

Bill Weinman
Author

 
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  1. 4m 22s
    1. Welcome
      1m 3s
    2. Using the exercise files
      1m 31s
    3. What is MySQL?
      1m 48s
  2. 45m 37s
    1. Installation overview
      3m 16s
    2. Installing XAMPP on Windows
      5m 55s
    3. Installing XAMPP on the Mac
      6m 38s
    4. Setting up MySQL users
      11m 31s
    5. Installing SID on Windows
      5m 43s
    6. Installing SID on the Mac
      6m 6s
    7. Installing time zone support in MySQL on Windows
      6m 28s
  3. 45m 43s
    1. The SELECT statement
      3m 57s
    2. Selecting rows
      4m 57s
    3. Selecting columns
      3m 8s
    4. Sorting results with ORDER BY
      2m 58s
    5. Filtering results with WHERE
      3m 52s
    6. Filtering results with LIKE and IN
      3m 41s
    7. Filtering results with regular expressions
      8m 21s
    8. Inserting rows
      4m 9s
    9. Updating rows
      2m 21s
    10. Deleting rows
      2m 25s
    11. Literal strings
      3m 12s
    12. Understanding NULL
      2m 42s
  4. 41m 47s
    1. Creating a database
      4m 30s
    2. Creating a table
      7m 18s
    3. Creating indexes
      6m 8s
    4. Controlling column behavior with constraints
      4m 46s
    5. Creating an ID column
      6m 58s
    6. Using foreign key constraints
      7m 58s
    7. Altering a table
      4m 9s
  5. 28m 56s
    1. What are data types?
      4m 1s
    2. Numeric types
      5m 21s
    3. String types
      2m 58s
    4. Date and time types
      7m 2s
    5. Bit type
      2m 26s
    6. Boolean values
      2m 15s
    7. Enumeration types
      4m 53s
  6. 32m 34s
    1. String functions
      6m 57s
    2. Numeric functions
      6m 2s
    3. Date and time functions
      4m 12s
    4. Time zones in MySQL
      3m 37s
    5. Formatting dates
      1m 51s
    6. Aggregate functions
      5m 45s
    7. Flow control with CASE
      4m 10s
  7. 7m 6s
    1. Maintaining database integrity with transactions
      4m 46s
    2. Using transactions for performance
      2m 20s
  8. 16m 49s
    1. Updating a table with a trigger
      5m 11s
    2. Preventing automatic updates with a trigger
      7m 29s
    3. Logging transactions with a trigger
      4m 9s
  9. 14m 11s
    1. Creating a simple subselect
      3m 23s
    2. Searching within a result set
      3m 53s
    3. Creating a view
      3m 32s
    4. Creating a joined view
      3m 23s
  10. 12m 26s
    1. Understanding MySQL stored routines
      2m 0s
    2. Creating a stored function
      4m 34s
    3. Creating a stored procedure
      5m 52s
  11. 14m 4s
    1. The multi-platform PDO interface
      3m 44s
    2. Executing the SQL
      4m 8s
    3. Implementing auto-increment IDs
      2m 3s
    4. Using a stored funciton
      4m 9s
  12. 1m 3s
    1. Goodbye
      1m 3s

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