Click here to load reader

SQL Tutorial

  • View
    991

  • Download
    3

Embed Size (px)

DESCRIPTION

SQL Tutorial

Text of SQL Tutorial

SQL - DatabasesWhat's a Database? A SQL database is nothing more than an empty shell, like a vacant warehouse. It offers no real functionality whatsoever, but does provide a virtual space to store data. Data is stored inside of database objects called tables, and tables are the containers that actually hold specific types of data, such as numbers, files, strings, and dates. A single database can house hundreds of tables containing more than 1,000 table columns each and they may be jam packed with relational data ready to be retrieved by SQL. Perhaps the greatest feature SQL offers is that it doesn't take much effort to rearrange your warehouse to meet your ever-growing business needs.

SQL - Creating a DatabaseCreating a database inside of SQL Express has its advantages. After launching Microsoft's SQL Server Management Studio Express application, simply right-clicking on the Databases folder of the Object Explorer gives you the option to create a New Database. After selecting the New Database... option, name your database "MyDatabase" and press "OK".

Now is the time to press the New Query button located toward the top of the screen, just above the Object Explorer pane.

Pressing this button offers an empty tab. All SQL query statements (code) that we will be exploring will be entered here and executed against the SQL Express database. If you haven't yet created a new database, you may also create a database by typing the following SQL query statement into your new empty query tab, and then pressing the Execute button or striking the (F5) key.

SQL Create Database Query:CREATE DATABASE MyDatabase;

After executing this query, SQL will notify you that your query has run successfully and that the database was created

SQL - TablesData is stored inside SQL tables which are contained within SQL databases. A single database can house hundreds of tables, each playing its own unique role in the database schema. While database architecture and schema are concepts far above the scope of this tutorial, we plan on diving in just past the surface to give you a glimpse of database architecture that begins with a thorough understanding of SQL Tables. Advertise on Tizag.com SQL tables are comprised of table rows and columns. Table columns are responsible for storing many different types of data, like numbers, texts, dates, and even files. There are many different types of table columns and these data types vary, depending on how the SQL table has been created by the SQL developer. A table row is a horizontal record of values that fit into each different table column.

SQL - Create a SQL TableLet's now CREATE a SQL table to help us expand our knowledge of SQL and SQL commands. This new table will serve as a practice table and we will begin to populate this table with some data which we can then manipulate as more SQL Query commands are introduced. The next couple of examples will definitely be overwhelming to novice SQL programmers, but we will take a moment to explain what's going on.

SQL Create Table Query:USE mydatabase; CREATE TABLE orders (id INT IDENTITY(1,1) PRIMARY KEY, customer VARCHAR(50), day_of_order DATETIME, product VARCHAR(50), quantity INT);

The first line of the example, "USE mydatabase;", is pretty straightforward. This line defines the query scope and directs SQL to run the command against the MyDatabase object we created earlier in the SQL Databases lesson. The blank line break after the first command is not required, but it makes our query easier to follow. The line starting with the CREATE clause is

SQL - Queries

SQL coins the term query as the name for its commands. Basically, all SQL code is written in the form query statement and then executed against a database. All SQL queries perform some type of data opera such as selecting data, inserting/updating data, or creating data objects such as SQL databases and SQL tables. Each query statement begins with a clause such as SELECT,UPDATE, CREATE or DELETE. Advertise on Tizag.com

SELECT queries are the most commonly used SQL commands, so let's take a look at a SELECT query will return records from the orders table that we created previously in the SQL Tables lesson.

SQL Query Code:USE mydatabase; SELECT * FROM orders;

SQL Query Results:id customer day_of_order product quantity 1 Tizag 2008-08-01 00:00:00.000 Pen 4 We'll explain the mechanics of this code in the next lesson. For now, just know that SELECT queries essentially tell SQL to go and "fetch" table data for your viewing pleasure.

Here's a look at a few different query types including a INSERT and SELECT query we will be coveri the next lesson, SQL Select.

SQL Query Examples:-- Inserts data into a SQL Database/Table INSERT INTO orders (customer,day_of_order,product, quantity) VALUES('Tizag','8/1/08','Pen',4); -- Selects data from a SQL Database/Table SELECT * FROM orders; -- Updates data in a Database/Table UPDATE orders SET quantity = '6' WHERE id = '1'

SQL - SelectAdvertise on Tizag.com

SQL SELECT may be the most commonly used command by SQL programmers. It is used to extract d from databases and to present data in a user-friendly table called the result set.

SQL Select Query Template:SELECT table_column1, table_column2, table_column3 FROM my_table;

Select queries require two essential parts. The first part is the "WHAT", which determines what we wa SQL to go and fetch. The second part of any SELECT command is the "FROM WHERE". It identifie where to fetch the data from, which may be from a SQL table, a SQL view, or some other SQL data ob

Now we would like SQL to go and fetch some data for us from the orders table that was created in the previous lesson. How do we translate this request into SQL code so that the database application does a work for us? Simple! We just need to tell SQL what we want to select and from where to select the da following the schema outlined below.

SQL Select Query Code:USE mydatabase; SELECT id, customer, day_of_order, product, quantity FROM orders;

SQL Orders Table Results:id customer day_of_order product quantity 1 Tizag 2008-08-01 00:00:00.000 Pen 4 Below, we will manipulate the result output by rearranging the list of table column names inside of the SELECT statement.

SQL Select Query: Rearranged:USE mydatabase;

SQL - Where

The WHERE clause sets a conditional statement, and it can be used with any type of SQL query. As t select query executes, SQL processes one row at a time. Each time the conditional statement is met (returns true), a row is returned as a result. SQL WHERE is essentially, a filtering mechanism for SQL queries and is a tremendous asset to any aspiring SQL developer. Advertise on Tizag.com

SQL Where Query:USE mydatabase; SELECT * FROM orders WHERE customer = 'Tizag'

As we take a look at the results, notice how only the rows that meet the criteria (where the customer co value is Tizag) are returned. In this example, we are using the WHERE clause to filter out rows and on selecting data that meets the conditional statement.

SQL Results:id customer day_of_order product quantity 1 Tizag 2008-08-01 00:00:00.000 Pen 4 2 Tizag 2008-08-01 00:00:00.000 Stapler 1 5 Tizag 2008-07-25 00:00:00.000 19" LCD Screen 3 6 Tizag 2008-07-25 00:00:00.000 HP Printer

SQL - As

SQL AS temporarily assigns a table column a new name. This grants the SQL developer the ability to m adjustments to the presentation of query results and allow the developer to label results more accurately without permanently renaming table columns. Advertise on Tizag.com

SQL Select As Code:USE mydatabase; SELECT day_of_order AS "Date", customer As "Client", product, quantity FROM orders;

SQL Orders Table Results:Date Client product quantity 2008-08-01 00:00:00.000 Tizag Pen 4 SQL AS allows us to use any name at the presentation level and helps the developer better describe a column in the result set.

SQL Select Arithmetic Query:USE mydatabase; SELECT (5 + 12) AS "5 plus 12 is"

SQL Arithmetic Results:5 plus 12 is 17

SQL - Operators

SQL operators are found in just about every SQL query. Operators are the mathematical and equality symbols used to compare, evaluate, or calculate values. Equality operators include the (), and (=) symbols, which are used to compare one value against another. Each of these characters have special meaning, and when SQL comes across them, they help tell SQL how to evaluate an expression or conditional statement. Most operators will appear inside of conditional statements in the WHERE claus SQL Commands. Advertise on Tizag.com

Operators come in three flavors: mathematical, logical, and equality. Mathematical operators add, subtr multiply, and divide numbers. Logical operators include AND and OR. Take note of the following table future reference.

SQL operators are generally found inside of queries-- more specifically, in the conditional statements o WHERE clause.

SQL Equality Operator Query:USE mydatabase; SELECT customer,day_of_order FROM orders WHERE day_of_order > '7/31/08'

Sql Equality Operator:

customer day_of_order Tizag 2008-08-01 00:00:00.000 Tizag 2008-08-01 00:00:00.000 In this case, we've used the equality operator greater than (>) to return orders from the orders table wit date greater than '7/31/08'.

SQL - Equality Operator Table

Equality involves comparing two values. To do so requires the use of the (), or (=) special charact Does X = Y? Is Y < X? These are both questions that can be answered using a SQL Equality Operator expression.

SQL Equality Operators:Operator

SQL - Create

SQL CREATE is the command used to create data objects, including everything from new databases a tables to views and stored procedures. In this lesson, we will be taking a closer look at how table crea is executed in the SQL world and offer some examples of the different types of data a SQL table can ho such as dates, number values, and texts. Advertise on Tizag.com

To accomplish this, it is best to first take a look at the entire CREATE TABLE query and then review e line individually.

SQL Create Table Code:USE mydatabase; CREATE TABLE inventory ( id INT IDENTITY(1,1) PRIMARY KEY, product VARCHAR(50) UNIQUE, quantity INT, price DECIMAL(18,2) );

Line 1 identifies the scope of the query specifying a target database for query execution (USE mydatab and we've seen it before so let's skip ahead to the next line, line 2 (CREATE TABLE inventory). This li informs SQL of the plan to create a new table using the CREATE clause and specifies the name of the table (inventory). In this case, we plan on creating an inventory table to maintain a current inventory of items for an imaginary e-commerce web site.

SQL Create Line 3:id INT IDENTITY(1,1) PRIMARY KEY,

Line 3 should appear more foreign as there is a lot of information embedded in this line, but it is not as as it seems. This is the first line that declares how to set up the first table column inside the new invento table.

id = The name of this new table column. INT = The data type. INT is short for integer.

The first word, id, is the name of this new column and the second word declares the data type, INT (integers). SQL will now expect this table column to house only integer data type values.

IDENTITY (1,1) = The id column will be an identity column.

The next phrase, IDENTITY (1, 1) is a very special attribute and when a table column is marked as an identity column, the column essentially turns into an automated counter. As new rows are inserted into

SQL - Insert

To use the INSERT command, we must first have an understanding of where we would like to insert da and what types of data we want to insert. Do we plan on inserting numbers? Strings? Files? Let's return the orders table we created in an earlier lesson. Advertise on Tizag.com

SQL tables store data in rows, one row after another. The INSERT command is the command used to in new data (a new row) into a table by specifying a list of values to be inserted into each table column. T arrangement of values is important, and how they are arranged in the code corresponds to how the data values will be arranged in the the SQL table.

id - (identity, integer) customer - (customer name, character string) day_of_order - (date value) product - (name of product, character string) quantity - (quantity, integer)

Looking at the column names alone will give you an idea of what type of data each column is expected hold. The quantity column, for example, is expecting a number or integer of some sort and the day_of_ column is expecting a date value to be inserted.

SQL Insert Query:USE mydatabase; INSERT INTO orders (customer,day_of_order,product, quantity) VALUES('Tizag','8/1/08','Stapler',1);

SQL Insert Results:

(1 row(s) affected) You may notice that the id column has been left out of the query statement. The reason behind this is th when we created the orders table, we gave the id column a unique attribute called identity. SQL handle identity columns automatically for us and therefore, we do not need to manually insert data into this co

The first value Tizag corresponds with the customer table column. This ensures SQL will insert this val into the corresponding table column.

Now when we run the SELECT (*) query, SQL should return two rows with our statement instead of on single row.

Verification Query:USE mydatabase;

SQL - And

SQL AND links together two or more conditional statements for increased filtering when running SQL commands. AND helps the developer query for very specific records while answering questions like, "I to view all orders made by a certain customer AND made on a special date." There is no limit to the nu of AND/OR conditions that can be applied to a query utilizing the WHERE clause. This makes it possi for the developer to be as precise as needed when querying for results. Advertise on Tizag.com

SQL And Code:USE mydatabase; SELECT * FROM orders WHERE customer = 'Tizag' AND day_of_order = '08/01/08' AND product = 'Pen';

SQL Results:

id customer day_of_order product quantity 1 Tizag 2008-08-01 00:00:00.000 Pen 4 This example illustrates how SQL AND combines multiple conditional statements (3 total now) into a s condition with multiple circumstances (filters). Each filter removes rows from the result set that doesn't the condition.

SQL - Or

SQL OR also applies logic to help filter results. The difference is that instead of linking together condit statements, an OR condition just asks SQL to look for 2 separate conditions within the same query and return any records/rows matching either of the conditions.

SQL Or Code:USE mydatabase;

SQL - Between

BETWEEN is a conditional statement found in the WHERE clause. It is used to query for table rows th meet a condition falling between a specified range of numeric values. It would be used to answer quest like, "How many orders did we receive BETWEEN July 20th and August 5th?"

SQL Select Between:USE mydatabase; SELECT * FROM orders WHERE day_of_order BETWEEN '7/20/08' AND '8/05/08';

SQL Results:

id customer day_of_order product quantity 1 Tizag 2008-08-01 00:00:00.000 Pen 4 2 Tizag 2008-08-01 00:00:00.000 Stapler 1 5 Tizag 2008-07-25 00:00:00.000 19" LCD Screen 3 6 Tizag 2008-07-25 00:00:00.000 HP Printer 2 BETWEEN essentially combines two conditional statements into one and simplifies the querying proce for you. To understand exactly what we mean, we could create another query without using the BETWE condition and still come up with the same results, (using AND instead).

SQL Select Between:

SQL - Order By

ORDER BY is the SQL command used to sort rows as they are returned from a SELECT query. SQL o by command may be added to the end of any select query and it requires at least one table column to be specified in order for SQL to sort the results. Advertise on Tizag.com

SQL Order by query:USE mydatabase; SELECT * FROM orders WHERE customer = 'Tizag' ORDER BY day_of_order;

Executing this query should offer a list of orders made by Tizag and you may noticed that the result set now been sorted (low to high) according to the date value. In other words, the oldest order to the newes order.

SQL Results:id customer day_of_order product quantity 5 Tizag 2008-07-25 00:00:00.000 19" LCD Screen 3 6 Tizag 2008-07-25 00:00:00.000 HP Printer 2 1 Tizag 2008-08-01 00:00:00.000 Pen 4 2 Tizag 2008-08-01 00:00:00.000 Stapler 1

SQL - Update

SQL UPDATE is the command used to update existing table rows with new data values. UPDATE is a powerful command in the SQL world. It has the ability to update every single row in a database with th execution of only a single query. Due to UPDATE's supreme authority, it is in your best interest to alw include a WHERE clause when working with UPDATE query statements. That way, you will not accidentally update more rows than you intend to. Advertise on Tizag.com

Execute the following UPDATE command to update the customer orders table. Since we've provided a WHERE condition with this update command, this update will only modify rows that match the condit and in this case it happens to be order number 1 made by Tizag. This update should increase the quantit from 4 Pens to 6 Pens for Tizag's first order.

SQL Update Query:USE mydatabase; UPDATE orders SET quantity = '6' WHERE id = '1'

SQL Results:(1 row(s) affected) Let's verify our results by selecting this row from the orders table.

SQL Verification Query:USE mydatabase; SELECT * FROM orders WHERE id = '1'

SQL Results:id customer day_of_order product quantity 1 Tizag 2008-08-01 00:00:00.000 Pen

SQL - Alter

SQL ALTER is the command used to add, edit, and modify data objects like tables, databases, and view ALTER is the command responsible for making table column adjustments or renaming table columns. table columns can also be added and dropped from existing SQL tables. Advertise on Tizag.com

SQL Add:USE mydatabase; ALTER TABLE orders ADD discount VARCHAR(10);

SQL Results:id customer day_of_order product quantity discount 1 Tizag 2008-08-01 00:00:00.000 Pen 8 NULL 2 Tizag 2008-08-01 00:00:00.000 Stapler 3 NULL 3 A+Maintenance 2008-08-16 00:00:00.000 Hanging Files 14 NULL 4 Gerald Garner 2008-08-15 00:00:00.000 19" LCD Screen 5 NULL

SQL - Distinct

SQL SELECT DISTINCT is a very useful way to eliminate retrieving duplicate data reserved for very specific situations. To understand when to use the DISTINCT command, let's look at a real world exam where this tool will certainly come in handy. Advertise on Tizag.com

If you've been following along in the tutorial, we have created an orders table with some data inside tha represents different orders made by some of our very loyal customers over a given time period. Let's pr that we have just heard word from our preferred shipping agent that orders made in August require no shipping charges, and we now have to notify our customers. We do not want to send mailers to all of ou customers, just the ones that have placed orders in August. Also, we want to avoid retrieving duplicate customers as our customers may have placed more than one order during the month of August. We can write a very simple SQL query to extract this information from the orders table:

SQL Select Distinct:USE mydatabase; SELECT DISTINCT customer FROM orders WHERE day_of_order BETWEEN '7/31/08' AND '9/1/08';

SQL Results:

customer A+Maintenance Gerald Garner Tizag Running this query yields a list of all the customer's affected by our unexpected news from the shipping agency. With this list, we can now go about contacting each of these customers and informing them of t good news without worrying about contacting the same customer multiple times.

SQL - Subqueries

Subqueries are query statements tucked inside of query statements. Like the order of operations from y high school Algebra class, order of operations also come into play when you start to embed SQL comm inside of other SQL commands (subqueries). Let's take a look at a real world example involving the ord table and figure out how to select only the most recent order(s) in our orders table. Advertise on Tizag.com

To accomplish this, we are first going to introduce a built-in SQL function, MAX(). This function wrap around a table column and quickly returns the current highest (max) value for the specified column. We going to use this function to return the current "highest", aka most recent date value in the orders table.

SQL Subquery Preview:USE mydatabase; SELECT MAX(day_of_order) FROM orders

SQL Results:

day_of_order 2008-08-16 00:00:00.000 Now we can throw this query into the WHERE clause of another SELECT query and obtain the results our little dilemma.

SQL Select Subquery Code:USE mydatabase; SELECT * FROM orders WHERE day_of_order = (SELECT MAX(day_of_order) FROM orders)

:id customer day_of_order product quantity 3 A+Maintenance 2008-08-16 00:00:00.000 Hanging Files

SQL - Join

SQL JOIN joins together two tables on a matching table column, ultimately forming one single tempor table. The key word here is temporary. The tables themselves remain intact, and running a JOIN query not in any way change the data or table structure. JOIN is another way to select specific data from two more relational tables. Advertise on Tizag.com

In order to perform a JOIN query, we need a few pieces of information: the name of the table and table column we want to join on and a condition to meet for the JOIN to happen. This should sound a little confusing as there is much going on in a JOIN query, so let's take a look at an example:

SQL Join Query Code:USE mydatabase; SELECT * FROM orders JOIN inventory ON orders.product = inventory.product;

SQL Join Results:id customer day_of_order product quantity id product quantity price 1 Tizag 2008-08-01 00:00:00.000 Hanging Files 11 5 Hanging Files 33 14.99 2 Tizag 2008-08-01 00:00:00.000 Stapler 3 4

SQL - In

SQL IN is an operator used to pull data matching a list of values. A scenario where this proves useful w be if we wanted to retrieve customer data for two or more customers. We can use the IN operator to spe a list of customer names, and SQL will retrieve rows reflecting every customer in the list. Advertise on Tizag.com

Inside the query statement itself, the word "IN" replaces the (=) operator after the WHERE declarative slightly alters the meaning as well. Instead of listing a single value, you may list multiple values and SQ will retrieve the results for each value listed.

SQL In:USE mydatabase; SELECT * FROM orders WHERE customer IN ('Gerald Garner','A+Maintenance');

SQL Results:

id customer day_of_order product quantity 3 A+Maintenance 2008-08-16 00:00:00.000 Hanging Files 14 4 Gerald Garner 2008-08-15 00:00:00.000 19" LCD Screen 5 The results provide a list of all customer orders made by each of the customer names we have listed ins the IN clause ('Gerald Garner','A+Maintenance'). This is a great way to query for all orders made by a handful of different customers as we can see everything these particular customers have ordered thus fa

The real power of this condition comes to life when used with a subquery that retrieves a list of values. Running any SELECT query returns results in list format. And as we mentioned just a few short mome ago, this list can then be passed as a list for the IN clause using a subquery.

Let's adjust the previous example to only retrieve only the products column, as opposed to retrieving al columns (*).

SQL - CaseSQL CASE is a very unique conditional statement providing if/then/else logic for any ordinary SQL command, such as SELECT or UPDATE. It then provides when-then-else functionality (WHEN this condition is met THEN do_this). Advertise on Tizag.com This functionality provides the developer the ability to manipulate the presentation of the data without actually updating or changing the data as it exists inside the SQL table.

SQL Select Case Code:USE mydatabase; SELECT product, 'Status' = CASE WHEN quantity > 0 THEN 'in stock' ELSE 'out of stock' END FROM dbo.inventory;

SQL Results:

product Status 19" LCD Screen in stock HP Printer in stock Pen in stock Stapler in stock Hanging Files in stock Laptop in stock Using the CASE command, we've successfully masked the actual value of the product inventory withou actually altering any data. This would be a great way to implement some feature in an online catalog to allow users to check the status of items without disclosing the actual amount of inventory the store curr has in stock.

SQL - Case: Real World Example

As a store owner, there might be a time when you would like to offer sale prices for products. This is a perfect opportunity to write a CASE query and alter the inventory sale prices at the presentation level r

SQL - Group By

SQL GROUP BY aggregates (consolidates and calculates) column values into a single record value. GROUP BY requires a list of table columns on which to run the calculations. At first, this behavior will resemble the SELECT DISTINCT command we toyed with earlier. Advertise on Tizag.com

SQL Group By:USE mydatabase; SELECT customer FROM orders GROUP BY customer;

SQL Results:

customer A+Maintenance Gerald Garner Tizag Here, SQL has consolidated like values and returned those that are unique. In this case, we have actuall duplicated the behavior of SELECT DISTINCT, but you have also seen firsthand how GROUP BY acc a table column as a list and consolidates like customer values.

To unleash the true power of GROUP BY, it is necessary to include at least one mathematical (aggregat function, and to do so we will utilize the SUM() function to calculate how many total items have been purchased by each of our customers.

SQL Code:USE mydatabase; SELECT customer, SUM(quantity) AS "Total Items" FROM orders GROUP BY customer;

SQL Results:customer Total Items A+Maintenance 14 Gerald Garner 5 Tizag

SQL - ViewsSQL VIEWS are data objects, and like SQL Tables, they can be queried, updated, and dropped. A SQL VIEW is a virtual table containing columns and rows except that the data contained inside a view is generated dynamically from SQL tables and does not physically exist inside the view itself. Advertise on Tizag.com

SQL Create View Code:CREATE VIEW virtualInventory AS SELECT * FROM inventory;

With a successful execution of this query, we have now created a view data object of the inventory tab The virtualInventory view is considered a data object (like a table) and is now accessible to us the deve Views can be queried exactly like any other SQL table.

SQL View Code:USE mydatabase; SELECT * FROM virtualInventory;

SQL Results:id product quantity price 1 19" LCD Screen 25 179.99 2 HP Printer 9 89.99 3 Pen 78 0.99 4 Stapler 3 7.99

SQL - Dates

Date values are stored in date table columns in the form of a timestamp. A SQL timestamp is a record containing date/time data, such as the month, day, year, hour, and minutes/seconds. It's not much differe from the standard date format. Advertise on Tizag.com

Date Columns:

Column Type Format time HH:MM:SS date YYYY-MM-DD datetime YYYY-MM-DD HH:MM:SS Date values are stored in the form of a timestamp, and SQL offers a built-in function called GETDATE that returns the current date in the form of a SQL timestamp.

SQL SELECT GETDATE():USE mydatabase; SELECT GETDATE();

Timestamp Result:

2004-06-22 10:33:11.840 SQL expects dates to be formatted as above but does offer some flexibility when working with dates in query statements. For instance, date values do not necessarily need to contain the hour, minutes, and se values. SQL also accepts most traditional date formats such as "MM/DD/YY" (ex: "01/01/06").

Using a built in function, ISDATE() we can do some testing on date values to see if they meet the form requirements.

SQL Code:USE mydatabase; SELECT ISDATE('8/24/08') AS "MM/DD/YY", ISDATE('2004-12-01') AS "YYYY/MM/DD";

ISDATE() returns a 1 or a 0 indicating a true or false result. In this case, both formats are acceptable da

SQL - DatepartAdvertise on Tizag.com

DATEPART() is a SQL function used to extract all kinds of date information from timestamps, and it is function that is unique to Microsoft's SQL Server Application.

SQL Datepart:USE mydatabase; SELECT DATEPART(year, '2007-06-01') AS "Year";

SQL Results:Year 2007 DATEPART() requires 2 parameters separated by a comma (,). The first parameter specifies what type date data will be extracted, and the second parameter is a timestamp value.

SQL Datepart:USE mydatabase; SELECT DATEPART(year, '2007-06-01') AS "Year", DATEPART(month, '2007-06-01') AS "Month", DATEPART(day, '2007-06-01') AS "Day", DATEPART(dayofyear, '2007-06-01') AS "DayofYear", DATEPART(weekday, '2007-06-01') AS "Weekday";

SQL Results:Year Month Day DayofYear Weekday 2007 6 1 152 6

Datepart Abbreviation Chart:DatePart Abbreviation

SQL - DateAdd()

DATEADD() is the SQL function used to add and increment date values. Hours, minutes, months, and can be added to any date value. In fact, dates can be added based on any type of date part discussed in t SQL DATEPART() lesson. Advertise on Tizag.com

SQL Code:USE mydatabase; SELECT DATEADD(year, 1, getdate()) AS "+1 Year";

SQL Results:

+1 Year 2009-06-31 00:00:00.000 This example shows how to use DATEADD() to take a specified date value and increment it by the 'yea date part. By replacing the middle parameter with a negative value, we can utilize the same DATEADD function to subtract dates as well.

SQL Code:USE mydatabase; SELECT DATEADD(day,-1, '2006-06-01') AS "-1 Day";

SQL Results:

-1 Day 2006-05-31 00:00:00.000 In each example, SQL is able to perform a calculation on each date value based on a timestamp, and aft the calculation, a timestamp value returned. Also note that the date parameter can be based on another S function or the result of a subquery.

SQL Code:USE mydatabase; SELECT DATEADD(day,-30, (SELECT MAX(day_of_order) FROM orders)) AS "-30 Days";

SQL Results:-30 Days

SQL - Delete Command(s)

In the SQL world, databases, rows, and columns all have one thing in common: once a DELETE statem has been executed successfully against them, the data they once contained is lost forever! Be very caref with these commands and be sure to properly backup all data before proceeding with any type of DELE command(s). Advertise on Tizag.com SQL offers several ways to tackle data deletion. Here are the differences.

SQL Delete Commands:DELETE - Deletes any number of rows from a data object. DROP - Removes table columns, tables, and all data objects SQL applications. TRUNCATE - Empties out data without removing the object itself.

SQL - Delete

DELETE queries work much like UPDATE queries and like UPDATE, it is much advised to always u WHERE condition when running any delete query or else you risk deleting too much data.

SQL Delete Query:USE mydatabase; DELETE FROM orders WHERE customer = 'A+Maintenance';

SQL Results:1 Row(s) affected

SQL - Truncate

SQL TRUNCATE is the fastest way to remove all data from a SQL table, leaving nothing but an empty shell. You might choose to use this command when all the data inside of a table needs to be removed bu you'd like the table column definitions to remain intact.

SQL Truncate Table Code:USE mydatabase; TRUNCATE TABLE orders;

SQL - Union

SQL UNION combines two separate SQL queries into one result set. A JOIN statement adds additiona table columns to a result set (horizontally), UNION combines row results from one table with rows of another table (vertically). Advertise on Tizag.com

In order to perform a UNION the columns of table 1 must match those of table 2. This rule ensures that result set is consistent as rows are fetched by SQL.

For these next exercises we suggest creating two different tables that are identical in structure but conta unique rows of data. We challenge you to do this by reviewing the SQL Create queries and modifying t to create two brand new employee tables.

SQL Select Union Code:USE mydatabase; SELECT * FROM employees UNION SELECT * FROM employees2;

SQL Table:ID Lastname Firstname Title 1 Johnson David crew 2 Hively Jessica crew 9 Hicks Freddy crew 10 Harris Joel crew 11 Davis

SQL - Syntax - (Speaking SQL)

Syntax, by definition, means the study of linguistic rules and patterns. Every programming language, including SQL, must follow a unique set of guidelines termed syntax. Punctuation, spaces, mathematic operators, and special characters have special meaning when used inside of SQL commands and query statements. For example, each and every SQL command will end with a semi colon (;). Advertise on Tizag.com

Executing SQL commands that do not have proper syntax and formatting will result in a syntax error. S errors might be the most common and first error messages new SQL developers will experience. Let's now take a look at a very simple SQL command that will be used in just about every example contained in this tutorial from here on out.

Sample SQL Command:use mydatabase;

This command identifies a database as a target database, meaning that any SQL command or query exe after this line will be run against the identified database. In this case, the database 'mydatabase' will be target database. This is a good way to prevent mistakes and avoid potential data loss and a good reason include this command into each and every authored SQL query.

SQL - Syntax: Capitalization and Spacing

In some programming languages, capitalizing commands or excessive spacing may or may not cause sy code errors and cause the command to fail. SQL syntax is very loose when it comes to capitalization an spacing, allowing a lot of room for the developer to decide on his/her own preference in regards to capitalization and spacing.

Let's rewrite the same SQL command from the previous example and take advantage of SQL's loose sy characteristics.

Sample SQL Command:USE mydatabase;

The example above, though it does look different due to the capitalization and spacing, will yield the sa results as the first example.

SQL - Syntax: Building good habits

SQL - Data Types

SQL data takes shape in several different forms, including character strings, numbers, file stores, and d SQL developers call the shots as to what types of data will be stored inside each and every table column when creating a SQL table. The developer must specify the column type of each new SQL table column Advertise on Tizag.com

Column types are synonymous with data types as the column type is what designates the type of data th will be stored inside the column. In other words, a SQL data type is a label and a guideline for SQL to understand what type of data is expected inside of each table column and this identifies how SQL will interact with the stored data. Below, we will give you an overview on the types of data that can be store within a SQL table.

SQL - Numbers, Decimals, and DatesData Types:

Integers - (3, -17) Point(Decimal) - (3.23415) Date - (2004-06-22 10:33:11.840)

Storing numbers and decimals allows the developer to collect statistical data and create reports based o data contained inside the table. SQL can even perform mathematical calculations against numeric data, providing endless number-crunching abilities. In SQL, decimals are often referred to as point or floating-point numbers. These data types are slightly different from the normal 'integer' data types.

For the most part, date values are treated like numbers and they can even be added together and subtrac offering the developer the option to add days, months, or years together to create new dates (more on th later). Additionally, specific data can be extracted from date values, allowing the developer to pull spec date information from a date value like only the month number, the year, or the day of the week.

SQL - Boolean Data

("TRUE" / "FALSE") (1/0)

Boolean values are true/false types of data. A Boolean table column will contain either string values of "True" and "False" or the numeric equivalent representation, with 0 being false and 1 being true.

SQL - Character Strings

SQL - Expressions

SQL Expressions are the pieces of a SQL query that compare values against other values or perform arithmetic calculations. Expressions can be found inside of any SQL command usually in the form of a conditional statement. In the SQL world, conditional statements and expressions test or compare val against other values. Advertise on Tizag.com

SQL - Boolean ExpressionsBoolean expressions return rows (results) when a single value is matched.

SQL Boolean Expression:USE mydatabase; SELECT * FROM orders WHERE id = '1';

SQL Results:id customer day_of_order product quantity 1 Tizag 2008-08-01 00:00:00.000 Pen 4

SQL - Numeric ExpressionNumeric Expressions return a single numeric value instead of an entire row and usually perform calculations.

SQL Code:USE mydatabase; SELECT 15 + 4;

SQL Code: