Sql null

Data validation using SQL Coalesce function

In the following example, we are going to find the emergency employee contacts. Usually, in any organization, the employee’s phone numbers are listed under work, home, cell phone columns.

Let us see how to find employees where no emergency contacts are listed or, in other words, let’s pull all the details of the employee with emergency contacts.

In the following example, the tb_EmergencyContact holds the contact numbers of all employees.

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DROPTABLEIFEXISTStb_EmergencyContact; CREATETABLEtb_EmergencyContact  ( empidint, firstnameVARCHAR(100)NOTNULL, lastnameVARCHAR(100)NOTNULL, relationshipVARCHAR(100), homephoneVARCHAR(25), workphoneVARCHAR(25), cellphoneVARCHAR(25) ); INSERTINTOtb_EmergencyContact (empid,firstname,lastname,relationship,homephone,workphone,cellphone) VALUES(1, ‘Ambika’, ‘Prashanth’, ‘Wife’, NULL, ‘920.176.1456’, ‘928.132.2967’),(2, ‘Prashanth’, ‘Jayaram’, ‘spouse’, NULL, NULL, ‘982.132.2867’), (3, ‘Pravitha’, ‘Prashanth’, ‘Daughter’, NULL, NULL, NULL)

The SQL Coalesce function is used to select the columns homephone, workphone, and cellphone. In case of NULL values, the value ‘NA’ (not applicable), a literal string is returned.

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SELECT firstname+»+lastnamefullname, relationship, COALESCE(homephone,workphone,cellphone,’NA’)phone FROM dbo.tb_EmergencyContact

SQL COALESCE examples

Assuming that we have a table with the following structure and data:

Using SQL COALESCE for substituting NULL values

When working with the data in the database table, you often use the function to substitute a default value for a  value.

Suppose you have to display the products on a web page with all information in the table. Some products may not have the summary but the other do.

In this case, you can use the function to return the product summary, and if the product summary is not provided, you get the first 50 characters from the product description.

You can use the function to add the (…) to the end of the excerpt to make it more meaningful to users that the text they are reading is just the excerpt and there is more content if they click the read more link.

Using SQL COALESCE function in expression

Suppose you need to calculate the net price of all products and you came up with the following query:

The net price is for the . This is because the discount of this product is , and when you use this value in the calculation, it results in a value.

To fix this, you can update all values in the column to 0.

Or you can use the function as follows:

The net price is now calculated correctly.

SQL ISNULL function Examples

Simple String Evaluation example

In above query we used SQL ISNULL function to check given first argument expression is NULL or not, it starts evolution from first argument which is NULL so it checks for second argument that is a string ‘Hello’ so it will return ‘Hello’ as a replacement Value

OUTPUT:

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SQL ISNULL function example with Integer arguments

In successive query also we apply SQL ISNULL function to check for NULLABLE value in first parameter which is NULL so it will return second parameter integer value of 100 as result

OUTPUT:

SQL ISNULL function example with NULL as Second Argument

In Previous query SQL ISNULL function is used to test NULL value in first argument, Having NULL value as second argument do not affect result, it will return value of first argument as ‘SQL functions’

OUTPUT:

SQL ISNULL function examples with column name as argument

Consider school database with two tables for examples of SQL ISNULL function

Student Table

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student_id	studentname	admissionno	admisssiondate	enrollmentno	date_of_birth	email	city	class_id
101	reema	10001	02-02-2000	e15200002	02-03-1990	[email protected]		2
102	kriya	10002	04-05-2001	e16200003	04-08-1991	[email protected]		1
103	meena	10003	06-05-1999	e15200004	02-09-1989		Vadodara	3
104	carlin	2001	04-01-1998	e14200001	04-04-1989	[email protected]	Vapi	1
105	dhiren	2002	02-02-1997	e13400002	02-03-1987	[email protected]	Surat	2
106	hiren	2003	01-01-1997	e13400001	03-03-1987	[email protected]		2
107	mahir	10004	06-09-2000	e15200003	07-09-1990		Vapi	3
108	nishi	2004	02-04-2001	e16200001	03-02-1991	[email protected]	Vadodara	1

Result Table

result_id	student_id	examname	examdate	subjectid	obtainmark	totalmarks	percentage	grade	status
3001	101	sem1	07-08-2001	1	80	100	80	A+	pass
3002	101	sem1	08-08-2001	2	76	100	76	A+	pass
3003	102	sem3	05-05-2000	3	67	100	67	A	pass
3004	102	sem3	06-05-2000	4	89	100	89	A+	pass
3005	102	sem3	07-05-2000	5	90	100	90	A+	pass
3006	103	sem5	08-09-1998	6	55	100	55	B	pass
3007	105	sem3	09-09-2001	2	78	100	78	A+	pass

Use SQL ISNULL function to check city column values for all students, if it is NULL than replace it with ‘Surat’

In above SQL query checks city column value using ISNULL function for NULL, and replace it with Surat.

OUTPUT:

SQL Coalesce and Computed columns

The following example uses SQL COALESCE to compare the values of the hourlywage, salary, and commission columns and return only the non-null value found in the columns.

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CREATETABLEEMP (EMPNOINTNOTNULL, ENAMEVARCHAR(20), JOBVARCHAR(10), MGRINT, JOINDATEDATETIME, HOURLYWAGEDECIMAL(7,2), SALARYDECIMAL(7,2), COMMISSIONDECIMAL(7,2), NUMSALESDECIMAL(7,2), DNOINT) INSERTINTOEMPVALUES(7369,’SMITH’,’CLERK’,7902,’02-MAR-1970′,NULL,8000,NULL,20,2), (7499,’ALLEN’,’SALESMAN’,7698,’20-MAR-1971′,NULL,1600,3000,4,3), (7521,’WARD’,’SALESMAN’,7698,’07-FEB-1983′,40,1250,5000,10,3);

The following T-SQL is used to list the total salary paid to all the employees

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SELECTEMPNO,ENAME,CAST(COALESCE(HOURLYWAGE*40*52, salary, Salary+(COMMISSION*NUMSALES))ASdecimal(10,2))ASTotalSalary FROMdbo.EMP ORDERBYTotalSalary;

Now, Let us see an example to create a computed column with SQL Coalesce function in SQL Server

In general, we may need to use the expression in the tables. In tables, it is required to compute the values that are often calculated using several existing columns and with few scalar values of the table. Also, these columns are dependent on one or more other columns. In this way, we can create a computed column using the Coalesce SQL function so that NULL values are efficiently handled.

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ALTERTABLEdbo.EMP ADDTotal_SalaryAS CAST(COALESCE(HOURLYWAGE*40*52, salary, Salary+(COMMISSION*NUMSALES))ASdecimal(10,2)) select*fromEMP

Now, you can see that a simple SELECT statement displays the pre-calculated results.

Coalesce Pivoting

You need to use the example below to locate connections with emergency workers. Telephone numbers for employees normally appear in each company’s work, home, and cell phone columns.

You need to see how to find employees who have no emergency connections or, in other words, how to obtain all the details about an emergency employee.

DROP TABLE IF EXISTS STATE;

CREATE TABLE STATE

CITY VARCHAR(50),

STATE VARCHAR(500))

INSERT INTO STATE VALUES

(‘Appleton’,’WI’),(‘Milwaukee’,’WI’),(‘Madison’,’WI’),(‘Miami’,’Florida’),(‘Jacksonville’,’Florida’)

DECLARE @col nvarchar(MAX);

SELECT @col = COALESCE(@col,») +»»+CITY +»»+ ‘,’ 

FROM dbo.STATE WHERE state = ‘WI’;

SELECT substring(@col,1,len(@col)-1)

Примеры использования

Синтаксис у выражения Coalesce предельно прост, однако важно не забывать, что результатом выполнения команды станет ПЕРВОЕ непустое найденное значение из списка аргументов. Это замечание имеет очень большое значение, поэтому аргументы в выражении необходимо расставлять в порядке их важности

Проще всего понять принцип по таблице площадей. Составьте запрос, выбирающий наименование объекта недвижимости, а также значение площади:

SELECT Area.id, Area.object_name, coalesce(Area.area_yt, Area.area_decl)

И получите результат:

По объектам «Здание 1», «Земельный участок 1» и «Сооружение 2» были заполнены оба значения площади, но в приоритете оказалась площадь уточненная, поскольку ее мы указали в списке аргументов первой. Выражение Coalesce нашло первое непустое значение и вывело его, прекратив дальнейший просмотр аргументов. Данное построение запроса — верное, ведь уточненная площадь более определенная, нежели декларированная. Если бы мы указали в качестве первого аргумента площадь декларированную, то при заполненности этого поля таблицы она оказалась бы в приоритете.

Помимо использования в Select, очень часто выражение Coalesce применяется с условием Where. Оно позволяет отсечь из результата те строки, в которых значения перечня полей пустые (или наоборот, включить в результат только те значения, где перечень полей не заполнен). Данная ситуация встречается повсеместно: например, на предприятии при оформлении нового сотрудника в базу данных внесли только базовые сведения о нем, а заполнение подробной информации оставили «на потом». Постепенно «пробелы» всплывают — или перед проверкой, или при направлении сотрудника в отпуск/командировку/больничный.

Выберем из таблицы с основными характеристиками объекты недвижимости, у которых не заполнено ни одно из значений характеристик:

Надеемся, что наше подробное Coalesce sql описание помогло вам понять все особенности использования данного выражения, а также разобраться с важными нюансами.

Solutions

MySQL

The MySQL function lets you
return an alternative value if an expression is NULL:

SELECT ProductName, UnitPrice * (UnitsInStock + IFNULL(UnitsOnOrder, 0))
FROM Products;

or we can use the function, like this:

SELECT ProductName, UnitPrice * (UnitsInStock + COALESCE(UnitsOnOrder, 0))
FROM Products;

SQL Server

The SQL Server function lets
you return an alternative value when an expression is NULL:

SELECT ProductName, UnitPrice * (UnitsInStock + ISNULL(UnitsOnOrder, 0))
FROM Products;

or we can use the
function, like this:

SELECT ProductName, UnitPrice * (UnitsInStock + COALESCE(UnitsOnOrder, 0))
FROM Products;

MS Access

The MS Access function returns
TRUE (-1) if the expression is a null value, otherwise FALSE (0):

SELECT ProductName, UnitPrice * (UnitsInStock + IIF(IsNull(UnitsOnOrder), 0, UnitsOnOrder))
FROM Products;

Oracle

The Oracle function achieves the same result:

SELECT ProductName, UnitPrice * (UnitsInStock + NVL(UnitsOnOrder, 0))
FROM Products;

or we can use the
function, like this:

SELECT ProductName, UnitPrice * (UnitsInStock + COALESCE(UnitsOnOrder, 0))
FROM Products;

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Comparison SQL ISNULL() V/S SQL Coalesce() Functions

• SQL ISNULL function is one of the T-SQL function where T-SQL is transact-SQL is the proprietary form of SQL used by Microsoft SQL Server, whereas SQL Coalesce function is based on ANSI SQL
• SQL IS NULL function contains only two parameters whereas SQL Coalesce function can have multiple parameters, if we want to used SQL ISNULL function with multiple parameters, we need to used it as Nested SQL ISNULL function

Examples of similarity between ISNULL() and Coalesce()

Above both queries show similarities between Coalesce and IsNull function, both queries give same result when we execute it.

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OUTPUT:

Example of difference between ISNULL() and Coalesce()

When we execute above both queries,

• first query with Coalesce function will return error message ‘At least one of the arguments to COALESCE must be a typed NULL’
• Second query with ISNULL function will return NULL as return

OUTPUT:

Above both queries will give same result as 10, but the way to write arguments to evaluate is difference, we can give more arguments with Coalesce function whereas with IsNULL we can give only two arguments.

OUTPUT:

Функции TO_NUMBER и TO_DATE

Функция преобразования строки в дату TO_DATE (строка, формат). Возможные значения форматов уже рассмотрены выше, поэтому приведу несколько примеров использования данной функции. Примеры:

SELECT
TO_DATE («01.01.2010″, `DD.MM.YYYY») FROM
DUAL вернет дату `01.01.2010″;

SELECT
TO_DATE («01.JAN.2010″, `DD.MON.YYYY») FROM
DUAL вернет дату `01.01.2009″;

SELECT
TO_DATE («15-01-10″, `DD-MM-YY») FROM
DUAL вернет дату `15.01.2010″.

Функция преобразования строки в числовое значение TO_NUMBER (строка, формат). Самые распространенные значения форматов перечислены в таблице, поэтому рассмотрим применение данной функции на примерах. Примеры:

SELECT
TO_NUMBER (`100″) FROM
DUAL вернет число 100 SELECT TO_NUMBER (`0010.01″, «9999D99″) FROM
DUAL вернет число 10.01;

SELECT
TO_NUMBER («500,000», «999G999») FROM
DUAL вернет число 500000.

Overview of SQL ISNULL Function

SQL ISNULL is a function which is used to check or to replace Null value of specified column or expression which is the first parameter of the function, if it is null than the function will return second parameter value as alternative or replaced value, and if first parameter value is not null than function will return the same.

SQL ISNULL is Advanced SQL function which takes two parameters first one is expression or column name and second is value which is return if expression or column contains NULL value

What are NULL values and NULL functions in SQL?

Null values the missing data in SQL tables it is like placeholders in the database where data ins not available, NULL value is not a part of any SQL datatype, column having any datatype can have NULL value.

Null functions are required to perform operations on the null values stored in database. We can apply functions on NULL values to check a value is null or not or to perform any operation on it.

Function	Description
ISNULL()	Used to check for NULL value in first argument and replace it with second argument value
IFNULL()	Returns the first argument value if it is NULL otherwise returns the second value
COALESCE()	Returns the first not NULL value from list of arguments
NVL()	used to replace NULL value with the desired value given by user

SQL ISNULL Syntax

• check_expression | column_name : It is specified expression or table column name which is to be checked for NULL or not
• value: The specified value which is to be returned as replace or alternate value, in case the expression is NULL

SQL ISNULL Return Type

Returns the same type as check_expression. If a literal NULL is provided as check_expression, returns the data type of the value. If a literal NULL is provided as check_expression and no value is provided, returns an int.

SQL IFNULL(), ISNULL(), COALESCE(), and NVL() Functions

All the Functions returns the specified value if the value in the specified column inside these function is . In other words, All these functions are used to check the value is or not, if the values are , then specified value is return.

Syntax of IFNULL Function

 function is used in MySQL.

Parameter Values of IFNULL() Function

Parameter	Description
expression	Required. The expression to test whether is NULL
alternate_value	Required. The value to return if an expression is NULL

Syntax of ISNULL Function

In MSSQL, Azure SQL Database, Azure SQL Data Warehouse, Parallel Data Warehouse, function is used.

Parameter Values of ISNULL() Function

Parameter	Description
expression	Required. The expression to test whether is NULL
alternate_value	Required. The value to return if an expression is NULL

Syntax of ISNULL Function used in MySQL

Parameter Values of ISNULL function used in MySQL

Parameter	Description
expression	Required. The expression to test whether is NULL or not, if an expression is NULL, then ISNULL function return 1, otherwise it returns 0.

MySQL COALESCE Function

MySQL COALESCE Function return the first non-NULL value of a list or return NULL if there are no non-NULL values in the list.

SQL Server ISNULL Function overview

We can replace NULL values with a specific value using the SQL Server ISNULL Function. The syntax for the SQL ISNULL function is as follow.

SQL Server ISNULL (expression, replacement)

• Expression: In this parameter, we specify the expression in which we need to check NULL values
• Replacement: We want to replace the NULL with a specific value. We need to specify replacement value here

The SQL Server ISNULL function returns the replacement value if the first parameter expression evaluates to NULL. SQL Server converts the data type of replacement to data type of expression. Let’s explore SQL ISNULL with examples.

Example 1: SQL Server ISNULL function in an argument

In this example, SQL ISNULL function returns the second argument value because the first argument is NULL:

1	SELECTISNULL(NULL,100)result;

In the following examples, we can see the following.

• If the first argument is NULL, it returns the value of the second argument.
• If the first argument is NOT NULL, it returns the first argument value as output.

1 2	SELECTISNULL(NULL,’SQLServer’)result; SELECTISNULL(‘SQLShack’,’SQLServer’)result;

Example 2: SQL Server ISNULL to replace a value in existing column values

At the beginning of this article, we created the Employee table and inserted NULL values in it. We can use SQL ISNULL to replace existing NULL values with a specific value.

For example, we want to return Employee salary 10,000 if it is NULL in the Employee table. In the following query, we used SQL ISNULL function to replace the value.

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SELECTEmployeeid, ISNULL(EmployeeSalary,10000)EmployeeSalary FROMEmployee;

Let’s update the NULL value in the Employee table using the following update statement.

1	UpdateEmployeesetEmployeeSalary=65656whereEmployeeID=2

We do not have any NULL value in the table now; therefore if we run the query with SQL Server ISNULL, it returns actual values of the rows.

Example 3: SQL Server ISNULL with aggregate functions

We can use SQL ISNULL with aggregate functions such as SUM, AVG as well. Suppose we want to perform sum of EmployeeSalary present in Employee table. If EmployeeSalary is NULL, it should be replaced with 10000 before adding the salaries.

Before we move, update the EmployeeSalary as NULL for EmployeeID 2 using the following query.

1	UpdateEmployeesetEmployeeSalary=NULLwhereEmployeeID=2

In the following query, we replaced the NULL value with value 10000 first and then performed SUM on it. You can visualize it with the following screenshot.

1 2	SELECTSUM(ISNULL(EmployeeSalary,10000)) FROMEmployee;

Similarly, we can use SQL ISNULL function to replace NULL values and calculate the average value with AVG() function.

1 2	SELECTAVG(ISNULL(EmployeeSalary,10000)) FROMEmployee;

Example 4: Difference between SQL Server ISNULL with IS NULL

You might confuse between SQL Server ISNULL and IS NULL. We use IS NULL to identify NULL values in a table.

For example, if we want to identify records in the employee table with NULL values in the Salary column, we can use IS NULL in where clause.

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SELECT* FROMEmployee WHEREEmployeeSalaryISNULL;

In the following screenshot, we cannot use SQL Server ISNULL to find NULL values. We use it to replace NULL values with a specific value. In the second part, we can see the employee having a NULL salary.

Example 5: SQL Server ISNULL to replace the NULL value with a custom message

Consider the example in which we have NULL values in DeliveryAddressLine2 column. We want to print a message in if the actual values from DeliveryAddressLine2 have NULL values.

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Select , , , , ISNULL(,’Address Same as DeliveryAddressLine1′)ASDeliveryAddressLine2, fromcustomers

You can see the message in DeliveryAddressLine2 column.

Introduction to the SQL COALESCE function

The function accepts a number of arguments and returns the first non-NULL argument. The following illustrates the syntax of the function.

The function evaluates its arguments from left to right. It stops evaluating until it finds the first non-NULL argument. It means that all the remaining arguments are not evaluated at all.

The function returns if all arguments are .

The following statement returns 1 because 1 is the first non-NULL argument.

The following statement returns because it is the first string argument that does not evaluate to .

If you use the following statement

you will get the division by zero error.

However, the following statement returns 1 and does not issue any error:

This is because the function is short-circuited. It stops evaluating the remaining arguments after it finds the first non-NULL arguments.

Almost all relational database systems support the function e.g., MySQL, PostgreSQL, Oracle, Microsoft SQL Server, Sybase.

Note that the function is the most generic function of the function and can be used instead of the function.

What is a NULL value?

Before we delve into how to navigate the potential minefield of datasets with missing values and avoid stepping on a Null, let’s first take a quick look at what a NULL is.

Null (or NULL) is a special marker used in Structured Query Language to indicate that a data value does not exist in the database. Introduced by the creator of the relational database model, E. F. Codd, SQL Null serves to fulfil the requirement that all true relational database management systems (RDBMS) support a representation of “missing information and inapplicable information”. Codd also introduced the use of the lowercase Greek omega (ω) symbol to represent Null in database theory. In SQL, NULL is a reserved word used to identify this marker. … This should not be confused with a value of 0. A null value indicates a lack of a value — a lack of a value is not the same thing as a value of zero in the same way that a lack of an answer is not the same thing as an answer of “no”.

Furthermore …

SQL does provide some handy functionality for working with your character data in your SQL queries that we’ll describe in detail

Conclusion

This blog explains effective tips and tricks on using Coalesce in SQL  features or Coalesce SQL Oracle effectively with T-SQL. Coalesce feature typically occurs in certain content like query, view, stored procedure, etc. The Coalesce in SQL can be used in a function to make it more general. By putting it in a computed column, you can improve its accuracy and make the results visible at all times.

This article provides plenty of details to use the Coalesce feature in various situations. Join the SQL certification program from Simplilearn and begin your database learning right now to learn more about the Coalesce in SQL  and other SQL concepts.

Have any questions for us? Leave them in the comments section of this article. Our experts will get back to you on the same, ASAP!

Oracle NVL Function

function is very similar to MySQL function and SQL Server . function is used to replace  value to a specified value.

Syntax of NVL Function used in Oracle

Parameter Values of NVL Function used in Oracle

Parameter	Description
expression	Required. The expression to test whether is NULL
alternate_value	Required. The value to return if an expression is NULL

Example:

Let us consider this table «Employee» for records.

Table Name: Employee

ID	EmpName	City	Country	Gender	Salary
1	Shankar	Delhi	India	male	25000
2	Sourabh	Delhi	India	male	30000
3	Ranvijay	Mumbai	India	male	15000
4	Kapil	Noida	India	male	25000
5	Shalini	Jaipur	India	female	18000
6	Rakesh	Faridabad	India	male	23000
7	Akshay	Mumbai	India	male	21000
8	Sarah	New York	US	female	76000
9	Rocky	Noida	India	male	28000

Example of MySQL IFNULL Function

For selecting records if City and Country is , then it returns «n/a», otherwise it returns City and Country using IFNULL function, the query will be:

Output

ID	EmpName	City	Country
1	Shankar	Delhi	India
2	Sourabh	Delhi	India
3	Ranvijay	Mumbai	India
4	Kapil	n/a	India
5	Shalini	Jaipur	India
6	Rakesh	Faridabad	India
7	Akshay	Mumbai	India
8	Sarah	n/a	n/a
9	Rocky	Noida	India

Example of SQL Server ISNULL Function

For selecting records if City and Country are , then it returns «n/a», otherwise it returns City and Country using function, the query will be:

Output

ID	EmpName	City	Country
1	Shankar	Delhi	India
2	Sourabh	Delhi	India
3	Ranvijay	Mumbai	India
4	Kapil	n/a	India
5	Shalini	Jaipur	India
6	Rakesh	Faridabad	India
7	Akshay	Mumbai	India
8	Sarah	n/a	n/a
9	Rocky	Noida	India

Example of MySQL ISNULL Function

For selecting records if City is , then it returns ‘0’, otherwise it returns ‘0’ and Country using MySQL function, the query will be:

Output

City

1

Example of MySQL COALESCE Function

For selecting records if City and Country are NULL, then it returns «n/a», otherwise it returns City and Country using function, the query will be:

Output

ID	EmpName	City	Country
1	Shankar	Delhi	India
2	Sourabh	Delhi	India
3	Ranvijay	Mumbai	India
4	Kapil	n/a	India
5	Shalini	Jaipur	India
6	Rakesh	Faridabad	India
7	Akshay	Mumbai	India
8	Sarah	n/a	n/a
9	Rocky	Noida	India

Example of Oracle NVLFunction

For selecting records if City and Country are , then it returns «n/a», otherwise it returns City and Country using  function, the query will be:

Output

ID	EmpName	City	Country
1	Shankar	Delhi	India
2	Sourabh	Delhi	India
3	Ranvijay	Mumbai	India
4	Kapil	n/a	India
5	Shalini	Jaipur	India
6	Rakesh	Faridabad	India
7	Akshay	Mumbai	India
8	Sarah	n/a	n/a
9	Rocky	Noida	India

Scalar user-defined function and SQL Coalesce function

A user-defined function is created to return a string specific to the provided input and then the output is grouped using a grouping clause. In the following example, the scalar valued function returns the concatenated string values separated by ‘,’ for a specified ‘City’ input. The following example returns an output where the state column is grouped and its cities values are concatenated and separated by a delimiter ‘,’ (comma). You can also user STRING_AGG if you’re using SQL Server 2017. You can refer more information with the article Top SQL string functions in SQL Server 2017

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CREATEFUNCTIONdbo.tfn_CoalesceConcat ( @statevarchar(100) ) RETURNSNVARCHAR(MAX) AS BEGIN DECLARE@strNVARCHAR(MAX); SELECT@str=COALESCE(@str+’, ‘,»)+CITY FROMdbo.STATE WHEREstate=@state ORDERBYstate; RETURN(@str); END GO

Here is how we call the function name dbo.tfn_CoalesceConcat in the select statement.

The output is a concatenated stream of values separated by a delimiter ‘,’

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SELECTstate,city=dbo.tfn_CoalesceConcat(state) FROMdbo.state GROUPBYstate ORDERBYstate;

Элемент RR в формате даты

Элемент формат даты и времени RR похож на элемент формате YY даты и времени, но это обеспечивает дополнительную гибкость для хранения значений даты и в других столетий. Элемент формата RR даты и времени позволяет хранить даты 20-го века в 21-м веке, указав только две последние цифры года.

Если две последние цифры текущего года являются 00 до 49, то возвращаемый год имеет те же первые две цифры, как в текущем году.

Если две последние цифры текущего года от 50 до 99, то первые 2 цифры возвращенного года являются 1 больше, чем в первые 2 цифр текущего года.

Если две последние цифры текущего года являются 00 до 49, то первые 2 цифры возвращенного года являются 1 меньше первых 2 цифр текущего года.

Если две последние цифры текущего года от 50 до 99, то возвращаемый год имеет те же первые две цифры, как в текущем году.

SQL Coalesce Function

The SQL server’s Coalesce function is used to handle the Null values. The null values are replaced with user-defined values during the expression evaluation process. This function evaluates arguments in a particular order from the provided arguments list and always returns the first non-null value.

Properties of the SQL Coalesce function and examples

• The data types of the expressions must be the same
• It can have multiple expressions in it
• Coalesce in SQL  is a syntactic shortcut for the Case expression in SQL
• An integer is always evaluated first, and an integer followed by a character expression produces an integer as an output

SELECT COALESCE (NULL,’Shobha’,’Shivakumar’)

Example 2:

SELECT COALESCE (NULL,’Shobha’, 10, ‘Shivakumar’)

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SELECT COALESCE (NULL, 10, ‘Shobha’, ‘Shivakumar’)

SELECT COALESCE (NULL, 10, 20, 30)

SELECT COALESCE (NULL, 20, 10, 30)

SQL COALESCE and CASE expression

The SQL COALESCE function can be syntactically represented using the CASE expression. For example, as we know, the Coalesce function returns the first non-NULL values.

SELECT COALESCE (expression1, expression2, expression3) FROM TABLENAME;

The above Coalesce SQL statement can be rewritten using the CASE statement.

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SELECT firstname+»+lastnamefullname, relationship, CASE WHENhomephoneisNOTNULLThenhomephone WHENcellphoneisNOTNULLThencellphone WHENworkphoneisNOTNULLThenworkphone ELSE’NA’ END EmergencyContactNumber FROM dbo.tb_EmergencyContact

The query returns the same result as the one that uses the COALESCE function.

SQL ISNULL function with Aggregate function

Aggregate function like AVG, SUM, MIN, MAX can be used with SQL ISNULL function, we can give result of SQL ISNULL as an input of Aggregate functions

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For example, to find average obtain marks of students, if obtain marks is NULL than replaced with 35 marks,

In previous query, first all NULL values of obtain marks column is replace with 35 and then AVG Aggregate function to the resulting set of all not null values

OUTPUT:

To find total of all obtained marks and to determine average percentage of students if none of the student have NULL and both column value

• On above query SQL ISNULL function is used as nested of AVG and SUM aggregate function
• Before finding average value of percentage, SQL ISNULL function will replace NULL value of percentage with 35, same as if obtained mark of any student is not exist, it will be replaced with 35 mark using SQL ISNULL

OUTPUT:

Introduction

We define the following parameters while designing a table in SQL Server

• Data types for a particular column
• Allow NULL or Not Null values in SQL Server

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CREATETABLEtable_name ( column1datatype, column2datatype, … );

If we do not provide any value for column allow NULL values, SQL Server assumes NULL as default value.

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CREATETABLEEmployee (EmployeeIDINTIDENTITY(1,1)NOT NULL, EmployeeNameVARCHAR(50)NOT NULL, EmployeeSalaryINTNULL );

Let’s insert a few records in the Employee table.

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INSERTINTOEmployee (EmployeeName, EmployeeSalary ) VALUES (‘Rajendra’, 55645 ); INSERTINTOEmployee(EmployeeName) VALUES(‘Rajendra’);

View the records in the table, and we can see a NULL value against EmployeeID 2 because we did not insert any value for this column.

We might have a requirement to replace NULL values with a particular value while viewing the records. We do not want to update values in the table. We can do this using SQL ISNULL Function. Let’s explore this in the upcoming section.

Лабораторная работа. Изменение формата выводимых чисел

Изменения формата числовых значений в Oracle SQL, функция TO_CHAR для работы с числовыми значениями.

Задание:

Напишите запрос, который бы выводил информацию о имени, фамилии и зарплате сотрудников из таблицы hr.employees в формате, представленном на рис. 3.4-1:

Рис. 3.4-1

При этом данные должны быть отсортированы таким образом, чтобы первыми выводились строки для сотрудников с наибольшей зарплатой.

Примечание:

Некоторые значения зарплаты на рис. 3.4-1 были изменены, поэтому они могут не совпадать с вашими значениями.

Решение:

SELECT first_name AS «Имя», last_name As «Фамилия», TO_CHAR (SALARY, «L999999999.99») As «Оклад» FROM hr.employees ORDER BY SALARY DESC.